Guar Galactomannans Depolymerization Assesment in Yogurt Prepared From Cow Milk

Guar -Galactomannans Depolymerization Assessment in

Yoghurt Prepared from Cow milk

By

Muhammad Umair Ijaz

2006-ag-1808

B.Sc. (Hons.) Agriculture

A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCE (HONOURS)

IN

FOOD TECHNOLOGY

NATIONAL INSTITUTE OF FOOD SCIENCE AND TECHNOLOGY

UNIVERSITY OF AGRICULTURE

FAISALABAD

PAKISTAN

2012

DECLARATION

I hereby declare that the contents of the thesis “Guar -Galactomannans Depolymerization Assessment

in Yoghurt Prepared from Cow milk” are creation of my own research and no part has been copied from

any published source (except the references, standard mathematical or geometrical

models/equations/formulae/protocols etc.). I further declare that this work has not been submitted for

award of any other diploma/degree. The University may take action if information provided us found

inaccurate at any stage. (In case of default the scholar will be proceeded against as per HEC plagiarism

policy).

Muhammad Umair Ijaz

2006-ag-1808

DEDICATIONS

Dedicated To:

MY HOLY PROPHET (PBUH)

My Loving Parents

My Brother

&

My Worthy Supervisor

ACKNOWLEDGMENT

Knowledge is limited and time is short to express the dignity of Almighty ALLAH, the Propitious,

the Benevolent and Sovereignty, the entire source of all the knowledge and wisdom endowed to the

mankind. Lips are trembling and eyes are wet to pray for the Holy Prophet HAZRAT MUHAMMAD

(PBUH); the bacon of enlightment, the fountain of knowledge and the messenger of peace and forever

torch of guidance for humanity.

This thesis arose in part out of a period of research. By that time, I have worked with a number

of people whose contribution in assorted ways to the research and the making of the thesis deserved

special mention. It is a pleasure to convey my gratitude to them all in my humble acknowledgment.

I deem it utmost pleasure to avail the opportunity to express the heartiest gratitude and deep

sense of devotion to my esteemed supervisor, Prof. Dr. Tahir Zahoor for his kind guidance, assistance

and endorsement from the very early stage of this research as well as giving me extraordinary

experiences throughout the research work. This thesis would not have been possible unless his untiring

support and sponsorship. His truly scientist intuition exceptionally inspires and enriches my growth as a

student, a researcher and a scientist want to be. Above all and the most needed, he provided me

unflinching encouragement and support in various ways.

I wish to record my sincere appreciation to the members of my supervisory committee; Dr.

Aysha Sameen and Dr. Sajjad-ur-Rehman for their keen interest, incentive teaching, dynamic

supervision, and valuable comments, scholastic and constructive suggestions throughout my research

work.

Words are lacking to express my obligations to my very special friends and fellows. It gives me

great pleasure to pay thanks to my friends Tayyab Waqas , Sabahat Yaqoob , Nabeel Ahmed and Mian

Imran Sharif who helped me in all possible ways to accomplish this work. I pay ineffable gratitude and

deepest thanks to my all research fellows for their cooperation, well wishes and moral support from

time to time during the course of study.

No acknowledgments could ever adequately express my obligations to my affectionate father,

my dearly loved Mother and all family members who always raise their hands in prayers for me and I

can only say what I am today is just due to their prayers.

Muhammad Umair Ijaz

TABLE OF CONTENTS

Ch. No. TITLE Page No.

1 INTRODUCTION 1

2 REVIEW OF LITERATURE 6

3 MATERIAL AND METHODS 26

4 RESULTS AND DISCUSSION 36

5 SUMMARY 64

LITERATURE CITED 67

LIST OF TABLES

Table # TITLE Page No.

3.1 Treatment Combinations for Product development 32

4.1 Compositional Analysis of Milk 36

4.2 Chemical analysis of Partially Depolymerized Guar Gum 37

4.3a Analysis of variance table for pH of yoghurt 39

4.3b Mean values of effect of PDGG and storage time on pH of yogurt 39

4.4a Analysis of variance table for acidity of yoghurt 41

4.4b Mean Values of Effect of Partially depolymerized guar galactomannans and

storage time on acidity (%) of yogurt

41

4.5a Analysis of variance table for total solids of yogurt 43

4.5b Mean Values of Effect of Partially depolymerized guar galactomannans and

storage time on total solids of yogurt

43

4.6a Analysis of variance table for viscosity of yoghurt 45

4.6b Mean values of effect of partially depolymerized guar galactomannans and

storage period on viscosity (cps) of yoghurt

45

4.7a Analysis of variance table for hardness of yoghurt 48

4.7b Mean values of effect of partially depolymerized guar galactomannans and

storage time on hardness of yoghurt

48

4.8a Analysis of variance table for synersis of yoghurt 50

4.8b Mean values of effect of partially depolymerized guar galactomannans and

storage time on synersis (%) of yogurt

50

4.9a Analysis of Variance Table for water holding capacity of yoghurt 52

4.9b Mean values of effect of partially depolymerized guar galactomannans and

storage time on water holding capacity (%) of yogurt

52

4.10a Analysis of variance table for color of yoghurt 53

4.10b Mean values of effect of partially depolymerized guar galactomannans and

storage time on color of yogurt

53

4.11a Analysis of variance table for appearance of yoghurt 56

4.11b Mean values of effect of guar galactomannans and storage time on

appearance of yogurt

56

4.12a Analysis of variance table for flavor of yoghurt 58

4.12b Mean values of effect of guar galactomannans and storage time on flavor of

yogurt

58

4.13a Analysis of variance table for mouth feel of yoghurt 62

4.13b Mean values of effect of guar galactomannans and storage time on mouth feel

of yogurt

62

4.14a Analysis of variance table for body and texture of yoghurt 64

4.14b Mean values of effect of guar galactomannans and storage time on body and

texture of yoghurt

64

4.15a Analysis of Variance Table for overall acceptability of yoghurt 66

4.15b Mean values of effect of guar galactomannans and storage time on overall

acceptability of yogurt

66

Abstract

Functional Foods are gaining popularity in the world as the consumers are becoming concerned about

impacts of the diets on their health and choose to include foods in their diets, which not only meet their

nutritional requirements but also provide health benefits. Food products containing dietary fiber are

getting a promising trend worldwide because of their role as functional ingredient to enhance the

efficiency of gut microflora and increase the digestibility of food. Stabilizers and thickeners are used in

the commercial and domestic level to improve the shelf life, texture and over all look of the dairy

products. In the present study, yoghurt was developed with starter cultures containing four different

fractions of depolymerized guar galactomannans those are depolymerized at different time intervals

(i.e1, 2, 3, and 4 hours respectively). All the milk samples and depolymerized guar gum samples were

analyzed for their composition (fat, crude fiber, ash and total solids) and physiochemical (pH and acidity)

analysis. Yogurt was processed with the addition of depolymerized guar gum and subjected for its

various physico-chemical and sensory attributes to evaluate the effect of PDGG ON these attributes.Best

results were observed for the T1 and T2 containing PDGG fractions depolymerized for 1 and 2 hours

respectively in same concentration, with respect to the viscosity showing the highest mean as compared

to the lowest mean of control. On the other hand, for firmness highest mean was observed in the PDDG

samples with respect to the lowest for T0 containing no PDGG. The forced syneresis control were

observed most effective for the T2 containing PDGG having lowest means compared to the highest

means of controls, there was a significant effect of the treatments on the spontaneous syneresis of the

yogurt. T0 without PDGG has the highest syneresis while the lowest mean sample was observed for T1

and T2. The same trend was shown the results ofsensory evaluation. Best results with respect to the

textural and sensory evaluation were observed in T1 and T2 Containing Partially depolymerized guar gum

treated for 1 and 2 hours. All the analyses were performed in triplicates and subjected to the statistical

analysis.

CHAPTER-I

INTRODUCTION

Pakistan is primarily an agricultural based country and Livestock plays a pivotal role in

its economy by providing essential items of human diet in the form of milk and meat. The annual

production of milk in Pakistan during 2006 was 38.37 billion liters and putting it 4th in the list of

the largest milk producing countries (Chaudhry, 2007). Milk is a lacteal secretion, practically

free from colostrums, obtained by complete milking of one or more healthy milk animals which

contain not less than 8.25 % of milk solids not fat and not less than 3.25% of milk fat. Milk has a

high energy density per unit of nutrients which provide us opportunity for many kinds of food

products in which milk is an ingredient which not only increases the nutritional value of foods,

but also enhances the availability of minerals. The role of milk products is vital in the human

diet. The nations in which the consumption of the milk is higher are considered healthy.

(Sukumer, 1983).

The growing consumption pattern of fermented milk products is driving force for making

different functional dairy products. Fermented dairy products provide healthy foods for

consumers, having good vitamin and mineral content and small amount of fat. (Hernández and

Harte, 2008). The new varieties of fermented milk products are regularly entering in the

consumer market and Yoghurt is probably the most popular product among all fermented milk

products because of its pleasant flavor and thick creamy consistency (Huma et al., 2003).

The word Yoghurt is associated with the Turkish "Jaukort" which means dense milk.

Different microbial culture pertaining to their respective functions like flavor production and

texture modification are used for the its production along with variety of ingredients such as

fruits, sugar and gelling agents. The culture which are normally used for the production of yogurt

are Lactobacillus Bulgaricus and Sterptococcus thermophillus and almost equal numbers of both

species should be present to develop a satisfactory flavour. (Walstra et al., 1985).The addition of

lactic acid bacteria in dairy products, causes the production of lactic acid from lactose, the milk

sugar, it works on the proteins of milk (Cogan, 2007).

Yoghurt is an important food ingredient in most of societies. It is believed that

consumption of yoghurt and other dairy products is very beneficial for health. The nutrient value

of curd or yoghurt depends on the milk composition and substances added to it during

manufacturing. Yoghurt can be manufactured from skimmed or whole milk and it can be

sweetened, plain or flavoured with fruit juices, cane sugar etc (Srividya and Rao 2003).

In Africa, Asia, Europe and United States yogurt is a dominant fermented milk product

which is marketed under different names around the globe and its processing is carried out

throughout the world. Various types of yoghurts varying in different processing conditions and

added ingredients are available. Some of them are sold like frozen yogurt, simple, stirred type

and set type. The difference lies between the different flow lines of production (Domagala et al.,

2005).

In Indo-Pak Dahi is a similar product to yogurt. Dahi is a domestic milk product usually

developed at home by inoculation of “Jaag” and it is a common name of yoghurt in Pakistan.

Improper storage and incorrect processing conditions are the most important problems by which

traditional yoghurt is being suffered. High syneresis, undesirable texture, variations in taste,

flavor and low sustainability are the major issues during the production of dahi. Traditional

yoghurt is subject to contamination. Large scale production is done in processing plants for

commercial yoghurt with selected bacterial strains (Mahmood et al., 2008).

Yoghurt is a popular milk product with significant health beneficial effects and higher

nutritional value (Wood, 1992). In recent years a lot of interest had been raised by

immunological potentials of Lactobacillus acidophilus due to their properties of immune

stimulating. In vitro, on cells of the immune system stimulatory properties had displayed by

several strains of lactic acid bacteria (LAB), including macrophages. (Weid et al., 2001).

Yoghurt is a food commodity that is more famous as a food standard for the carriage of

beneficial probiotic microorganisms (Adolfsson, et al., 2004). Probiotics are the beneficial

live bacterium leads to benefits the host organism. According to FAO/WHO (2009)“probiotics

are live microorganisms which when administered in adequate amounts confer a health benefit

on the host". The species of lactic Acid Bacteria (LAB) and the species of Bifidobacteria are the

most common categories of microbes that are used as probiotics in most of the foods but some

varieties of yeasts and Bacilli also helpful in maintaining the live of organisms. Yoghurt contains

approximately at least 106 live cells of Lactobacillus and/or Bifidobacterium 10

9. For the

successful addition of probiotics in the foods articles, they must survive the food processing and

storage process practices (e.g., fermented food products). Lactic acid bacteria help in aroma

development, microbiological safety and to improve texture of fermented dairy products

(Grattepanche et al., 2007)

Dietary fiber is “the remnant of the edible part of plants and analogous carbohydrates that

are resistant to digestion and absorption in the human small intestine with complete or partial

fermentation in the human large intestine” (AACC, 2001). Despite of the health benefits of

dietary fiber in the diet, the average consumer consumes less than 50% of the recommended

level of dietary fiber. Therefore, there is a gap between the dietary fiber consumption and

recommendation that needs to be narrowed. Changing consumers‟ eating habit is a difficult and

time taking process but producing popular foods like yogurt fortified with dietary fiber could be

one way to increase dietary fiber consumption without changing their habits (USDA, 2008).

Soluble fiber is becoming more important in the western diet because of a trend toward

consumption of food with lower calories and higher amounts of dietary fiber (Regmi,

Takeshima, & Unnevehr, 2008). Inulin or partially hydrolyzed guar gum and cannot be digested

by human digestive enzymes and hence behave as dietary fibers. They have also been found to

mimic properties of fat in food products (Kip, Meyer, & Jellema, 2006). Addition of these

ingredients to food products like low fat yogurt not only makes them rich in dietary fiber, but

also improves their physicochemical and sensory properties by imparting fat like textures. While

some manufacturers have already produced yogurt with inulin and PHGG, inulin used in most

commercial yogurts is native inulin (with an av erage chain length of 10 units) from chicory root

(Coussement, 1999).

Now days, the importance of dairy products has increased manifold due to the awareness

among the people about the nutritional value of yoghurt. It has been established that fermented

milk products, of which yoghurt is one increase nutritive value of food as compared to original

milk. Different ingredients like cereals, gums, fibers and starches, legumes mixes, fruit pulp and

juices of many medicinal plants added in yoghurt to enhance the therapeutic and quality value of

it (Frank, 2002).

The major problem which reduces the shelf life of yoghurt is synersis; this problem may

be reduced by decreasing the temperature of incubation and acidification rate and increasing the

casein content of the milk (Fiszman et al., 1999), or by addition of stabilizers. The compounds

used as stabilizers in yoghurt are starches, gelatin, alginate, carrageenan, pectin, derivatives of

methylcellulose, tragacanth, gum arabic, locust bean gum (LBG), karaya, guar and xanthan gums

(Tamime and Robinson, 1985). The primary stabilizers such as LBG, alginate, carboxymethyl

cellulose (CMC), or guar gum can be used as a thickener in combination with a secondary

stabilizer such as carrageenan to reduce synersis (Hansen, 1993). Use of soluble fibers as

stabilizer has some advantages (Labell, 1990). By consuming fiber in the diet hypertension,

gastrointestinal disorders, hypercholesterolemia, diabetes and coronary disease may decrease and

put off (Dello Staffolo et al., 2004).

Stabilizers such as starch imparts stability and provides texture to the finished products

through one or more properties like viscosity, elasticity, foaming, emulsification, gelation , and

water binding. These properties make it multifunctional ingredient not only for food products

but also for pharmaceutical and photographic industries. Among the manufacturing of food

products, starch has solid and important role in countless products like jellies, milk and milk

products as yoghurt, puddings, ice cream, sweets like marshmallows and gummy bears, jellied

meat, and aspics (Fernandez et al., 2003).

Different thickeners and stabilizers are widely used in yoghurt including oat, inulin, date

fiber and guar gum to enhance the physic-chemical properties of yogurt. PDGG is also used as a

prebiotics in the products like yoghurt etc. Guar gum is obtained from the beans of guar, where it

acts as a food and has ability to store water. The guar bean is normally grown in countries like

India and Pakistan. Chemically, guar gum is a carbohydrate source made up of the sugars

galactose and mannose. The guar gum is made up of a linear chain of β 1, 4-linked mannose

deposits to which galactose deposits are 1, 6-linked at every mannose, forming short chains side-

branches (Courts, 2010).

Guar gum is soluble non digestible polysaccharides and is main ingredient in the

formation of functional foods having efficiency to reduce the risk of cardiovascular disease and

plasma cholesterol level. The composition of guar gum includes soluble fiber 75%, moisture

contents 9.55%, insoluble fibers 7.6%, crude protein 2.16%, ash 0.54% and fat 0.78%. In guar

gum, total dietary fiber is present in soluble form (80-85%) that may aid to reduce the glucose

and cholesterol levels (Frias and Sgarbieri, 1999).

Guar gum is largely used in Organic yogurt as a stabilizing agent. Carbohydrate based

guar gum is better soluble in cold water and comprised of galactose and mannose units. This is

an edible, viscous fiber and its possible effects on lowering cholesterol and blood sugar. Guar

gum is used in food industry (EU food additive code E412) as a thickener to increase the

viscosity and to bind available free water in ice cream, sauces and dressings, meat and sausage,

pet foods, instant noodles, bread improvers and beverages (Butt et al., 2007).

Guar gum can be used in a partially depolymerized (PDGG) form and then added in the

yoghurt as a dietary fiber and prebiotic. The guar gum which is depolymerized partially is a

water soluble dietetic fiber that acts as a prebiotic and enhances the efficiency of probiotics in the

gastrointestinal tract (GIT). Even though guar gum has optimistic physiologic health benefits, its

high viscosity marks it problematic to add into food products and eternal solutions (Ellis et al.,

2001). PDGG provides a dietary fiber source that could be easily added to the food products and

would be acceptable to consumers. PDGG is developed by controlled partial enzymatic

hydrolysis of guar gum. PDGG has a very low molecular weight and low viscosity than original

guar gum powder. PDGG is very stable, higher water retention capability and imparts only a

mild flavor to the product (Greenberg and Sellman, 1998).

Keeping in view the significance of guar galactomannans the current study was designed

with the following objectives

OBJECTIVES:

• To characterize depolymerized Guar-Galactomannans.

• To elucidate the effects of Guar-Galactomannans on physic-chemical and sensory

features of yogurt

CHAPTER-2

REVIEW OF LITERATURE

The civilization of the Middle East used fermentation for the preservation of milk. The

term yogurt came from Turkey for fermented milk products. The yogurt has been playing its role

for health benefits in the diet and life of peoples since old days. Today customers are more aware

about dietary attributes of the foods they are consuming. Fermented dairy products, including

different yogurts whether they are low fat or full fat, increase the overall nutritional value of that

product produced from the milk. To improve the quality and health benefits of the yogurts,

different fat substitute from many sources like inulin, carrageenan, pectin, guar gum and starches

are used in various formulations.

By reviewing the previous works, new researchers make different strategies to carry out

research work. Review of literature illuminates the conclusions of the previous studies and

abolishes any chances of unwanted repetition in the design of new work.

To support the study, literature has been cited under the following headings:

2.1. Yogurt and its processing techniques

2.2. Types of yogurt

2.3. Nutritional and Therapeutic Properties

2.4. Rheological Properties of Yogurt

2.5. Physico-chemical and Sensory Analysis of Yogurt

2.6. Effect of Stabilizers on Quality of yogurt

2.7. Partially Depolymerized Guar Galactomannans as a Stabilizer

2.8. Guar Galactomannans and Health benefits

2.9. Yogurt Storage

2.10 Effect of storage on Rheological Properties

2.1. Yogurt and its processing techniques

According to FAO/WHO standards, yogurt is „the viscous milk product achieved by the

fermentation of milk by the action of lactic acid bacteria i.e, Lactobacillus delbrueckii ssp.

bulgaricus and Streptococcus thermophilus (Krasaekoopt et al., 2005).

2.1.1. Methods of production

2.1.1.1. Traditional Methods

There is a great certainty that Middle East was the origin of yogurt, in old days the

fermentation process of milk was uncontrolled and unpredictable but with the passage of time

variations in the practices of different people brought tremendous changes in the production

methodologies of fermented products. Goats, sheep, camels and buffaloes are the domestic

animals that are farmed in most part of the world for milk. Progressively, people adopted a

fermentation process for souring the milk in a controlled way (Tamime and Robinson, 2007).

Domestically yogurt is produced in a process that includes following steps:

• Heating the milk in a vessel on flame to thicken the milk. It attains a specific viscosity and

desired properties by the action of modified casein, a change in protein profile which has the

potential to improve the quality of the final product.

• Inoculate the heat treated and cooled milk with sour milk (as a starter) from previous batch, or

with starter culture (bacteria).

• Incubation (stay time) for 8-10 hours.

• For regular continuation of the process, apply the same vessels in which fermentation was

done, based mainly on the natural micro flora of sour milk or add fresh milk in that vessel.

(Tamime and Robinson, 2007)

2.1.1.2. Industrialized/Commercial methods

Methods for the yogurt development in milk processing industries have been changed

over the years particularly, the selection techniques for the lactic acid bacteria that bring about

fermentation in milk. The whole industrial fermentation process require some refinements and

rest of the process is as follow.

• Increasing total solids content of the processed milk up to the level of 14 - 16 g / 100 g.

• For milk, high temperature for 5-30 minutes is an ideal heating method. The exact time

depends on the selected temperature.

• Inoculation of the milk with a specific bacterial culture in which Lactobacillus bulgaricus and

Streptococcus thermophilus are the dominant organisms.

• Cooling and, if desired, additional processing, such as fruit and other ingredients, pasteurization

or the concentration of the mixture.

• Packaging in cold containers for distribution and end consumers.

(Tamime and Robinson, 2007)

2.2. Types of Yogurt

Different mammalian species have been used for milking and yogurt production.

Variations in yogurt quality depend on the type and quality of milk. For yogurt starter culture

milk lactose is the source of energy and food. Protein in yogurt forms the coagulum and

maintains the consistency. Viscosity of the yogurt directly depends on the levels of protein.

Flavor of the yogurt owes to the biochemical reactions commenced by the microbial activity.

The flavor of the yogurt varies from species to species.

Commercially available yogurts can be categorized on the basis of their chemical nature,

processing technique, flavor and the different types of processes after incubation (Shah, 2003).

Based on different fat percentage these are classified as:

(1) Full-fat yogurt

(2) Low-fat yogurt

(3) Non-fat yogurt

On the basis of the production methods, yogurt can be classified as set-type and stirred

type yogurt. If milk is fermented to form yogurt in a retail vessel, it is known as set type yogurt.

In stirred type yogurt, different containers are used for fermentation and viscous gel matrix is

broken down by stirring before cooling and packaging. Similarly, flavored yogurt can be divided

into subgroups. Fruit yogurts have fruit particles which are added for improvement in taste,

sweetness and color (Shah, 2003). Apart from typical plain yogurts, fruit yogurts are capturing

huge market volume.

Currently, there is huge variety of yogurts available around the globe depending upon the

market demand. Tamime and Deeth (1985) presented their yogurt classification scheme which

has four physical characteristics to distinguish the product. Different grouping based on

following guidelines covers the product range of yogurts in markets.

• Legal standards of the product i.e., chemical or fat content covering semi skimmed/low fat to

middle or so.

• Physical features of the product i.e., nature, set type, or stirred or drink fluids. Others are low

viscosity stirred yogurt.

• Flavoring nature either plain/natural, fruit flavors or artificial. The latter two types are usually

sweet.

• Supplementation and fortification standards (Tamime and Robinson, 2007).

2.3. Nutritional and Therapeutic Properties of Yogurt

With respect to nutritional essay, both milk and yogurt have many similarities except in

those stirred type yogurts in which the yogurt is fortified with fruits, grains or other components.

The nutrition equality of both milk and yogurt means that yogurt has protein, thiamin, riboflavin,

calcium, phosphorus and vitamin B12 and an excellent source of folate, niacin, magnesium and

zinc. Its mineral bioavailability is of great importance having good biological value. Also, low-

fat yogurts provide energy with low fat content and making it dense nutritional foods creating a

significant amount of important nutritional matrix (McKinley, 2005).

The major minerals which are inevitable for growth and development of human body are

calcium and phosphorous. Yogurt can fulfill 40% calcium and 35% of phosphorous requirements

of the body. Calcium brings improvement in the immunity of the body, lowers the blood

cholesterol levels and helps in bone formation and deposition of calcium in bones. Moreover,

yogurt helps in the magnesium absorption due to the presence of lactic acid bacteria that make

possible the efficient mineral absorption (Adolfsson et al., 2004).

Various studies have confirmed that per unit value of solids-not-fat (SNF) or dry matter

without fat weight is higher in yogurt than milk, which clearly indicates the presence of

substantial amount of inorganic ions. For lactose intolerance people, yogurt is the best available

source of calcium in diet as it is readily available. Yogurt has good digestibility and no

symptoms of lactose intolerance were observed after consuming yogurt by the persons suffering

from this disorder. Calcium has very crucial role to play in bone metabolism and curing action

against osteoporosis. The availability of calcium in yogurt is the best than any other dairy

products (Rasic and Kurmann, 1987).

Like yogurt, cultured milk products are in used since ancient times for so many reasons.

Most importantly, the proven health benefits related to LAB bacteria in the yogurt that inhibits

the growth of other harmful microorganisms. Over the years, the food industry is working on

carbohydrate based prebiotics which account for major development in selected strains of

probiotic bacteria. These probiotic bacteria and microorganisms are being used for significant

improvement in health (Shah, 2007).

Different fruit and fruit preparations are added in yogurts for giving it more healthy

image along with its antioxidant potential (O‟Rell and Chandan, 2006). Recently, soymilk yogurt

(Donkor et al., 2007c; Champagne et al., 2009), yogurt from corn milk and peanut milk yogurt

(Isanga and Zhang, 2009) have been developed as an alternatives for vegetarian consumers that

avoid to have bovine milk yogurt. This approach can also reduce the allergic reactions associated

with milk proteins and lactose intolerance. Use of tea catechins in dairy products as an

antioxidant and antimicrobial properties of plant origins have been studied by using plant extract

in yogurt (Jaziri et al., 2009). The low-fat yogurts offer range of vital nutrients in substantial

amounts with respect to their energy and fat content, consequently rendering them a nutritious

and wholesome food (Shah, 2003; McKinley, 2005)

2.4. Rheological Properties of Yogurt

Ozer et al. (1998) conducted a study on microstructure and rheology of Labneh

(Concentrated Yogurt). They prepared labneh by increasing solid contents of milk to almost 23%

(wt/vol) by the traditional cloth bag method (control), reverse osmosis, ultrafiltration and direct

reconstitution. Their studies revealed that physical behavior of labneh are affected by rheological

properties which was highly reliant on concentration of protein and during membrane treatment

the rigorousness of mechanical agitation. It is shown by Scanning electron microscopy that

samples with higher protein content had firmer structure and small cells as compare to samples

with lower protein contents.

Skriver et al. (1999) investigated relation between rheological properties and sensory

texture analysis of stirred yogurt. It was found that the rheological and sensory characteristics of

stir style yogurts varied with dry matter content, heat treatment of milk, composition of bacterial

cultures and fermentation temperature. Two self-determining sensory properties, oral viscosity

and non-oral viscosity were also assessed. Oral and non-oral viscosities were modeled

successfully by partial least squares regression, from rheological variables that result in a model

with three component that explained 83.8% of the non-oral viscosity variation and a model with

two component explaining 82.0% of the oral viscosity variation. The viscosity was measured

from a Brookfield viscometer operated at 5 rev/min (r = 0.862).

Jumah et al. (2001) examined influence of milk source on rheological attributes of

yoghurt in course of the gelation process. It was elaborated by them that highest viscosity value

was shown by the ovine milk then comes caprine, bovine and camel milks. No major variation in

viscosity was observed in camel milk during gelation. Mainly the rheological properties of

yogurt are affected by the chemical composition of milk specially protein content and total

solids.

Lee and Lucey (2004) observed an increase in hydrophobic interactions with the rise in

incubation temperature which results in shrinkage of casein particles and a more compact

conformation during the study of physical properties and structure of yogurt gel: effect of

incubation temperature and inoculation rate. It is revealed by this study that incubation

temperature and inoculation rate are important processing factors that influence physical and

microstructural traits of yogurt gels.

Becker and Puhan (1989) describe that firmness significantly increases with high protein

content. Skimmed yogurt has higher firmness values than whole yogurts under all storage

conditions.

Pandya et al. (2004) reported that with increasing fat content sensory properties and

rheology of buffalo yogurt significantly improved (P<0.05). by increasing the fat content from

1.5 to 4.5%, viscosity was increased by22.5%, curd tension improved by 10% and wheying off

decreased by 31%

Amatayakul et al. (2006) investigated the effect of levels of solids and

exopolysaccharide. starter culture on the syneresis in set style yogurt and determined the by

centrifugation method, siphon and drainage influenced by(EPS). The product which was made

by using EPS as a starter culture showed whey separation at a higher level as compared to non-

EPS as a starter culture and the whey separation was 9%, determined by centrifugation.

Lee and Lucey et al. (2003) investigated the rheological properties e.g. heating and

incubation temperature and microstructure in set- style yogurt storage and it was reported that

storage module was increased in heating temperature as compared to incubation temperature.

With the rise of heating temperature give good results and diminution in temperature for

incubation otherwise spontaneous whey separation and maximum permeability will occur.

Ares et al. (2006) measured the firmness in stirred yogurt results showed that yield stress

was with-in range of 250 Pa from manufacturing plants. During fermentation when final acidity

was varied then it gives the more pronounced results and it shows the value of a standardized

production for obtaining uniform texture. The yogurts made from processing unit showed

expressively more yield stress as compared with samples from the different retail stores. During

handling and distribution, syneresis was also occurred due to mechanical damage.

2.5. Physico-Chemical and Sensory Analysis of Yogurt

Yogurt is a kind of gel, soft solids so it is sensitive to structural changes. Various

procedures are outlined to investigate structural and physical features of yoghurt. Different

processing of the variables was influence the structural properties of the yogurt, such as the total

content of solids, incubation temperatures and heat treatment. By better understanding of those

factors that lead to structural and physical properties, could improve the yogurt quality. (Lee and

Lucey, 2010).

Yogurt is made from different heat treated milk samples and viscosity was measured

through viscometer (Brookfield DV-E Model) with spindle No. 3 at speed of 20 rpm. Average

viscosity of all types of yoghurt was decreased by increasing in the heat treatment to milk

samples. The entire yogurt from milk samples formed at 90°C/10 min is less noticeable to

decline in viscosity occurring throughout storage (Djurdjević et al., 2002).

Skimmed probiotic yogurt was stored at 7°C. A group of qualified judges analyzed the

cooled dahi‟s quality. pH decreased apparently, with storage time, showing that much acidity

was not developed by dahi samples under the storage environment. After giving 8 days for

storage, jury concluded that slight bitterness in samples is common. Based on the consequences

of this study, it was concluded that dahi was accepted by consumer up to 8 days during storage.

(Yadav et al., 2007)

Texture analysis of yogurt was performed by texture analyzer. It had been found that the

use of various quantities and types of polysaccharides used in the formulation did not affect the

pH, salt, ash, protein, water, fat and cholesterol, and acid strength values of samples (Seckin et

al., 2009).

As a result, consumers access to samples of yogurt in a structured hedonic scale of 9

points. Consumers were able to express a preference decisions, because the research was

conducted with the researcher. Possibility was there to determine the part of customers that gave

similar hedonic response for yogurt but still had some preferences for one or the other of the

stimuli (Villegas-Ruiz et al., 2008).

Tarakci and Kucukoner (2003) studied different properties like sensory, physico-

chemical and microbiological properties of fruit-flavored yogurt and reported that there were

significantly differences in the fat, ash, protein, total solids (TS) content and titratable acidity

(TA) for samples amounts 1day of storage. There were marked differences in the protein and

dry matter due to different flavor additives. Syneresis and titratable acidity (TA) increased over

the storage period.

Ahmed (1999) prepared the fortified yogurt by incorporating the sugar and mango fruit

pieces noted its shelf life when kept at 6 degree centigrade for 40 days. He observed that there

was a slight decrease in the acidity of the yogurt samples. The addition of sugar caused syneresis

whereas substantial increase in total solids. The incorporation of mango fruit pieces in the yogurt

also increased the rate of syneresis. It was observed during storage of the yogurt samples at 6

degree centigrade that there was substantial increase in the amount of acidity, total solids and the

rate of syneresis. The pH of yogurt samples decreased significantly.

Hardi and Slacanac (2000) investigated that rheological properties are important factors

in the quality of yogurt. Texture depends upon a number of factors including starter culture, milk

composition, milk viscosity, heat treatments, fermentation kinetics and homogenization. The

effects of three factors (milk fat content, starter culture and addition of inulin) on coagulation and

rheological properties were examined in yogurt, the result showed that starter culture had

greatest effect; inulin addition caused an increase in consistency of probiotic product compared

with yogurt.

Harper et al. (1991) investigated the sensory ratings in marketable plain yogurts by

consumer and descriptive panels and it was found that samples rated highest in overall liking

had sourness ratings closest to just right on the “just right” scale. Ratings for all descriptors by

the descriptive panel were significantly different. Sourness, with high intensity ratings, was most

important in describing plain yogurt. Samples rated most favorably by consumers had lower

intensity ratings for overall intensity, sourness, acetaldehyde, saltiness, and astringency and

higher intensity ratings for sweetness, milkiness, and cooked milk. Titratable acidity and pH

were correlated with many trained panel descriptors important to consumer acceptability. Better

control of pH by yogurt processors would result in more favorable sourness levels, which should

increase consumer acceptability.

Chee et al. (2005) studied sensory and chemical properties in strawberry flavored yogurt

emulsified with algae oil, by hydro-peroxide measurements the oxidative deterioration was

reported after sensory evaluation by skilled panel consumer. In this supplemented yogurts the

hydro-peroxide content was increase over the storage treatment and was unchanged by the stage

of addition. After completion of 22 days storage sensory evaluation was done by trained and

qualified panel and they could distinguish a stronger fishy flavor and consumer voted as

„moderately liked‟ for both.

Damin and Oliveira (2003) studied sucrose and total solid content on firmness, acidity,

feasibility and viability of pro biotic bacteria in fermented milk and reported that milk samples

containing higher levels of total solids showed higher acidity and increasing the amounts of

sucrose and total solids in milk resulted in higher firmness. Anema et al. (2004) examined

viscosity of heated reconstituted skim milk as influence by pH when it was being set between 6.5

to 6.7 and temperature for heating at 90ºC for 30 min. He reported that variation in viscosity was

dependent on pH of the milk and heating. At initial steps of heating, viscosity increased

remarkably at pH 6.5 and platitude on extended heating. But as pH value of milk amplified,

minute variations in viscosity examined at 6.7 pH value. There was a linear correlation between

change in viscosity and change in particle volume.

2.6. Effect of Stabilizers on Yogurt Quality

Stabilizers have been used for several purposes in food products. These may impart

stability, thickening and better mouth feel to the food products. Stabilizers are categorized with

respect to the manufacturing process.

According to Glicksman, (1982) stabilizers may be of natural, customized or synthetic

origin. There were many variables that effect the selection of stabilizer or stabilizer combination

to be employed. A few concerns about the selection of a stabilizer were considered, like legal

aspects, their reactions with other ingredients, their functional properties, their intended use and

outcome. In yoghurt the stabilizers are added due to the following two reasons. As gelling and

thickening agents and to stabilize the gel matrix. Stabilizers played an important role in yoghurt

manufacturing. In this way the hydrocolloids which were added in the milk before the

fermentation process can develop the viscosity, sustain the yoghurt structure, change the mouth

feel, decrease synersis and help in keeping fruit in suspension in the yoghurts.

Kalab et al. (1975) examined the effect of thickeners on the microstructure of yoghurt by

using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). They

demonstrated that there was a formation of long, thin fibers joined with large bunches of casein

micelles in yoghurt by the addition of carrageenan at 0.4% concentration, giving rise to a fibrillar

microstructure of yoghurt. They also showed that no change was occur in structure of yoghurt by

the addition of gelatin studied by transmission electron microscopy (TEM) and scanning electron

microscopy (SEM). The yoghurts contained gelatin i.e. 2% and 10% when studied by TEM,

showed no microscopic difference in the gels.

McGregor et al. (1987) discussed the effect of two sweeteners on the flavour of plain and

stirred yoghurt. Blue berry or strawberry fruit flavouring added plain and stirred yoghurt were

examined before and during storage at 40C or 10

0C for 24 days. They concluded that there was

no significant difference between sweeteners in the time required for yoghurt to reach pH 4.4.

Yoghurt had the highest Lactobacillus bulgaricus count made with 90% fructose and sucrose

syrup whereas sucrose increased viscosity significantly. On storage at 40C than 10

0C flavour and

sweetness scores were better and acetaldehyde and acetone contents were higher.

Teggatz and Morris (1990) described that the use of thickeners, which increase firmness

and prevent synersis was an additional way of improving the consistency of some milk products,

besides the addition of milk solids. On the other hand some people think that taste, aroma and

mouth feel of true yoghurt are badly affected by addition these additives.

Ramaswamy and Basak (1992) demonstrated that stability of the product may be reduced

by the addition of flavourings or fruit concentrates, which therefore commonly requires some

stabilizers like starch or pectin with products. For fermented milk beverages, optimum stability,

no serum separation and uniform consistency for good mouth feel are most wanted

characteristics.

Hansen (1993) described that locust bean gum, guar gum, carboxymethyl cellulose

(CMC) or alginate are the primary stabilizers may use as a thickener in combination with a

secondary stabilizer like carrageenan to reduce syneresis. Casein network was made stronger by

interaction between the positive charges on the surface of casein micelles and the anionic

hydrocolloids (e.g. CMC, pectin, and carrageenan) while synersis was reduced and categorized

as adsorbing polysaccharides. Xanthan, guar and locust bean gum are neutral hydrocolloids do so

through a another mechanism by increasing the thickness of the continuous phase and are

categorized as non-adsorbing polysaccharides.

Jawalekar et al. (1993) examined the use of gelatin and many other stabilizers associated

to yoghurt sensory quality and rheology, in addition to whey separation. It was examined that

due to the use of gelatin there was development in texture, body, viscosity and curd tension in

yoghurt whether that was prepared from buffalo or cow milk. As the free water was bound with

stabilizer, there was less synersis in the yoghurt. Besides to gelatin, pectin and CMC, several

other stabilizers like starches, locust bean gum, agar, guar gum and algenates have been analyzed

for their use in yoghurt. The characteristics, functionality and amount of these ingredients may

all influence the mouth feel and approval of a yoghurt product.

Guinee et al. (1995) examined that the firm gel was formed on the peanut milk based

yoghurt with no whey at the top even when no stabilizer is added to it but addition of stabilizer

like gelatin improved its sensory attributes. It means that stabilizer in yoghurt based peanut milk

was mostly helped in improvement of sensory attributes but not for reaction of whey separation

or firmness of gel. A firm gel without whey at the summit was formed by the gelatin and had the

higher sensory scores for all the features (texture, acceptability and appearance) as evaluated to

other stabilizers (PGA, CMC, HM pectin, xanthan gum, guar gum and κ carrageenan).

Shukla et al. (1998) studied the effects of gelatin, pectin, CMC and some other stabilizers

on the rheological and amount of whey separation properties of yoghurt, made from the buffalo

milk. It was found that gelatin with the percentages of 0.1% to 0.3% improves the appearance,

texture, body and flavor of the yoghurt. In the manner, pectin with percentages of 0.2 to 0.3%

was found positively correlated with the quality attributes and negatively correlated with whey

separation. On the other hand CMC affected yoghurt qualities negatively and the samples in

which it was used were found unacceptable for sensory analysis. And it was recommended that

the amount of CMC should not be used more than 0.1%.

Celik and Bakirci (2003) investigated some features of yogurt manufactured by

incorporating concentrated juice and check the properties like pH, titratable acidity, whey

separation and viscosity for 28 days with the intervals of a week. As compared to control during

its storage, the viscosity, whey separations and titratable acidity was higher than those of

controls.

Farooq and Haque (1992) studied the rheological traits of low fat yogurt. For sweetness

of yogurt aspartame was used (200 ppm) to a skim milk based yogurt and to stabilize it 5%

starch was added. The total solids content was 12.68% by weight. The overall quality of the

yogurt was improved by adding esters of sugar in the form of Aspartame. Yogurts had better

body, texture, and mouth-feel with sugar esters, mainly the stearates as compared with yogurts

without sugar esters, which were rated as grainy, coarse and rough mouth-feel. So, perception

rate was increased by adding sugar.

Salwa et al. (2004) studied the yoghurt‟s sensory, chemical, microbiological properties

after adding carrot juice and rate of consumer acceptance to consume this yogurt and reported

that the sensory scores increased particularly for yoghurt samples in which 15% carrot juice was

used. Chemical analysis showed that if quantity of carrot juice is increased then acidity was

increased, soluble nitrogen or total nitrogen ratio was decrease and also the tension of curd. If it‟s

shelf life is concerned then carrot juice showed significant results. The other discussion was on

consumer perception as well as on economy of adding carrot juice.

Tayar et al. (1995) observed influence of addition of stabilizers on yogurt‟s quality. They

discussed the properties like serum separation, titratable acidity, water activity (aw), and

organoleptic value of the yogurt by adding gelatin, agar or sodium caseinate at levels of 1, 1.5,

2.0% over 14 days storage at 4±1ºC. All stabilizers decreased the serum separation and increased

the quality.

Tamime and Robinson (1999) studied the effect of stabilizers on yoghurt quality. They

concluded that under different conditions and their interaction with milk casein, the negative

effects of some stabilizers were showed on yoghurt quality. The production of different types of

yoghurt was depended on the action of selected stabilizers but in most application trial and error

method was the thumb rule.

Fiszman et al. (1999) made a study of the effect of gelatin addition on acidic milk gels

microstructure and yoghurt on their rheological properties. The objective of this study was to

observe the effect of the gelatin addition on the yoghurt and microstructure of acid-heat-induced

milk gels while yoghurt made with or without addition of milk solids at concentrations of 5%.

The results of this study exposed significant microstructural differences among yoghurt

formulated with and without addition of gelatin at two levels of total milk solids. The results

explained that the yoghurts made without addition of gelatin showed less solid-like behaviour

than the yoghurts prepared with addition it. According to firmness tests it was seen that in all

cases the gelatin addition at the concentration of 1.5% developed deformable and fairly firm

systems. It was also seen that the gelatin interacted with milk proteins network in yoghurt and in

the acid-heat-induced gels. At the end results obtained that quality of milk products can be

improved by the use of gelatin.

According to Drake et al. (2000) selection of stabilizer used may also a contributing

factor of chalkiness in the yoghurt products. Choice of stabilizer used has been categorized as the

crucial ingredient by The National Starch and Chemical Company. As the choice of a particular

stabilizer may reduce or impart chalkiness, depending upon its properties. There were also many

conditions which affect the mouth feel. High temperatures during processing, unstable casein and

a rapid development of acid have all been found in yoghurt as means for a grainy mouth feel,

which had similarity with the chalkiness

Schmidt et al. (2000) used stabilizers i.e. modified wheat starches in set-style yoghurt.

They formed yoghurt with the addition of modified wheat starches (MWS) (hydroxypropylated

cross-linked, hydroxypropylated or acetylated cross-linked), gelatin and native wheat starch

(NWS). During 2 months of storage, chemical (titratable acidity, fat, pH and total solids),

physical (rheological, textural, color, synersis) and microbiological (yeasts/molds and lactic acid

bacteria) characteristics of yoghurt samples were evaluated. It was significantly showed that the

greater storage modulus and firmness of the yoghurt formed with NWS as compared to yoghurt

prepared with MWS. In all yoghurt samples minimum synersis was measured. They observed

that during storage pH of yoghurt samples decreased and the titratable acidity increased. By the

day 60 in all yoghurt samples ~ 1 log CFU/g lactic acid counts were decreased while

yeasts/molds did not detect. They concluded that positive effects were produced to varying

degrees by the use of wheat starches as stabilizers in the yoghurts. Yoghurt made with NWS and

gelatin having alike characteristics, therefore NWS might be used as a substitute of stabilizer.

El-Sayed et al. (2002) investigated the effect of xanthan gum which is produced in

laboratory and its combinations at different concentrations with other gums on the sensory,

rheological, micro-structural chemical and microbiological properties of yoghurt and soy

yoghurt. Fresh or during storage of yoghurt and soy yoghurt samples pH-values, changes of

lactic acid bacterial counts or contents of total solids were not affected by the addition of xanthan

gum or its mixtures. Additionally, they did not detect yeasts and mould as well as colliform

groups with any treatments, either in fresh or storage period. The type and concentration of

stabilizer used affected the values of viscosity of both type yoghurts. The curd tension of milk

yoghurt was increased by the use of xanthan gum or its combinations at tested concentrations. At

the concentration of 0.01% of xanthan gum in yoghurt samples showed higher the curd tension

values whereas there were variable effects seen on curd tension when the addition of xanthan

gum or its combinations in soy milk yoghurt. Addition of xanthan gum or its mixtures in yoghurt

decreased the synersis of it although no synersis was noticed in any fresh soy yoghurt samples.

Highest sensory scores were obtained as compared with other treatments when xanthan gum at

the concentration of 0.01 and 0.005% was used in yoghurt and soy yoghurt respectively.

Koksoy and Kilic (2004) examined that the different concentrations of guar gum, locust

bean gum and high methoxy pectin in conventionally prepared Ayran to prevent separation of

serum. The highest apparent consistency and viscosity index were provided by guar gum and

prevented the separation of serum in Ayran. But the mouth feels that was not acceptable for

Ayran. At 0.50% concentration of high methoxyl pectin prevented separation of serum in Ayran

which affected the odor and the taste of Aryan. At 0.10% level of locust bean gum prevented

separation of serum and apparent viscosity was increased without affecting the odor and the taste

in Ayran.

David et al. (2005) suggested by the study that the mechanism of casein aggregate

stabilization remained consistent when the level of l-carrageenan and anionic low methoxy

pectin was increased. On the aggregate surface an adsorbed satiric repulsion layer was also seen.

The charge attraction of electrostatic lowered the aggregates and increased the propensity

towards reduction flocculation by the unabsorbed fraction of the stabilizer. The rheological data

by low methoxy pectin at low concentrations is constant with bridging flocculation of

aggregates. Increasing level of anionic stabilizer resulted in higher water holding capacity as the

ability of the amount of casein aggregation to trap serum phase was less within the protein

matrix. It was indicated that a satiric stabilization method played an important role to counteract

the aggregation process.

According to Avena et al. (2006) as gelatin was found deficient in tryptophan and

methionine so it is not considered as the proper source of protein, yet by containing 4% lysine

the digestibility is superb and it had been utilized frequently in feeding invalids. Its consumption

of 7 to 10 grams per day indicated that it improved nail strength and growth significantly

according to a controversial study. Gelatin had also been found beneficial in diseases like

arthritis and related diseases in many cases.

Singh and Byars (2007) replaced milk solids with starch-lipid composites (SLC) in

yoghurt mixes. The studied the effects of the SLC on the yoghurt rheology and fermentations.

During the fermentation of yoghurt they evaluated the fermentation rate by the change in pH.

During three weeks of storage they observed the synersis of yoghurt. By using a vane geometry

method the loss tangent, small amplitude oscillatory shear flow and the loss modulus

measurements of the storage modulus were obtained. They concluded that higher the level of

SLC of yoghurt mixes when initial viscosity was higher. Gel structure was not affected by the

higher initial viscosity. SLC addition above 3% level strengthened the gel. The result of this

study that there was no synersis for yoghurt samples during storage at 40C for 21 days.

Nalinanon et al. (2008) described that use of gelatin in yoghurt as a stabilizing agent. It

had been used with percentages ranging from 0.3% to 0.5% to control the synersis in stirred

fruited yoghurt or in general yoghurt recipes. Gelatin in this way reacts with milk casein to

minimize its affinity to separate from water and provide stability to curd.

Fatemeh and Soleiman (2009) observed the effect of gum tragacanth on prevention of

serum separation. They also studied the influence of insoluble and soluble fractions of gum

tragacanth (GT) on it. They used zeta potential, microscopic and rheological measurements for

the investigation of stabilization mechanisms. According to their findings, the concentration of

0.100 % of the soluble tragacanthin (T) and 0.200 % of gum tragacanth (GT) prevented serum

separation. Moreover, Newtonian was the suitable rheological model for control while Power

law was for the others. Dough‟s containing GT and T showed prominent elastic and viscose

behaviours respectively on the basis of viscoelastic experiments. In addition, the zeta potential

values were changed from positive to negative in the presence of T and GT. It was made cleared

that tragacanth adsorbs onto casein and induces stabilization via satiric and electrostatic

repulsions. Furthermore, by increasing the viscosity the insoluble bassorin (B) may assist

stabilized.

2.7. Partially Depolymerized Guar Galactomannans as a Stabilizer

The study examined the effect of gum arabic and guar gum on the physico-chemical

behavior and sensory traits. Viscosity is greatly affected by the gums treatment. Highest

viscosity of yogurt was obtained by incorporation guar gum at 0.3% level. Guar gum and gum

arabic at level of 0.2% and 0.5% respectively showed the better acceptance (Rezaei et al., 2011).

Guar gum and locust bean gums are extensively used in the food industries as thickening

and stabilizing agents, usually in amounts of <1% of the foodweight. For example, they have

been used to improve shelf-life and prevent creaming or settling in salad dressings, soft drinks,

and fruit juices. Locustbean gum is also used to improve freeze-thaw behavior of frozen products

including ice cream and frozen desserts. Guar gum, used in baked productsand pastry, reduces

degree of starch retrogradation and improves texture and shelf-life. Low grades guar and locust

bean gums and their derivatives also found applications in other industries including mining,

paper, textile, andoil drilling (Phillips and Williams, 2000).

The effect of the addition of guar gum at level of (0, 0.1%, 0.2% and 0.3%) was analysed

for sensory and textural attributes of yoghurt. The increase of guar gum concentration increases

the viscosity of the mixture acids. Guar gum increases the hardness of the product. Yogurt

produced in control condition showed less sticky and rubbery appearance. (Milani and Koocheki,

2011).

Syneresis and quality of yogurt was affected with the addition of various stabilizers.

Yogurt was prepared using seven different stabilizers. Guar gum was used at concentration of

0.4%. pH, syneresis level and acidity was assessed during different storage intervals. Significant

decline in value of pH and rise in value of acidity was experienced in all the samples during 15

days at 10°C. Due to production of lactic acid, lactose contents in all yogurt samples were

decreased during storage. (Athar et al, 2000).

Yogurt prepared with various stabilizers such as guar gum at various levels (0.1, 0.2, 0.3,

0.4 and 0.5%) and examined the quality parameters for 21 days during storage. 0.1%

concentration of guar gum approved to give excellent results for production of low acidity and

low pH, where as the cornstorch had better results for the free fatty acids, acetaldehyde contents.

(Mehmood et al., 2008).

2.8. Guar Galactomannans and Health benefits

Guar gum is a gel producing galactomannans acquired from the endosperm part of

leguminous plant Cyamoposis tetragonolobus L. grown in the countries of Pakistan and India. It

is used by the human beings and as well as for the animal food. (Goldstein et al., 1973)

In 1949, guar gum was used in the food products in USA for the first time. Guar gum is

produced from the seeds of the guar plant by grinding the endosperm portion and largely used in

the food industry as emulsifying and thickening agent to stabilize the food products. Guar gum is

mainly comprised of galactose and mannose units linked together through β-D-(1-4)-glycosidic

linkage and they are present in ratio of 1:2 respectively (Stephen, 1983).

Many natural sources are being utilized as galactomannan such as soy beans, pine apple,

coffee, locust beans and sugar beets and having potential benefits when included in the diet of

human beings and also on the rheological and textural properties of food products (Yoon et al.,

2007)

In a study by Giaccari et al., 2001, 134 patients with IBS were divided on the basis of

body-mass index into obese and normal categories, and were given 5 grams per day of PHGG in

their diet for 24 weeks. Both obese and normal patients showed an increase in the frequency of

bowel movements and decreases in the frequency of such IBS symptoms as flatulence,

abdominal tension, and abdominal spasm. While no change in plasma electrolytes was observed,

there was a higher incidence of normal levels of blood cholesterol, lipids, triacylglycerides, and

glucose than prior to treatment.

The partially depolymerized guar gum has been shown to flatten the blood glucose

tolerance tests. They also decrease the rate of gastric emptying. It binds with bile acids that

surround fat molecules in order to carry them out of the body. This results in decreased

absorption of cholesterol and lipids as well as an increase in fat excretion (Asp. and Johansson,

1984)

Yamatoya et al., 1993 has declared the effects of Partially hydrolyzed guar gum(PHGG)

on postprandial plasma glucose and lipid levels in human. Moreover, as PHGG passes through

the stomach, it slows the rate of emptying, therefore providing a feeling of fullness.

Guar gum has been shown to lower blood cholesterol levels in numerous animal and

human studies. Hypothetical mechanisms of actions include impaired absorption of dietary

cholesterol or bile acids due to the viscous nature of the polysaccharide and impaired absorption

of bile acids through direct binding to the fiber. On the other hand, viscosity is not the whole

answer to the question of plausible mechanisms of action in reducing blood cholesterol. It has

also been suggested that gums such as guar gum are readily available for colonic fermentation,

with the production of short-chain fatty acids, particularly propionate, which has been shown in

animal and human studies to lower blood cholesterol through a suppression of hepatic

cholesterol synthesis. (Evans et al, 1992)

In another randomized double-blind crossover study of 20 individuals with moderately

elevated plasma cholesterol performed by 36 participants received either control wheat bread or

wheat bread supplemented with PHGG .Study participants received each diet for three weeks

with a four week washout period. The PHGG-supplemented diet resulted in a Physiological and

Metabolic Functions for three weeks with a four week wash out period. The PHGG

supplemented diet resulted in a significant reduction of plasma levels of total cholesterol,

particularly LDL. There were no palatability issues and no serious side effects (Blake et al)

2.9. Yogurt Storage

Storage studies of yogurt have been done to study the time effect on sensory properties

bacterial feasibility as well as yogurt quality.

Salvador and Fiszman (2004) declared that value for firmness and textural analysis

showed constant trend but syneresis value was increased when yoghurt stored for 91 days at

10°C, 20°C for 21 days and 30 °C for 3 days. Rise in value of WHC and syneresis were due to

reorganizations in casein protein network.

As time goes on casein molecules reshuffle themselves into a more compact form that‟s

why its bonding strength is increased and its structure becomes thermodynamically more stable

because total free energy of the system is decreased. When rearrangements occur in casein

structure then gel network was also distorted and casein start to form new intersections as it is

proofed by variation in syneresis (Serra et al. 2009).

2.10. Effect on Rheological Properties during Storage

Gassem and Frank (1991) investigated on the yogurt prepared from milk treated with

enzymes (proteolytic) and reported rheological features of yoghurt prepared from it and

concluded that treated milk was immediately made into yogurt, which was stored at 7ºC and

analyzed after 1, 8 , and 15 days. Yogurt made from milk pretreated with microbial protease had

higher firmness, syneresis, and apparent viscosity than the untreated product. Yogurt made from

treated milk like with plasmin had clearly lower viscosity as well as lower firmness and syneresis

after storage of 8 days. Similarly yogurt made from treated milk like with protease had less water

holding capacity.

Salvador and Fiszman (2004) conducted a study of whole and skimmed flavored set-type

yogurt on textural and sensory properties during long term storage and reported that after long

term storage there was no significant change in acidity of yogurt. If compared whole and

skimmed milk under all storage conditions then firmness of whole milk was less than skimmed

milk yogurt. Flow properties of concentrated yogurt were affected by storage period at 8°C. High

viscosity value of concentrated yogurt showed that gel structure was well developed (Abu-Jdayil

and Mohameed, 2002).

Beal et al. (1999) investigated on both influence of culture conditions and storage time on

viscosity and acidification of stirred yogurt and accomplished by saying that viscosity

development prejudiced by many factors like incubation temperature, final fermentation pH, the

ratio of two Streptococcus thermophilus strains, acidification activity, post acidification and

texture and storage time on bacterial concentration and acidification development was affected

by strain association and temperature. There was a correlation between greater viscosity to lower

acidification activity which is showing that fermentation time affects the texture development.

By using the texturing strain of S. thermophilus, which required the longest fermentation time by

using low temperature and low final pH the most viscous yogurt was obtain.

Lee and Lucey (2004) studied the impression of structural breakdown and gelation

conditions on sensory and physical characteristics of stirred yoghurt and concluded that during

the shearing of intact gels, in low shear rate region there was an initial increase in apparent

viscosity because from intact network the resistance derived. Decreasing incubation temperature

and increasing milk preheating temperature lead to increase apparent and oral viscosity and

sensory mouth coating characteristics in stirred yogurt.

Akin and Konar (1999) studied the physical, chemical and sensory properties of flavored

yoghurt prepared from goat's and cow's milk and kept for 15 days of storage. They concluded

that titrateable acidity, pH, viscosity, protein, fat and total sugars values are significantly affected

by kind of milk used for yogurt preparation. Storage time too had great influence on these quality

features. Sensory characters including aroma, texture, appearance and color were influenced by

kind of milk but not affected with passage of time throughout storage. It was obvious from the

quality parameters that yogurt made with cow‟s milk was better than the goat‟s milk yogurt.

Previous studies showed that the addition of guar galactomannan in the preparation of

yoghurt is a positive influence on the rheological and textural properties. It also has a significant

effect on the growth of probiotic bacteria present in various fermented foods and finally have

immunological effects in humans. So, most of guar gum in fermented foods like yogurt, improve

the beneficial properties and nutritional profile.

Quality and Shelf Life of yoghurt

Shelf life of yoghurt is based on the, physical chemical, microbiological or sensory

characteristics. During storage changes in these qualities would be helpful in estimating the shelf

life of the product. Comparison of yoghurts that were stored at 10, 20 and 30°C was observed,

and tested for physical properties, sensory and microbiological analysis and found that syneresis,

appearance defects, atypical texture / mouth feel increased with storage time. The results also

indicated that combination of time and temperature is involved to bring out these changes

(Salvador and Fiszman, 2004).

CHAPTER-3

MATERIALS AND METHODS

The present Research work was carried out at Food Microbiology and Biotechnology Lab, National

Institute of Food Science and Technology (NIFSAT), University of Agriculture, Faisalabad

3.1 Procurement of Raw Material

Cow Milk was obtained from the commercial markets and guar gum was procured

from Ashraf Laboratories Limited, Faisalabad. Chemical, Reagents and Lab equipments used in

the research were made available from the Food Microbiology and Biotechnology Lab and Dairy

Lab of NIFSAT.

3.2 Compositional Analysis of Milk

The milk was analyzed for different parameters given below:

3.2.1. Fat content

The fat content of milk was determined by Gerber method as explained by Kirk and

Sawyer (1991).

a. Sulphuric Acid: A commercial grade sulphuric acid was used with the density of 1.815

± 0.002 g/mL at 20ºC.

b. Amyl Alcohol: Amyl alcohol of standard grade was used.

Eleven grams of milk sample was taken in a butyrometer also containing 10 mL H2SO4of

specific gravity 1.835 and 1mL amyl alcohol. It was then centrifuged for six minutes at 1100 rpm

and then the readings were noted.

3.2.2. Total solids

The percent residues called the total solids will be determined by drying the sample in hot

air oven according to method described in AOAC (2000).

A milk sample of (5g) was taken in a clean dried weighed crucibile and heated in water

bath for 15 minutes. Then it was kept in a hot air oven for 3 hours at 100 º C and cooled in a

dessicator for half an hour and weighed.

The percent residues will be calculated as under

Total Solids % = Residue after drying (g) x 100

Wt. of sample (mL)

3.2.3. Acidity

Acidity was determined by direct titration method No. 947.05 (AOAC 2000).

a. Phenolphthalein indicator

Phenolphthalein indicator was made by dissolving 1 g phenolphthalein in ethyl alcohol

(95% v/v) to a final volume of 100 mL.

b. N/10 NaOH

N/10 NaOH was made by dissolving 4 g of Sodium-hydroxide in distilled water and

makes the volume upto 1000 mL.

The phenolphthalein indicator is colorless in an acid solution but gives red color in an

alkaline solution. 10mL of well mixed and homogenous sample was taken in 100 mL flask. And

then 2-3 drops of phenolphthalein were added and titrated against 0.1 N NaOH till light pink

color was appeared. The volume of 0.1 N NaOH used was measured and then acidity was

calculated by following formula

Acidity % = 0.009 × N/10 NaOH used (mL) × 100

Wt. of sample (g)

3.2.4. pH

Negative logarithm of the hydrogen ion concentration is called pH. The pH provides

significant measurement as compared to titratable acidity..

The pH was directly measured by using the pH meter (WTW series pH-720). Adequate

quantity of sample of yoghurt ware taken in a beaker and adjusted to room temperature. The

electrodes of pH meter were calibrated in buffer solutions of pH 4 and pH 7 and then they were

immersed in the sample. Reading was noted after stabilization of pH meter

3.3. Partial Depolymerization of Guar Gum

The partial Depolymerization of Guar gum was done according to the method as described by

(Chauhan and Chauhan, 2009). Guar gum was depolymerized by treating it with a strong acid i.e

Hydrochloric Acid (Hcl).

Four Treatments of guar gum (GG) were depolymerised by treating them with a strong

acid (Hcl) for 1 to 4 hours respectively. 10 g of GG was taken in each 80 % aqueous methanol

solution also containing 5 % w/v Hcl in a conical flask and then the samples was stirred and

heated at 650 C for 1, 2, 3 and 4 hours respectively, resulting into four different fractions of

partially depolymerized guar gum based on time used for their depolymerization. The partially

Depolymerized guar gum was then washed methanol and then filtered with the help of a filter

paper(whatman grade 3). The samples were then freeze dried in lypholyzer to make them

incorporable in yogurt

3.4 Chemical analysis of Depolymerized Guar Gum

The depolymerized guar gum was analyzed for proximate composition i.e., moisture, fat,

crude fiber and ash content according to their respective methods as given below:

3.4.1 Moisture content

Hot air oven was used for the determination of moisture content of PDGG according to

the method no 44-15A, described in AACC (2000). 2 g sample was taken into pre weighed china

dish and was dried in an air forced draft oven at temperature of 105±5°C until constant weight of

matter was obtained. The moisture of the sample was determined as given below:

3.4.2 Fat content

The fat content of PDGG sample was determined by Soxhelt apparatus according to

AACC (2000) method No. 30-25. For this, petroleum ether extraction of 5g sample was done at a

Wt. of original sample – Wt. of dried sample x 100

Moisture (%) =

Wt. of original sample

condensation rate of 2-3 drops/sec for 8 hours. After distilling excess ether the residue of

extraction flask was dried at 100ºC for 30 min. Fat content was calculated by the formula as

below:

Crude Fat (%) = Wt. of fats x 100

Wt. of sample

3.4.3 Ash content

Ash is an inorganic residue left after the material is entirely burnt at a temperature of

550°C in a muffle furnace. It is an aggregate of all non-volatile mineral elements present in a

material as its oxides. The ash content of the PDGG was determined according to AACC (2000),

method No. 08-01. 5 g sample was taken in a pre-weighed crucible. The sample was Charred

over a flame burner until no smoke was set off and then moved it to a muffle furnace and ignited

at a temperature of 550°C until it changed into a grayish material. The residual contents of

sample was then cooled in a desiccator and weighed. The difference in weight between the blank

crucible and crucible with ash residue stated as amount of the original sample weight and

recorded as ash content.

Ash % = Weight of residue× 100

Sample weight

3.4.4 Crude fiber

The fiber content of guar samples was determined by following the procedure stated in AACC

(2000) Method No.32-10. 5g fat free and moisture free sample was boiled for 30 minutes in the presence

of 1.25 % H2SO4, and then filtered with muslin cloth. They were boiled again in 1.25 % NaOH for 30

minutes, and then filtered. The resultant residue was dried at 130 ºC for 2 hours and weighed. The dried

residual sample was ignited at 600ºC + 15ºC, cooled and reweighed. The crude fiber was calculated by

the formula given below.

Crude Fiber (%) = Loss in weight on ignition – blank x 100

Weight of sample

3.5 Yogurt Processing Steps

Yoghurt was processed in the Food Microbiology and Biotechnology Lab of National

Institute of Food Science & Technology, University of Agriculture Faisalabad according to the

process as explained by Stelio and Emmanuel (2004).

3.5.1. Filtration

Milk was filtered through a muslin cloth.

3.5.2. Standardization and Addition of PDGG

Milk was standardized and the all four acid treated treatments of PDGG were added in

the four different treatment of milk.

3.5.3. Pasteurization

After mixing, milk was pasteurized at 90 ºC temperature for a period of 15 minutes.

3.5.4. Homogenization

Milk was homogenized in a homogenizer to improve texture

3.5.5. Cooling

Milk was cooled to a temperature of 40-45 ºC.

3.5.6. Inoculation and Mixing

Inoculation and mixing was done with 2.5% of starter culture for the manufacturing of

yoghurt. A miscellaneous culture of Streptococcus thermophilus and Lactobacillus bulgaricus

was utilized.

3.5.7. Packaging

Then the inoculated milk was poured in cups of 300 mL volume and labeled.

3.5.8. Incubation

The inoculated milk was incubated at 37°C for about 3 hours resulting in 0.8-0.9% lactic

acid.

3.5.9. Storage

The yoghurt was then cooled to a temperature of 4-6°C to check further fermentation and

was subjected to sensory, physicochemical and physical evaluation.

Flow Diagram of Yoghurt Raw milk

Filtration

Standardization and addition of Guar Gum(1%)

(PHGG 1hr, 2hrs, 3 hrs, 4hrs)

Mixing

Pasteurization (700C for 30min)

Homogenization

Cooling (40-450C)

Inoculation

(Lactobacillus delbriieckii subsp. Bulgaricus and Streptococcus subsp. salivarius thermophillus

@ 2.5%)

Packaging

Incubation (370C-39

0C)

Cooling (150C-20

0C)

Storage (4-60C)

Fig. 3.1. Flow diagram of Yogurt

Table 3.1. Treatment combination for Analysis of yoghurt

Treatments Groups 0day 7th

day 14th

Day 21at

Day 28th

day

T0 Controlled - - -

T1 PDGG(1hr) - - -

T2 PDGG(2hrs) - - -

T3 PDGG(3hrs) - - -

T4 PDGG(4hrs)

*PDGG=Partially Depolymerized Guar Gum

3.6 Physicochemical Analysis of Yoghurt

The prepared yoghurt was analyzed for following parameters.

3.6.1. Total solids

The percent residues called the total solids were determined by drying the sample in hot

air oven according to method described in AOAC (2000).

A sample (5g) was taken in a clean dried weighed china dish and heated in a water bath

for 15 minutes. It was kept in a hot air oven for 3 hours at 100 º C and cooled in a desiccator for

half an hour and weighed.

Total Solids % = Residue after drying (g) x 100

Wt. of sample (mL)

3.6.2. Acidity

Acidity was determined by direct titration method No. 947.05 (AOAC 2000).

A well mixed sample homogenized yoghurt sample (10g) was taken in a china dish and

then it was diluted with 10 mL distilled water, 2-3 drops of phenolphthalein solution was added

as an indicator. After that it was titrated against N/10 NaOH until a slight pink color appeared as

an end point. The percent acidity (as lactic acid) was calculated as under,

Acidity % = 0.009 × N/10 NaOH used (mL) × 100

Wt. of sample (g)

3.6.3. pH

Negative logarithm of the hydrogen ion concentration is called pH. The pH provides

significant measurement as compared to titratable acidity..

The pH was directly measured by using the pH meter (WTW series pH-720). Adequate

quantity of sample of yoghurt ware taken in a beaker and adjusted to room temperature. The

electrodes of pH meter were calibrated in buffer solutions of pH 4 and pH 7 and then they were

immersed in the sample. Reading was noted after stabilization of pH meter

3.6.4. Water-holding capacity (WHC)

Water-holding capacity (WHC) of yogurt was determined by the procedure described by

Kalab et al. (1975). In this method yoghurt was centrifuged at 13500 rpm for 30 minutes at 10

ºC, drained of supernatant for 10 minutes, and the pellet weight determined. The water holding

capacity expressed as percent pellet weight relative to original weight of yoghurt.

3.6.5. Hardness

Hardness of yogurt gel was measured in the fermenting container by texture profile

analysis according to protocol specified by (Breene, 1975) with a rheometer. Hardness of yogurt

gel was measured inside in the fermenting container by texture profile analysis with a rheometer

using a cylinder plunger (16 mm), a compression rate of 5 mm/sec and 75% (22 mm)

deformation at 10ºC.

3.6.6. Viscosity

Viscosity of the yogurt was obtained by means of a Brookfield DV-I viscometer

(LVDVE 230) as described by (Gassem and Frank, 1991). Apparent viscosity was determined

on yogurt at 4-60C temperature. Spindle number 4 was used for this measurement with a rotation

of 60 rpm. Viscometer reading was noted in centipoise (CPS) unit.

3.6.7. Synersis

Synersis was measured by the method described by Peri et al (1985). The liberation of

watery-whey like liquid on the surface of the gel is termed as synersis. A set yoghurt sample of

450 g was placed at room temperature and left for two hours. The watery-whey like liquid was

siphoned off which then was taken in a graduated cylinder and measured.

3.7 Sensory Evaluation

All the frozen yoghurt samples was organoleptically rated for appearance, color, taste,

body/texture, flavor and overall acceptability by a panel of 5 judges(Trained penalisht from

NIFSAT) using a 9 point hedonic scale (Larmond, 1997). The questionnaire used for the purpose

is as under after statistical analysis.

3.8 Statistical analysis

The data obtained were subjected to statistical analysis using two factor factorial completely

randomized designs (CRD) according to the method described by Steel et al., (1997). Least

significant difference test (LSDts) was used to conclude statistically different groups.

Sensory Evaluation Performa

Hedonics Score System

9 points hedonic scale was follow for rating the sample.

Dislike extremely 1

Dislike very much 2

Dislike moderately 3

Dislike slightly 4

Neither dislike or like 5

Like Slightly 6

Like moderately 7

Like very much 8

Like extremely 9

Score Sheet:

Name of judge: ------------------

Signature: ------------------

Date: ------------------

Treatments Flavour Texture Taste Appearance Colour Overall

acceptability

T0

T1

T2

T3

T4

CHAPTER-4

RESULTS AND DISCUSSION

The current research work was designed to evaluate the effects of partially depolymerized

guar galactomannans on quality parameters of yogurt during storage. The cow milk for yogurt

preparation was taken from dairy farm and mixed with the four different treatments of partially

depolymerised guar galactomannas which were depolymerized at different time intervals (i.e. 1

hrs, 2 hrs, 3 hrs, 4 hrs) and were added with the concentration of 1% and inoculated with culture.

Milk was then pasteurized and cooled(40 0c) milk and filled in the plastic cups of 300ml and

placed in an incubator for incubation for 3-4hrs. After incubation yogurt was stored at 4-60C.

Physicochemical and sensory attributes of the product were studied at 0, 7, 21 and 28 days

during storage.

4.1 Compositional Analysis of Milk:

Raw milk was analysed for different parameters such as pH, acidity, fat, SNF and total

solids according to the methods of AOAC, 2000.

Table 4.1: Compositional analysis of milk

pH Acidity Fat % SNF % Total Solids %

6.8±0.04 0.10±0.07 4.6±0.08 8.30±0.12 12.90±0.14

4.2. Chemical compositions of Partially Depolymerized Guar Gum

The PDGG is a partially water soluble and a linear polysaccharide comprising of

Galactose and mannose units. The results regarding PDGG indicated that PDGG possessed 5.04

%, 4.87%, 4.53% and 4.61%, of moisture, 2.2%, 2.4%, 2.7 % and 2.1% crude fat, 2.6%, 1.9%,

1.7%, 2.1% ash and 2.2 %, 1.93 2.10%,and 1.85% crude fiber as given in the Table , respectively

for treatments T1, T2, T3 and T4. The present results regarding chemical composition of PDGG

are also in close agreement with the findings of Bhatty (1996) who demonstrated 2.3% ash

content of Guar Gum. The ash content (Table 5) found in the present study is also in close

conformity with the previous work of Burkus and Temelli (2005).

The fat content in the PDGG was found high as compared to reported by Faraj et al.

(2006) who found 0.05% lipids in high purity PDGG concentrate which might be due to less

impurity of PDGG in the present study. The Crude dietary fiber recorded during the present study is

also in consistent with the earlier findings of (Faraj et al, 2006).

Table 4.2: Chemical analysis of Partially Depolymerized Guar Gum

Treatment Moisture Crude Fat Ash Crude fiber

T1 5.04±0.08 2.2±0.18 2.6±0.14 2.22±0.15

T2 4.87±0.04 2.4±0.12 1.9 ±0.06 1.93±0.21

T3 4.53±0.14 2.7±0.17 1.7±0.27 2.10±0.10

T4 4.61±0.19 2.1±0.05 2.1±0.14 1.85±0.13 T1 = PDGG (1hr) T2 =PDGG (2hr)

T3= PDGG (3hrs) T4= PDGG (4hrs)

4.3. Yoghurt Analysis:

Yogurt was analyzed for physicochemical parameters such as pH, acidity, fat, synersis,

hardness, viscosity and water holding capacity and organoleptic features including color,

appearance, flavor, mouthfeel, texture and overall acceptability of the product. The evaluations

were performed at 0, 7, 14, 21 and 28 days during storage. Prepared yogurt was stored at 4-6oC

in plastic cups.

4.4. Physicochemical Analysis of Yoghurt:

4.4.1. pH:

Yogurt is a perishable dairy food commodity and susceptible to the environmental

conditions. The pH of the perishable commodities is decreased as the storage time increases and

the reduction in pH is due to the production of the acidity. The data on the changes of pH with

reference to storage time of yogurt prepared is presented in Table 4.3b while its statistical

evaluation is presented in Anova Table 4.3a showing that treatments and storage have a highly

significant effect on the pH of yogurt.

According to the mean comparisons table the pH of the yoghurt samples were decreased

as the storage time increased, the reason for this is the conversion of lactose into the production

of lactic acid. Increase in the value of pH from 0 to 28 day was 4.55 to 3.97, 4.55 to 4.10, 4.50 to

4.18, 4.56 to 4.28 and 4.46 to 4.28, for treatments To, T1, T2, T3 and T4 correspondingly.. The

treatment T1 showed high decreased in pH value during storage.

The statistical data showed that there were highly significant effects of storage period, treatments

and interactions of days with treatments. The decreases in the pH of present study is also in

conformity with the previous findings of Chandar et al. (1989) and Wofschoon et al. (1983)

declared that pH of yoghurt was decreased during storage.

Table 4.3a: Analysis of variance table for pH of yoghurt

** Highly Significant (P<0.05)

Table 4.3b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on pH of yogurt

Treatments

Days of Storage

Mean

0 7 14 21 28

To 4.55 4.43 4.22 4.17 3.97 4.26 d

T1 4.55 4.49 4.46 4.17 4. l0 4.33 c

T2

4.50 4.44 4.31 4.29 4.18 4.34 bc

T3 4.56 4.41 4.36 4.32 4.28 4.38 a

T4 4.46 4.46 4.38 4.33 4.28 4.38 ab

Mean 4.52 a 4.44 b 4.35 c 4.25 d 4.14 e

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 0.14 0.03 12.47**

Treatment 4 1.36 0.34 120.86**

Days×treatment 16 0.34 0.021 7.61

Error 50 0.14 0.002

Total 74 1.98

4.4.3. Acidity:

Acidity values are the values that express the total percentage of the production of lactic

acid. In all milk and milk products, the total titrateable acidity is produced by the conversion of

milk lactose into the form of lactic acid. As the storage time of the yoghurt increases the

production of lactic acid also increases with the help of bacteria that result into increase in the

value of acidity. The yoghurt that was stored for 28 days had apparently high value for acidity

than the yoghurt stored at beginning on 0th day. So with the addition of of partially

depolymerized guar galactomannans the acidity also increased with the passage of time but the

trend in increase was observed less than in controlled yogurt. Data regarding the acidity

variation with storage time was presented in Table 4.4b and its statistical analysis is shown in

Anove Table 4.4a for replication which showed that treatments and storage have a highly singnificant

effect of the acidity of yogurt

The mean values of acidity in the Table 4.4b represented that the acidity of all the

treatments increased during storage irrespective to different concentration of guar

galactomannans. Increase in the value of acidity from 0 to 28 day was 0.47 to 1.48, 0.42 to 1.03,

0.44 to 1.03, 0.43 to 1.13 and 0.42 to 1.13, for treatments To, T1, T2, T3 and T4 correspondingly.

Due to the production of lactic acid from milk lactose, acidity value of yoghurt

increased progressively. So maximum value for acidity of yoghurt was 1.48 for T0 and minimum

was 0.42 for T1. Soon the basis of this observation it was concluded that treatment with most

decreased acidity has more resistance against any changes, its mean the efficiency of

microorganisms remained controlled and the separation of the whey is also less. The reason for

this act is the addition of guar gum which has the power to stabilize the product during storage.

These findings agree with assumptions of Jogdand et al., (1991) and E.A. Khalifa, (2011)

in which the acidity increases with prolonged storage time. Chougrani et al., (2008), Gueimonde

et al. (2003) and Salvador and Fiszman (2004) also conclude that the acidity of yoghurt

increases with the increased storage period due to microbial activity and lactose change into

lactic acid.

Table 4.4a : Analysis of variance table for acidity of yoghurt

** Highly Significant (P<0.05) * Significant (P<0.05)

Table 4.4b: Mean Values of Effect of partially depolymerized guar galactomannans and

storage time on acidity (%) of yogurt

Treatments

Days of Storage

Mean

0 7 14 21 28

To 0.47 0.76 0.84 1.02 1.48 0.91 a

T1 0.42 0.61 0.75 0.91 1.03 0.74 b

T2 0.44 0.58 0.67 0.83 1.03 0.71 b

T3 0.43 0.55 0.68 0.87 1.13 0.73 b

T4 0.42 0.53 0.74 0.90 1.13 0.74 b

Mean 0.43 e 0.60 d 0.73 c 0.91 b 1.16 a

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 0.40 0.10 24.20**

Treatment 4 4.66 1.16 276.09**

Days × treatment 16 0.22 0.01 3.35*

Error 50 0.211 0.002

Total 74

4.4.4 Total solids

The percent residues after drying are called the total solids. The results pertaining to the

analysis of variance for the totals solids yogurt prepared with partially depolymerized guar

galactomannans is presented in table 4.5a and means values for total solids are presented in table

4.5b. Anova Table 4.5a for replication on total solids of yogurt suggested that treatments and

storage have a highly significant effect on total solids of yogurt.

The change in the total solids content of yoghurt is presented in the mean table 4.5b. The

changes in the total solids of yoghurt were 16.63 to 20, 13.90 to 16.33, 14.13 to 16.93, 15.47 to

18.23 and 15.53 to 17.33 for treatments T0 to T4 respectively during 28 days of storage. Total

solids of yoghurt ware increased within in treatments due to the addition of stabilizer. The lowest

value of total solids was observed in T1. Increase in total solids with storage days was due to

syneresis in yoghurt due to which water losses and solid content ratio increase. The results of the

current study are in accordance with Gassem and Frank, (1991) who reported that total solids were not

affected with the storage time of yoghurt. Similar results were also reported by Sodini et al., (2005) for

plain yoghurt when studying microstructure and physicochemical properties.

Table 4.5a : Analysis of Variance Table for Total Solids

Source DF SS MS F

Days 4 67.5288 16.8822 587.04**

Treatment 4 79.4636 19.8659 690.79**

Days*Treatment 16 4.0461 0.2529 8.79

Error 50 1.4667 0.0288

Total 74

** Highly Significant (P<0.05)

Table 4.5b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on Total solids of yogurt

Treatments

Days of Storage

Means 0 7 14 21 28

To 16.63 16.83 17.46 18.63 20 a 17.913 a

T1 13.90 14.30 14.96 15.30 16.33 14.96 e

T2 14.13 14.83 15.16 16.10 16.93 15.43 d

T3 15.46 15.86 16.60 17.26 18.23 16.68 b

T4 15.53 15.83 16.30 16.80 17.30 16.35 c

Means 15.13 e 15.53 d 16.1 c 16.82 b 17.76 a

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

4.4.5. Viscosity:

It is the resistance to flow measured in centipoise (cP). The factors which can affect the

viscosity include temperature, type, concentration and state of casein micells and fat globule size.

The most important is casein micelle which affects the viscosity in yogurt. Protein hydration can

also increase the viscosity. Viscosity is a factor used to determination the casein micelle

aggregation, texture and particle size distribution in yogurt (Ye, 2008)

Anova Table 4.6a for replication on viscosity of yogurt showed highly significant effect

of treatments and storage on the viscosity of yogurt containing partially depolymerized guar gum

with respect to control.

The viscosity of yoghurt increased during storage period of 28 days. The mean values for

viscosity were 1231 to 1581.7, 1676.7 to1866.7, 1890 to 2297.3, 1986.7 to 2387.3, 2204to

2624.7cps, for treatments of To, T1, T2, T3, T4, at 0, to and 28 days storage period correspondingly.

Control treatment (To) had lowest viscosity ranged from 1231to 1581.7cps. There was no

addition of any stabilizer in this treatment therefore it showed the lowest value of viscosity. In T1,

T2, T3 and T4 treatments, depolymerized guar galactomannans were used at the concentration of

1%.. With the addition of depolyermerized guar galactomannans, the viscosity of yogurt samples

was apparently increased from its initial values.. The statistical analysis showed that the results

were highly significant for the treatments and as well as for the storage days.

The outcomes of current work are in accordance with (Gassem and Frank (1991)

declared that yogurt viscosity was decreased as the storage time was prolonged. Farooq (1997)

showed the same results for decrease in viscosity over storage time for plain yoghurt. Olivera et

al. (1996) evaluated the various kinds of bacterial starter culture for the change in yogurt

viscosities during storage period.

Table 4.6a: Analysis of variance table for viscosity of yoghurt

** Highly Significant (P<0.05)

Table 4.6b: Mean values of effect of partially depolymerized guar galactomannans and

storage period on viscosity (cps)of yoghurt

Treatments Days of Storage

Means

0 7 14 21 28

To 1231 1369 1412 1516 1581.7 l 1421.9 d

T1 1676 1713.3 1800 1826.7 1866.7 1776.7 c

T2 1890 1946.7 2267.7 2264.3 2297.3 2133.2 b

T3 1986.7 1985.7 2127 2135.3 2387.3 2124.4 b

T4 2204 2360.3 2086.7 2336.7 2624.7 2322.5 a

Means 1797.7 d 1875 cd 1938.7 bc 2015.8 b 2151.5 a

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 7671653 1917913 161.74**

Treatment 4 1106098 276524 23.32**

Days × treatment 16 469223 29326 2.47**

Error 50 592901 11858

Total 74 9839875

4.4.6. Textural Analysis (Hardness)

The textural differences between the yogurts are attributed to the kind of milk used and

their compositional differences. Yogurt produced from bovine milk had a greater firmness than

caprine yogurt because it had the highest content of protein and total solids (Stelios and

Emmanuel, 2004).

. Anova Table 4.7a for Replication on hardness of yogurt clearly stated that treatments

and storage have highly significant effects over the firmness of the yogurt containing different

fractions of PDGG as compared to the control.

The data for the hardness of yoghurt under various treatments under storage is given in

Table 4.7b. Yogurt hardness was influenced significantly throughout storage time. Hardness value

for the control yoghurt (To) which was without galactomannans was 9.66 to 11.52 and 12.89 to

14.11, 13.17 to 14.41, 12.22 to 13.3 and 12.69 to 13.04 for T1, T2, T3, and T4, at 0, 7, 14, 21 and

28 days of storage respectively.

Control treatment (To) had lowest hardness ranged from 9.6 to 11.52. There was no

addition of stabilizer in this treatment therefore it showed the lowest value for hardness.. The

results declared significant variation in hardness value during storage but a little bit increase in it.

With addition of stabilizer, the hardness of yogurt samples was increased from its initial values.

And highly significant variation was examined among treatments and also in days for storage. The

statistical analysis showed that the results were highly significant for the treatments and as well

as for the days of storage.

The study of Fiszman and Salvador 2004; Fiszman et al. 1999; Gassem and Frank (1991)

support the current results who concluded that the increase in the total solids by the use of

functional dairy ingredients have a positive effect on the firmness of the set yogurt.

Table 4.7a: Analysis of variance table for hardness of yoghurt

** Highly Significant (P<0.05) * Significant (P<0.05)

Table 4.7b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on hardness of yogurt

Treatments Days of Storage

Means

0 7 14 21 28

To 9.66 10.6 11.35 11.48 11.52 10.92 c

T1 12.89 13.43 14.06 14.02 14.11 13.70 a

T2 13.17 12.97 13.25 13.70 14.41 13.50 a

T3 12.2 12.43 12.66 12.9 13.3 12.69 b

T4 12.69 12.91 12.85 12.86 13.04 12.87 b

Means 12.12 d 12.47 c 12.83 b 12.99 b 13.27 a

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 72.36 18.09 164.08**

Treatment 4 12.20 3.05 27.67**

Days × treatment 16 5.12 0.32 2.90*

Error 50 5.51 0.11

Total 74 95.20

4.4.7. Syneresis:

. Syneresis is the situation in which the gel will be shrinked and the whey water and

released serum was separated from the yoghurt. Syneresis was stated as volume per ml of whey

water separated from yoghurt. Syneresis is a main problem during the storage period of yoghurt.

Results related to the syneresis of yoghurt are presented in Table 4.8b.

The statistical results that were presented in the Anova Table 4.8a for replications

indicated that the Syneresis of control yoghurt had maximum value as compared to the other

treatments containing PDGG during days of storage. Regardless of the treatments, the highest

syneresis was found to be at day 28th and less syneresis was found at day 0, 7, 21 and 21st days of

storage. So it was found that there is a steady increase in syneresis in all the treatments with

increase in the storage period. There was an increase in syneresis for the controlled and the treated

samples were 1.83 to 3.86, 1.65 to 2.83, 1.7 to 3.23, 1.68 to 3.43, and 1.93 to 3.7, for treatments of

To, T1, T2, T3, and T4 at 0, 7, 14, 21 and 28 days of storage period correspondingly.

After 28 days storage period, highest values for syneresis observed in the control

treatment (To) in which guar gum was not incorporated. And the lowest value observed in the

treatment (T1) in which partially depolymerized guar galactomannans were added. Thus

statistical data that were represented in Table 4.6a showed that there was higly significant

influence of time of storage and all treatments on syneresis of yoghurt. These results were agreed

with the findings of Guven et al. (2005). Aryana and McGrew (2007) when studied the quality

characteristics of yoghurt with probiotics and Lactobacilli also found the steady increase in

syneresis with the storage time in all treatments. In another study Salvador and Fiszman (2004)

also reported increased synersis during storage when studied the textural characteristics of the

yoghurt.

Table 4.8a: Analysis of variance table for synersis of yoghurt

** Highly Significant (P<0.05)

Table 4.8b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on synersis (%) of yogurt

Treatments

Days of Storage

Means 0 7 14 21 28

To 1.83 2.3 2.8 3.2 3.86 2.8 b

T1 1.65 1.86 1.96 2.22 2.83 2.10 d

T2 1.7 2 .1 2.63 3.03 3.23 2.52 c

T3 1.68 2.76 3.06 3.23 3.43 2.83 b

T4 1.93 2.4 3.3 3.53 3.7 2.97 a

Means 1.75 e 2.26 d 2.75 c 3.04 b 3.41 a

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 7.11 1.77 72.85**

Treatment 4 25.33 6.33 259.36**

Days × treatment 16 2.58 0.16 6.61

Error 50 1.22 0.02

Total 74 36.25

4.4.8. Water Holding Capacity:

The data concerning water holding capacity of yoghurt under various treatments during

storage is shown in Table 4.9b. The mean value for water holding capacity of yogurt after 28

days of storage decreased from 54.94 to 42.96.

The mean values indicated that the water holding capacity of control yoghurt had

minimum value as compared to the other treatments during 28 days of storage. Highest water

holding capacity was found to be at 0 day and less water holding capacity was found at day 28th

days of storage. So it was found that there is a steady decrease in water holding capacity in all the

treatments with increase in the storage period.

The statistical analysis presented in Anova Table 4.9a for replications showed that the

decrease in water holding capacity highly significant for treatments as well as for storage time

and their interaction is significant. According to interaction the storage days and the product

found to be significant in case of water holding capacity. Water holding capacity value was

decreased from 39.93 to 27.9and 58.6 to 47.87, 63.56 to 50.63, 57.54 to 44.13, 54.53 to 42.53, for

the treatments of T1, T2, T3, and T4, 0, to 28 days storage correspondingly.

Results are in line with findings of Schorsch and Norton (2005) who declared decrease in

water holding capacity of yogurt during storage. Gassem and Frank, (1991) also found similar

results and reported decline in yogurt‟s water holding capacity during storage period.

Table 4.9a: Analysis of Variance Table for water holding capacity of yoghurt

** Highly Significant (P<0.05)

* Significant (P<0.05)

Table 4.9b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on water holding capacity (%) of yogurt

Treatments Days of Storage

Means 0 7 14 21 28

To 39.96 37.36 34.73 31.66 29.7 34.68 d

T1 58.6 58.16 54.13 52.06 47.83 54.16 b

T2 63.66 58.53 56.26 52.81 50.63 56.38 a

T3 57.96 52.44 48.16 46.83 44.13 49.90 c

T4 54.53 52.56 50.13 47.2 42.53 49.39 c

Means 54.94 a 51.81 b 48.68 c 46.11 d 42.96 e

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 4304.04 1076.01 610.35**

Treatment 4 1320.93 330.23 187.32**

Days × treatment 16 55.54 3.47 1.97*

Error 50 88.15 1.76

Total 74 5768.66

4.5. Sensory Evaluation

Sensory Evaluation of all samples of prepared yoghurt was done during the storage

intervals of 0, 7, 14, 21 and 28 days. Five judges were provided with printed Performa. The data

corrected of sensory evaluation for example color, appearance, flavor, mouth feel, body and

texture and overall acceptability were then processed for statistical analysis. These six

fundamental parameters associated with the quality and acceptability of dairy product and

yoghurt as affected by storage is discussed below.

4.5.1. Color:

The color of the product is also very important factor in relation to yoghurt. It is an

important quality attribute of a product. The data relevant to the mean scores for color of yoghurt

under various treatments during storage is shown in Table 4.10b.

The change in the sensory score of color during storage was 6.96 to 5.93 , 7.46 to 5.5.93,

7.16 to 5.36 , 7.03 to 5.30 , 6.90 to 3.30, for To, T1, T2, T3 and T4, correspondingly. In color

parameter there was significant differences among treatments and storage days as the main factor

that may influence the color of the product is the ingredients that were used in the

manufacturing of the product..T3 treatment obtained the highest score for the color character. In

this treatment PDGG was used which was treated for 3 hours. Many of the dissolved impurities

and matters removed after purification process. So therefore, guar galactomannans is a whitish

like product that does not impart its own color to the product to a greater extent as the days of

storage passed.

After storage color of yoghurt was found to be less effected and was acceptable which

ultimately improves the quality of yoghurt. With respect to statistical analysis of variance it was

concluded that the treatments and storage time are highly significant whereas the other

interactions was non-significant. Aryana and Paula McGrew, (2007) and Tarakci and Kucukoner,

(2003) reported similar results and found that there was no change in the color of the product

during storage.

Table 4.10a: Analysis of variance table for color of yoghurt

** Highly Significant (P<0.05)

Table 4.10b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on color of yogurt

Treatments

Days of Storage

Means 0 7 14 21 28

T0 6.96 7.13 6.53 6.23 5.93 6.56 a

T1 7.46 6.93 6.33 6.2 5.93 6.57 a

T2 7.16 6.86 6.16 5.83 5.36 6.28 b

T3 7.03 6.63 6.2 5.86 5.30 6.20 b

T4 6.90 5.86 5.36 4.63 3.33 5.22 c

Means 7.10 a 6.68 b 6.12 c 5.75 d 5.17 e

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 18.46 4.61 63.39**

Treatment 4 34.70 8.67 119.18**

Days × treatment 16 6.31 0.39 5.42

Error 50 3.64 0.072

Total 74 63.12

4.5.2. Appearance:

The appearance is one of the main characteristics in yoghurt that attract the consumers

and enhance the perceiving value of the food products. The data relevant to the mean scores for

appearance of yoghurt under various treatments during storage was shown in Table 4.11b.

The mean scores for appearance decreased during storage. The mean scores of

appearance in yoghurts after 28 days of storage were decreased from 6.9 to 4.16, 7.06 to 6.06,

7.13 to 5.06, 7.13 to 4.10, for To, T1, T2, T3 and.T3 got the lowest scores ranged from 4.1 at 28th

day.

After storage appearance of yoghurt was found to be effected and was not acceptable

which ultimately deteriorate the quality of yoghurt. With respect to statistical analysis of

variance it was concluded that the treatments and storage time are highly significant whereas the

other interactions was non-significant. Farooq and Haque, 1992 and Tarakci and Kucukoner,

(2003) reported similar results and found decrease in scores of appearance of yoghurt

throughout storage period. The consequences are in line with conclusion of Salwa et al. (2004)

who reported a reduction in appearance score of yoghurts during storage period.

Table 4.11a: Analysis of variance table for appearance of yoghurt

** Highly Significant (P<0.05)

* Significant (P<0.05)

Table 4.11b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on appearance of yogurt

Treatments Days of Storage

Means 0 7 14 21 28

To 6.96 6.43 5.93 5.13 4.16 5.72 c

T1 7.06 7.26 6.93 6.43 6.06 6.75 a

T2 7.60 7.13 6.83 6.40 6.06 6.80 a

T3 7.13 6.86 6.36 5.73 5.06 6.23 b

T4 7.13 6.43 5.60 4.96 4.10 5.64 c

Means 7.18 a 6.82 b 6.33 c 5.73 d 5.09 e

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 18.0 4.50 65.79**

Treatment 4 42.11 10.52 153.94**

Days × treatment 16 5.30 0.33 4.85*

Error 50 3.42 0.064

Total 74 68.84

4.5.3. Flavor

In sensory evaluation flavor of the product is the most important factor for determine

consumer's response. The flavor of yoghurt is due to the production of volatile compounds

through thermal breakdown of some constituents of milk in which one important aroma

producing compound is acetaldehyde.

The data on flavor of yoghurt under various treatments as effected by storage was shown

in Table 4.12b. The mean flavors scores after 28 days of storage were decreased from 7.53 to

4.7 for control yoghurt (To) and for treatments T1, T2 T3, and T4 scores decreased from 6.93 to

6.06, 6.90 to 5.11, 7.40 to 6.06 and 6.36 to 3.13 correspondingly... According to statistical

analysis findings of present study were highly significant for the treatments and storage period

but non-significant for the interaction between treatment and storage.

The decrease in flavor scores is related with the proteolytic activity of bacteria and the

production of higher activity (Abrahamsen, 1978) loss of flavor is attributed to fat and protein

degradation and minor development of sharp flavor produced by coliform bacteria, clostridiums

spp. and other organisms. The consequences were in line with results of Farooq and Haque,

1992: Tarakci and Kucukoner, 2001.They found a decrease in flavor of yoghurt during storage.

The results are also in line with Salwa et al., 2004 who reported a decrease in score of flavor of

yoghurts over storage time.

Table 4.12a: Analysis of variance table for flavor of yoghurt

** Highly Significant (P<0.05)

Table 4.12b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on flavor of yogurt

Treatments Days of Storage

Means

0 7 14 21 28

To 7.53 6.73 6.03 5.46 4.7 6.09 b

T1 6.93 7.06 6.70 6.2 6.06 6.59 a

T2 6.90 6.46 5.96 5.63 5.1 l 6.01 b

T3 7.40 6.93 6.56 6.20 6.06 6.63 a

T4 6.36 5.66 5.00 4.53 3.13 4.94 c

Means 7.02 a 6.57 b 6.05 c 5.60 d 5.01 e

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 39.58 9.89 90.63**

Treatment 4 52.28 13.07 119.71**

Days × treatment 16 10.11 0.63 5.79

Error 50 5.46 0.10

Total 74 107.44

4.5.4. Mouth Feel:

The data related to means of scores for mouth feel of yoghurt under various treatments

during storage was shown in Table 4.13b.

The mean taste scores of various yoghurts under preparatory treatments decreased during

storage. The mean taste scores after 0, 7, 14, 21 and 28 days for storage were decreased from

7.40 to 6.45, 6.60 to 3.66, 6.1 to 3.63, 6.66 to 4.66, 6.06 to 4.06, for To, T1, T2, T3 and T4,

correspondingly.

Minimum scores for mouth feel parameter in sensory evaluation was observed in the

treatment of T2. And highest were observed in the T0 treatment in which PDGG wasn‟t used. T3

and T4 treatments had better acceptability in its mouth feel parameter.

The statistical data revealed that the results were highly significant for treatments and

storage period and non-significant for their interaction shown in Table 4.11a. These results were

in favor of (Abrahamsen, 1978) who found that acidity development continued in yoghurt during

storage even at 6oC.

Table 4.13a: Analysis of variance table for mouth feel of yoghurt

** Highly Significant (P<0.05)

Table 4.13b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on mouth feel of yogurt

Treatments Days of Storage

Means 0 7 14 21 28

To 7.4 6.9 6.63 6.52 6.45 6.78 b

T1 6.60 6.10 5.56 4.56 3.66 5.30 c

T2 6.1 5.6 5.26 4.8 3.63 5.08 c

T3 6.66 6.1 5.73 5.6 4.66 5.75 a

T4 6.06 6.3 5.86 5.33 4.66 5.62 a

Means 6.54 a 6.2 b 5.81 c 5.37 d 4.61 e

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 39.58 9.89 90.63**

Treatment 4 52.28 3.07 119.71**

Days × treatment 16 10.11 0.63 5.79

Error 50 5.46 0.10

Total 74 107.44

4.5.5. Body and Texture In sensory evaluation, the body and texture of commodity is vital parameter. Texture

describes quality of the yoghurt and affects its mouth feel, appearance, and overall suitability

(Yoon, 2002).The data on body and texture score of yoghurt under various treatments during

storage was shown in Table 4.14b.

It is evident from statistical analysis of means that results were highly significant for

treatments and storage period and non-significant for their interaction. The mean body and

texture scores after 28 days of storage time decreased from 7.33 to 5.20, 7.13 to 5.86, 7.73 to

5.86, 7.30 to 5.76, 6.86 to 4.03, for the treatments of To, T1, T2, T3, and T4 correspondingly.

Body and texture of the yoghurt is influence by many factors including acidity and total

solids. This was due to less acidity and as well as due to low proteolytic activity in yoghurt

samples with less protein contents other than the plain yoghurt and increase in total solid

contents could be the second reason for higher body and texture score of yoghurt. The

consequences were comparable with findings of Farooq and Haque, 1992.They observed that

there was decrease in scores for body and texture of yoghurts throughout period of storage. The

consequences are agreed to Salwa et al. (2004) who reported a decrease in score of body and

texture of yoghurts during storage period.

Table 4.14a: Analysis of variance table for body and texture of yoghurt

** Highly Significant (P<0.05)

Table 4.14b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on body and texture of yoghurt

Treatments Days of Storage

Means 0 7 14 21 28

To 7.33 6.86 6.13 5.76 5.20 6.26 c

T1 7.13 7.5 7.00 6.23 5.86 6.74 a

T2 7.73 7.33 6.83 6.23 5.86 6.80 a

T3 7.30 6.96 6.56 6.13 5.76 6.54 a

T4 6.86 6.3 5.76 5.03 4.03 5.60 b

Means 7.27 a 6.99 b 6.46 c 5.88 d 5.34 e

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 14.41 3.60 29.00**

Treatment 4 37.46 9.36 75.38**

Days × treatment 16 3.00 0.18 1.51

Error 50 6.21 0.12

Total 74 61.10

4.5.6. Overall Acceptability:

The overall acceptability of the yoghurt is also a quality indicator of the product. The data

relevant to the mean scores for overall acceptability of yoghurt under various treatments during

storage was shown in Table 4.15b.

In overall acceptability parameter there were significant differences among treatments and

storage days. And non-significant differences observed in all other interactions. So the

organoleptic evaluation of overall acceptability of yoghurt was decreased from day 0 to day 28th

in all treatments. The mean values for overall acceptability was decreased from 7.66 to 4.06, 7.0 to

5.93, 7.5 to 5.93, 7.43 to 4.86, 6.56 to 4.06 for To, T1, T2, T3 and T4 at different days of storage at

0, 7, 14, 21 and 28 days correspondingly.

After storage overall acceptability of yoghurt was found to be decreased with the passage

of time. With respect to statistical analysis of variance it was concluded that the treatments and

storage time were highly significant whereas the other interactions was non-significant. Sarkar et

al. (1996) and Shahid Younus (2002) reported similar results and found that there is little bit

change in the overall acceptability of the product during storage.

Table 4.15a: Analysis of Variance Table for overall acceptability of yoghurt

** Highly Significant (P<0.05)

Table 4.15b: Mean values of effect of partially depolymerized guar galactomannans and

storage time on overall acceptability of yogurt

Treatments Days of Storage

Means 0 7 14 21 28

To 7.66 6.73 5.96 4.40 4.06 5.77 b

T1 7.0 7.13 6.8 6.30 5.93 6.63 a

T2 7.5 7.13 6.7 6.36 5.93 6.72 a

T3 7.43 6.76 5.8 5.30 4.86 6.03 b

T4 6.56 6.73 5.96 4.46 4.06 5.54 c

Means 7.23 a 6.89 b 6.24 c 5.37 d 4.97 e

To = Control (without galactomannans)

T1= PDGG (1hr) T2= PDGG (2hrs)

T3= PDGG (3hrs) T4=PDGG (4hrs)

Source DF SS MSS F value

Days 4 110.15 27.53 354.80**

Treatment 6 160.43 26.73 344.50**

Days × treatment 24 3.44 0.14 1.85

Error 70 5.43 0.07

Total 104 279.47

Chapter No 5 Summary

Milk is defined as the lacteal secretion, practically free from colostrums, obtained by the

complete milking of one or more healthy milking animals which contain not less than 8.25 % of

milk solids not fat and not less than 3.25% of milk fat. Yogurt” also known as thick milk” is a

fermented milk product which was initially done to increase the preservation of the milk.

Yoghurt is a wholesome food as it contains almost all the important nutrients that milk has and it

also provides it‟s consumers with probiotics. Milk is fermented into yoghurt and is mainly done

by two lactic acid producing bacteria like Lactobacillus bulgaricus and Streptococcus

thermophillus. These microbes help to develop not only characteristic flavor but also help the

consumer to improve their health

Fermented milk products such as yoghurt, increases the nutritional properties of the food

when we compared it with the original plain milk. Yoghurt has handsome amounts of vitamin A,

C and mineral contents like calcium, phosphorus etc. Apart from that yoghurt also have the

power to lower the blood cholesterol level, improve the formation mechanism of bones, retard

the growth of the cells of cancer and prevents coronary heart diseases with the help of lactic

acid micro flora. The behavior and aptitude of yoghurt when it is stored for a long time is very

important as the life of the yoghurt is based on whether the yoghurt display any physical,

chemical or sensory characteristics that are unaccepted for the consumption.

The current project was planned to determine the suitability and effect of partially

depolymerized guar gum on the storage stability of plain yoghurt and also to elucidate its effect

on the physicochemical and sensory properties of plain yoghurt. The PDGG was produced by the

partial depolymerization of guar gum by treating it with a strong acid. Guar gum acts as a good

stabilizer in this study as it reduces the problem of synersis in yoghurt which is a big problem in

the current scenario and also increases the shelf life and maintains the properties like flavor,

taste, improves texture of yoghurt and overall improves the quality parameters of yoghurt.

Partial depolymerization of guar gum is done to make its use easier in the fortification of

yoghurt. Partial Depolymerization doesn‟t affect the stability of the guar gum. So the PDGG

seems to decrease the synerisis, increase the water holding capacity and viscosity of the product,

finally increasing its shelf life and improving the texture.

Yoghurt was processed in five treatments, in the first treatment controlled yoghurt was

made without the addition of PHGG, in second treatment fraction of PDGG(1%) was added

which was depolymerized for 1 hour, in third treatment the fraction of PDGG was

depolymerized for 2 hours, and in fourth treatment PDGG was treated acidically for 3 hours

beforing adding in the yogurt and in the last treatment PDGG was added which was developed

after depolymerizing gua gum for 4 hours. And the treatments were given the names as T0 to T4.

All the treatments were stored at 4-60C for 15 days and then there physical, chemical,

microbiological and sensory characteristics analysis was done at 0, 5th

, 10th and 15

th days of

storage.

The results of the textural analysis showed a great response in the favour of treatments

containing PDGG in the yogurt as compared to the control treatment which was without any

stabilizing and emulsifying agent. Syneresis in yogurt is an important parameter of the yogurt

industry. Highest mean was observed in treatment T0 and T4 and the lowest mean was observed

in T1 and T2 which contain PDDG treated for 1 and 2 hours respectively in equal amounts. As total

solids decreases, the problem of higher syneresis occurs. The lowest mean for T1 was

comparable with the highest mean observed for control for syneresis of the yogurt which means

the addition of PDGG has a positive effect on controlling the syneresis during storage and best

treatment for controlling the syneresis was T1.

Similarly results of viscosity and firmness were observed as best for the yogurt

containing the PDGG as compared to the control having no stabilizing agent. A relationship was

observed in viscosity and addition of PDGG used in the processing of the yogurt. It can be

cleared by the means of T1 and T0 (1776.7 centipoises and 1421.9 centipoises respectively) that

the addition of PDGG had significant effect on the viscosity.

Sensory evaluation based on color, flavor, mouth feel, texture, firmness and overall

acceptability was conducted using 9-point hedonic scale (9 = like extremely; 1 = dislike

extremely). Colour and cutting were observed similar for al treatments. Whereas best scores

were attained by treatment containing guar gum , for surface appearance, Taste, flavor, mouth

feel, surface syneresis, texture, palatability and overall acceptability by the judges as compared

to the lowest rating of control treatment.

CONCLUSION:

It was concluded that partially depolymerized guar gum (PDGG) which were treated for

1 and 2 hours gave best results for physicochemical, and for the overall acceptability of plain

yoghurt. It was also observed that with the addition of PDGG the synersis in the yogurt was

reduced, and water holding capacity of the yogurt was also increased with the addition of PDGG,

it gave firm texture and body of yogurt, increased the viscosity and ultimately there was increase

in the shelf life of yoghurt.

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