Chapter 1 Introduction to Food Technology

FOOD TECHNOLOGY

(BNN 40304)

(Sem I, 2015/2016)

FAKULTI TEKNOLOGI KEJURUTERAAN

Dr. Noor Akhmazillah bt Mohd Fauzi

CHAPTER 1: Introduction to Food Technology

and Food Preservation

1.1 Industrial Revolution

1.2 Factors Affecting Food Technology

1.3 Principles Underlying Food Contamination

and Spoilage

1.4 Causes of Food Spoilage

1.5 Principles and Methods of

Food Preservation.

1.1 The Industrial Revolution….

The Industrial Revolution brought many technologies together, and provided new possibilities for investigation.

Mechanisation took place, increasing the volume of production of goods, including food products.

As more and more factories were built for massproduction of goods, so towns and cities grew andpopulations expanded. This also meant that therewere more people to feed.

A convergence of factors has made food

security one of the most important global

issues.

An increasing population wants a more

varied diet, but is trying to grow

more food on less

land with limited access to

water, all the time facing increased

costs for fertiliser, and

fuel for storage and

transport.

The world’s population is predicted to hit

9Bn by 2050, up from today’s total of

nearly 6.8Bn, and with it food demand is

predicted to increase substantially

More people die each year from hunger

and malnutrition than from AIDS,

tuberculosis and malaria combined, and

the World Bank estimates that cereal

production needs to increase by 50% and

meat production by 85% between 2000

and 2030 to meet demand

Put simply, the world needs to grow more food now.

Food Science?

Food Science is an applied science used to study the:

1. nature of foods

2. causes of their

deterioration

3. principles underlying

food processing

6

Food Technology?

Food Technology is the application of food science to the:

◦ selection

◦ preservation

◦ processing

◦ packaging

◦ distribution

◦ use of safe, nutritious, and wholesome food.

VS

Today, factors affecting food technology include:

a. domestication of animals and cropsb. preservation methodsc. development of villages and townsd. transport and travel e. warf. religion and cultureg. Famine (extreme scarcity of food).h. flood, disease

1.2 Factors Affecting Food Technology

Factors affecting food technology also include:

a.electricityb.discovery and use of raw materialsc.understanding of scientific principlesd.research and development of food

ingredientse.increasing technological capabilitiesf. economic understanding and trade

Discussion-30 min (section 1.1 & 1.2):

Work in pairs;How does technological capabilities can:

(i) increase food supply

(ii) improve food nutritional

…. share your points in the class

1.3 Principles underlying food contamination and spoilage

1. Approximately 1/3rd of all food manufactured in world is lost to spoilage/ contamination

2. Change in appearance, smell, or taste that makes it unacceptable to consumers, although not necessarily harmful to consumers.

3. There are 3 ways which food can be contaminated/spoiled:

(i) Physical

(ii) Chemical

(iii) Bacterial

(i) Physical contaminationThis can occur in a variety of ways at different stages of food processing and production. Some examples are:

• soil from the ground when harvesting;

• a bolt from a processing plant when packaging;

• a hair from a cook in the kitchen.

Care must be taken at each stage to prevent physical contamination.

(ii) Chemical contaminationThis can occur in a variety of ways at different stages of food processing and production. Some examples are:

• chemicals from the farm;

• a cleaning product used in the processing plant when packaging;

• fly spray used in the kitchen when preparing food.

Care must be taken at each stage of food production to prevent chemical contamination.

(iii) Bacterial contaminationAs soon as food is harvested, slaughtered or

manufactured into a product it starts to change. This

is caused by two main processes:

• autolysis – self destruction, caused by enzymes

present in the food;

• microbial spoilage – caused by the growth of

bacteria, yeasts and moulds.

Desirable food changes

Autolysis and micro bacterial changes are sometimes desirable(and are not referred to as spoilage), eg: enzymes cause fruit to ripen.

Here are some positive micro bacterial changes below.

Autolysis - enzymes

Enzymes are chemical compounds that are found in food.

They can cause food to deteriorate in three main ways:

• ripening – this will continue until the food becomesinedible, e.g. banana ripening;

• browning – enzymes can react with air causing the skinof certain foods, e.g. potatoes and apples discolouring;

• oxidation – loss of certain nutrients, such as vitamins A,C and thiamin from food, e.g. over boiling of greenvegetables.

Microbial spoilage(i) Bacteria• These are single celled micro-organisms (they cannot

be seen by the naked eye) which are present

naturally in the environment.

• There are many different kinds, some are useful, e.g. in

the production of yogurt, and some harmful.

• The presence of bacteria in food can lead to

digestive upset.

• Some bacteria produce toxins which can lead to this

also.

• Spores can also be produced by some bacteria

leading to toxins being produced.

• Yeasts are single celled fungi which can reproduce

by ‘budding’. This means that a small offshoot or

bud separates from the parent yeast cell.

• Yeasts can also form spores which can travel

through the air. These are easily killed by heating to

100ºC.

• In warm, moist conditions in the presence of sugar,

yeasts will cause foods like fruit to ferment producing

alcohol and carbon dioxide gas.

• Yeast is used in the production of bread and wine.

Microbial spoilage(ii) Yeasts

Yeasts

Spoil the taste of food but don't make it harmful

Grow on sugary foods.

Cannot grow at low temperatures

Cannot survive in sugar concentration above 50%

Cannot survive in vinegar

Are destroyed by temperatures above 70C

Microbial spoilage (iii) Mould

• Moulds are fungi which grow as filaments in food.

They reproduce by producing spores in fruiting

bodies which can be seen on the surface of foods.

• These fruiting bodies sometimes look like round furry

blue-coloured growths, e.g. mould on bread.

• Some moulds can be seen by the naked eye, e.g.

on bread.

Moulds

Are a type of fungus. They....

oSettle on food and grow into a visible plant which looks like fluff

oGrow on many foods including bread, cheese and meat.

oLike slightly acid conditions

oNeed moisture

oNeed warm temperatures between 20C and 40C

oAre destroyed above 70C

oCan survive in the fridge but not the freezer.

oMould on food means it is not very fresh and has been badly stored .Some moulds can make you sick or cause allergic reactions.

oSome moulds are used to give cheese its blue veins and to make quorn

Food spoilage• involves predictable succession of microbes• different foods undergo different types of spoilage

processes• toxins are sometimes produced algal toxins may

contaminate shellfish and finfish

We distinguish:• Perishable food: meats, fish, poultry, eggs, milk, most fruit

and vegetables• Semi-perishable food: potatoes, apples, nuts• Nonperishable food: sugar, flour, rice, dry beans

Related to water content (water activity) and implies storage conditions

ergotism

◦ toxic condition caused by growth of a fungus in grains

aflatoxins

◦ carcinogens produced in fungus-infected grains and nut products

fumonisins

◦ carcinogens produced in fungus-infected corn

Toxins

Food-Borne Infection◦ ingestion of microbes, followed by growth, tissue invasion, and/or release of

toxins

Food-Borne Intoxications◦ ingestion of toxins in foods in which microbes have grown

◦ include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning

Food-borne Illness

Examples of foodborne diseases (most are infections and associated with animal products):

Organism Number of cases

per year (U.S.)

Foods to watch

Campylobacter jejuni 1,963,000 Poultry and diary

products

Salmonella spp. 1,340,000 Poultry, meat, diary

and eggs

Clostridium

perfringens

248,000 Cooked and

reheated meat

products

Giardia lamblia 200,000 Contaminated meat

Norwalk-like viruses 9,200,000 Shellfish, other food

When food spoils, the following may change:

•appearance

• taste

• texture

• odour

Food may become unsafe to eat !!

1.4 Causes of food spoilageFood spoilage:

It means the original nutritional value, texture, flavour of the food

are damaged and the food become unsuitable to eat

1.4 Causes of food spoilage

Extrinsic parameters/factors

(i) Temperature

(ii) Relative humidity

(iii) Types and numbers of Microorganismsin the food

Micro-organisms are everywhere.

Micro-organisms can be carried by food,

people, dirty equipment, animals and pests.

Most are harmless.

What are micro-organisms?

Food poisoning is

caused by some of

these micro-organisms.

These are called food

poisoning bacteria.

There are beneficial uses of some micro-

organisms.

• Bread dough – raising agent

• Yogurt making - fermentation

Intrinsic Factors Affecting Microbial Growth

Micro-organisms need conditions to survive and

reproduce these can include:

• Temperature

• Moisture

• Food

• Time

• Oxygen

• pH level

Factors of bacterial growth(i) Temperature

1. Bacteria need warm conditions to grown and multiply.

2. The ideal temperature for bacterial growth is 30ºC – 37ºC.

3. Some bacteria can still grow at 10ºC and 60ºC. Most bacteria are destroyed at temperatures above 63 ºC. Bacterial growth danger zone in 5ºC - 63ºC.

4. At very cold temperatures, bacteria become dormant – they do not die, but they cannot grow or multiply.

100ºC: Water boils

82ºC: Core temperature of hot food

5ºC - 63ºC: Danger zone for rapid growth

of micro-organisms

1ºC - 4ºC: Temperature of fridge

0ºC: Freezing point of water

-18ºC: Temperature of freezer

(i) Temperature

(ii) Moisture

Where there is no moisture bacteria cannot grow. However, bacteria and moulds can both produce spores which can survive until water is added to the food.

(iii) Food

Bacteria need a source of food to grow and multiple, these food usually contain large amounts of water and nutrients.

(iv)Time

One bacterium can divide into two every 20 minutes. Food where bacteria rapidly multiple in are called perishable foods.

Factors of bacterial growth

(v) Oxygen

Some bacteria need oxygen to grow and multiply.

These are called aerobic bacteria. Other bacteria

grow well when there is no oxygen present, these are

known as anaerobic bacteria.

(vi) pH level

An acidic or alkaline environment can promote of

inhibit microbial growth. Most bacteria prefer a neutral

pH (6.6 – 7.5). Moulds and yeasts can survive at pH

levels of 1-1/5 (very acidic), food spoilage usually

occurs by yeast and moulds.

Factors of bacterial growth

Food (and water)

• The type of food is important.

• Ready to eat foods, such as cooked meat and

chicken or dairy foods, can support the growth of

microbes.

• They need to be stored properly, e.g. chilled.

• Dried foods – these do not have water, so the micro-

organisms cannot grow, e.g. dried milk, instant soup

mix.

• Pickles and jams – these contain vinegar or sugar

which stop the micro-organisms from growing.

The risk of food poisoning can be minimised through:

•good food safety;

•good hygiene procedures.

Store food in the right place

•Check labels for where they should be stored.

•Check date marks on food labels.

•Do not leave foods out – they could get warm or be contaminated with

microbes from an insect or pest.

Prepare and cook food hygienically

•Get ready to cook – hands, aprons …

•Prepare raw foods away from cooked foods – do not mix up.

•Cook foods thoroughly, e.g. no raw areas in roast chicken.

•Clean up and be tidy all the time.

Pop Quiz in Pairs (Section 1.3 & 1.4):

(i) Identify the three methods of food contamination.

(ii) Distinguish between the two different food changes,

through autolysis and micro-organisms.

(iii) Briefly explain the positive food changes.

(iv) Identify the conditions which promote bacterial growth.

1.5 Principles and methods of food preservation.

Principles of Food Preservation

• A good method of food preservation is one that slows down or prevents altogether the action of the agents of spoilage.

• Also, during the process of food preservation, the food should not be damaged

• In order to achieve this, certain basic methods were applied on different types of foods.

Thus; preservation is the treatments which are given to food products so asto increase their longevity and stop or slow down their spoilage ofnutritional value. It prevents the growth of bacteria, yeasts, fungi and othermicro-organisms and also retards the oxidation of fats which causerancidity.

Principles of Food Preservation

1. Removal of micro-organisms or inactivating them: This is done by removing air, water (moisture), lowering or increasing temperature, increasing the concentration of salt or sugar or acid in foods.

2. Inactivating enzymes: Enzymes found in foods can be inactivated by changing their conditions such as temperature and moisture, when you preserve peas, one of the methods of preservations is to put them for a few minutes in boiling water. This method also known as blanching inactivates enzymes and thus, helps in preserving the food.

3. Removal of insects, worms and rats: By storing foods in dry, air tight containers the insects, worms or rats are prevented from destroying it.

ControlControl of

microorganisms

• Heat

• Cold

• Drying

• Acids

• Sugar and salt

• Oxygen concentration

• Smoke

• Radiation

• Chemicals (preservatives)

Control of enzymes

• Heat

• Oxygen removal

• Acids

• Chemicals

Control of other Factors

• Protective packaging

• Sanitation

Methods for preserving food

Physical methods

• Vacuuming

• Freezing

• Drying

• Burial

• Smoking

• Pasteurization

• Canning

Chemical methods

• High salt and high sugar

• Citric acid and ascorbic acid

• Antioxidants

1) Thermal Process (application of heat)• Application of heat• Inactivate enzymes• Kill microorganism- Most bacteria are killed at 82-93°C, but spores

are not.• 121°C wet heat for 15 min is required to ensure sterility• High acid foods require less heat • Pasteurization eliminates only disease causing microorganisms in

milk

Preservation methods

Various methods Hot air: baking, roasting

and drying

Hot oil:frying

Irradiated energy: microwave, infrared radiation, ionizing

radiation

Hot water/steam:Cooking, blanching, pasteurization, sterilization,

evaporation, extrusion

Principles of thermal processing:

• The concept of thermal processing, which primarily involves in-container sterilization of foodstuff has come a long way since Bigelowand Ball developed in 1920, the first scientific basis for calculating theminimum safe sterilization process

• In all its forms of application, thermal processing persists as the mostwidely used method of preserving and extending the useful shelflifeof foods

• The concept of in-container sterilization (canning) involves theapplication of a high-temperature thermal treatment for asufficiently long time to destroy microorganisms of public health andspoilage concerns

• Industrially, thermal processes are designed by processing authoritiesto provide commercially sterile or shelf-stable products.

• Foods have different microorganism or enzymes that the thermalprocess is designed to destroy

• In order to determine the type of microorganism the process shouldbe based on, several factors must be considered:

(1) Oxygen sensitivity1. In foods that are packaged under vacuum in hermetically sealed

containers, low oxygen levels are intentionally achieved2. Therefore, the prevailing conditions do not support the growth of

microorganisms that require oxygen (obligate aerobes) to results infood spoilage or public health problems

3. Further, the spores of obligate are less heat resistance than themicrobial spores that grow under anaerobic conditions (facultativeor obligate anaerobes)

Class Description Examples

Obligatory aerobes Requires oxygen to grow Most moulds, Micrococcus, serratiamarcescens,Mycobacteriumtuberculosis

Obligatory anaerobes Require absence of oxygen to grow

C. botulinum, C. sporogenes, C. thermosaccharolyticum

Facultative anaerobes Can grow in the complete absence or presence of only small amounts of oxygen

B.coagulans, Staphylococcus aureus

Classification of microorganism based on their oxygen sensitivity

(2) pH1. The growth and activity of microorganism are also largely pH

dependent2. For a thermal processing standpoint, foods are divided into 3 major

pH groups

Group pH Examples

High acid <3.7 Fruit juices, apples, berries, cherries (red sour), plums, sour pickles, vinegar

Acid or medium acid

3.7 -4.5 Fruit jams, fruit cocktails, grapes, tomatoes, tomato juices, peaches, pineapples, potato salad, prune juice

Low acid 4.5 All meat, fish, vegetables, mixed entries and most soups

1. Most lab. dealing with thermal processing devote special attentionto C. botulinum, which is a highly resistant, rod-shaped, spore-forming, anaerobic pathogen that produces the botulism toxin

2. The mere presence of the pathogen alone in a product does notconstitute a health hazard; however, concern in this respect iswarranted if the spores find favorable conditions in the container togerminate and produce a deadly botulism toxin.

3. It has been generally accepted that C. botulinum does not grow andproduce toxin below a pH of 4.6

(3) Temperature

In microbiology, D-value refers to decimal reduction time and is the time required

at a given temperature to kill 90% of the exposed microorganisms.

Thermal resistance of microorganism

Calculating the D-Value

This seems like a really complex question but it's very simple

Our D-value is 3 minutes, the time it takes to kill 90% of our sample at a certain temperature

in our autoclave. We started with 1,000,000 microbes and we are left with 10 at the end

Now, using the following equation we can plug those numbers into it.

The equation reads that:

The D-Value = (Total Heating Time)/(log (Original Population) - log(Remaining

Population))

In our case, the equation would be:

3 = (X)/(log(1,000,000) - log(10))

By solving for X we find out that the total heating time is 15 minutes. Meaning, with a D-value

of 3 minutes we'd reduce our microbial population from 1,000,000 to 10 in 15 minutes flat at

the temperature the autoclave specifies.

Log N2 – Log N1 = -t/DLog (N2/N1) = -t/DN2/N1 = 10^(-t/d)

Log N2 – Log N1 = -t/DLog (N2/N1) = -t/DN2/N1 = 10^(-t/d)

4.1 minutes

Z-value is a term used in microbial thermal death time calculations. It is the

temperature required for one log10 reduction in the D-value.

Thermal death time is a concept used to determine how long it takes to kill a

specific bacteria at a specific temperature.

The Z-value is the increase or decrease in temperature required toreduce or increase the decimal reduction time by one decimal. It is ameasure of the change in death rate with a change in temperature.

Z = (T2-T1)/(logD1-logD2)

Where T = temperature and D = D-value

2. Refrigeration (Removal of heat)

• Lowering temperature of food • Decreases the rate of enzymatic, chemical and microbial reactions in food• Storage life is extended

Freeze dry

Freezing

Various methods Chilling

3. Control of water content (drying)

• Microorganisms require free water• Free water is removed from the food and therefore,

is unavailable to microbial cells• Multiplication will stop• Water unavailable for chemical/biochemical reactions• Storage life extended

Physical removal of water from food (dehydration)

Addition of substance that bind water in food, making it

unavailable (sugar, salts)

Removal of some water from food (concentration)

• Dehydrating food also dehydrates the microorganisms• Microorganisms contain aprrox. 80% of moisture• Freeze-drying (lyophilization) is the most efficient method

Various methods Under the sun

4. Radiation

• Ionizing radiation• Inactivate microorganisms in food• Destroy storage pests• Inactivate enzymes

Various methods

Infrared radiation

Ultraviolet radiation

5. Atmosphere composition

• Removal of oxygen• Inhibits o2-dependant enzymatic and chemical reactions• Inhibits growth of aerobic microorganisms

Various methods

Paraffin wax

Nitrogen back flushed bags (potato chips)

Controlled atmosphere storage

Vacuum packaging of fresh food (cured meats)

• Exclude air for control of aerobic microorganisms• Provide air for control of anaerobic microorganisms• Add carbon dioxide and nitrogen• Application of Modified Atmosphere or Controlled Atmosphere packaging• Most of fruits and vegetable give off ethylene gas• Ethylene accelerate ripening process• For extension of shelf-life it should be removed

6. Fermentation

• Specific microorganisms are used (starter cultures)• Facilitate desirable chemical changes • Longer storage life• Produce acids, alcohol that will prevent growth of undesirable microorganisms• Produce antimicrobial substances

7. Addition of chemicalsVarious chemicals used are -

a. Acids (inhibit microbial growth and enzymatic reactions)b. Organic acids (acetic, citric, tartaric acids)c. Inorganic acids (hydrochloric, phosphoric acids)d. Food grade, comply w/regulations e. Antioxidants (to delay oxidative rancidity)

Antimicrobial agents: o sodium propionate (mould inhibitor)o sodium benzoate (antibacterial)o sugar and salt (high concentrations)

8. Smoke• The combination of heat, to dry food without cooking it

and the addition of aromas, from the smoke preserves the food

• Heat also helps destroy microorganisms• Heat dries the food• Contains preservative chemicals (eg. formaldehyde) from

the burning wood

9. Curing (Salt and Sugar)

• Salt binds with water molecules and thus acts as a dehydrating agent in foods.

• Impair the conditions under which pathogens cannot survive• Curing is used with certain fruits and vegetables.• Meats can be submerged in a salt solution known as brine

• One of the oldest preservation methods• Addition of either to a food item increases the affinity of

the food for water• Decreases Aw in the food• Removes water from the microorganisms through osmosis

PRESERVATION BY USING CHEMICALS

A preservative is defined as only substance which is capable of inhibiting, retarding or arresting the growth of microorganisms.

Microbial spoilage of food products is also controlled by using chemical preservatives. The inhibitory action of preservatives is due to their interfering with the mechanism of cell division, permeability of cell membrane and activity of enzymes.

Pasteurized squashes, cordials and crushes have a cooked flavour. After the container is opened, they ferment and spoil within a short period, particularly in a tropical climate. To avoid this, it is necessary to use chemical preservatives.

Chemically preserved squashes and crushes can be kept for a fairly long time even after opening the seal of the bottle. It is however, essential that the use of chemicals is properly controlled, as their indiscriminate use is likely to be harmful.

The preservative used should not be injurious to health and should be non-irritant. It should be easy to detect and estimate.

Two important chemical preservatives are permitted to

(i) Sulphur dioxide

• It is widely used throughout the world in the preservation of juice, pulp, nectar, squash, crush, cordial and other products.

• It has good preserving action against bacteria and moulds and inhibits enzymes, etc.

• In addition, it acts as an antioxidant and bleaching agent.

• These properties help in the retention of ascorbic acid, carotene and other oxidizable compounds

• It also retards the development of nonenzymatic browning or discolouration of the product

• It is generally used in the form of its salts such as sulphite, bisulphate and metabisulphite.

• Potassium metabisulphite (K2O 2So2 (or) K2S2O5) is commonly used as a stable source of So2.

• When added to fruit juice (or) squash it reacts with the acid in the juice forming the potassium salt and So2, which is liberated and forms sulphurous acid with the water of the juice

• SO2 has a better preservative action than sodium benzoate against bacteria and moulds. It also retards the development of yeasts in juice, but cannot arrest their multiplication, once their number has reached a high value.

• The concentration of So2 required preventing the growth of mirgroorganism at different pH levels are as under.

• The toxicity of So2 increases at high temperature. Hence its effectiveness depends on the acidity, pH, temperature and substances present in fruit juice

The advantages of using So2 are

a) It has a better preserving action than sodium benzoate against bacterial fermentationb) it helps to retain the colour of the beverage for a longer time than sodium benzoatec) being a gas, it helps in preserving the surface layer of juices alsod) being highly soluble in juices and squashes, it ensures better mixing and hence their

preservation ande) any excess of So2 present can be removed either by heating the juice to about 71o C or

by passing air through it or by subjecting the juice to vacuum. This causes some loss of the flavouring materials due to volatilization, which can be compensated by adding flavours.

Disadvantages (or) limitations

a) It cannot be used in the case of some naturally coloured juices like those pomegranate, strawberry, coloured grapes, plum etc. on account of its bleaching action.

b) It cannot also be used for juices which are to be packed in tin containers because it not only corrodes the tin causing pinholes, but also forms H2S which has a disagreeable smell and reacts with the iron of the tin container to form a black compound, both of which are highly undesirable and

c) So2 gives a slight taste and colour to freshly prepared beverages but these are not serious defects if the beverage is diluted before drinking.

(ii) Benzoic acid

1. The antibacterial action of benzoic acid is increased in the presence of Co2 and acid e.g. Bacillus subtilis cannot survive in benzoic acid solution in the presence of Co2.

2. Benzoic acid is more effective against yeasts than against moulds. It does not stop lactic acid and acetic acid fermentation.

3. The quantity of benzoic acid required depends on the nature of the product to be preserved, particularly its acidity. In case of juices having a pH of 3.5-4.0, which is the range of a majority of fruit juices, addition of 0.06 to 0.10% of sodium benzoate has been found to be sufficient.

4. In case of less acid juices such as grape juice at least 0.3% is necessary. The action of benzoic acid is reduced considerably at pH 5.0.

5. In the long run benzoic acid may darken the product. It is, therefore, mostly used in coloured products of tomato, jamun, pomegranate, plum, watermelon, strawberry, coloured grapes etc

Review Questions (Section 1.5):

(i) Provide two methods for preserving foods.

(ii) List the methods classified in (i)

(iii) Identify three reasons food gets spoilt

(iv) Briefly explain the advantages of preserving foods

a) Drying- It is an ancient technique which reduces water activity sufficiently to prevent or delay bacterial growth.

b) Refrigeration- In this process food is preserved by slowing down the growth and reproduction of microbes and the action of enzymes which cause food rotting.

c) Freezing- It is one of the common preservation process used for preserving food items which do not require freezing when unprepared.(in unprepared state).

d) Vacuum Packing- It is done in airtight bag or bottle. It removes the oxygen needed for the survival of bacteria. It is mostly used for storing nuts.

e) Salting- It withdraws the water from the food product, and hence is used as a preservation technique.

f) Sugaring- It is used to preserve fruits such as apples, pears, peaches and apricots etc.

g) Artificial Food Additives- Commonly used food additives are calcium propionate, sodium nitrate, sodium nitrite, sulfites and disodium EDTA which are used as antimicrobial agents.

h) Pickling- In this method food is preserved as an anti-microbial liquid which inhibits or kills bacteria and other micro-organisms. The typical pickling agents include brine, vinegar, alcohol, and vegetable oils. Sometimes chemicals are also added such as sodium benzoate and EDTA which enhance the shelf life of the food.

i Lye- The chemical sodium hydroxide is known as lye and it is often added to food for its preservation as it makes the food alkaline and prevents bacterial growth, it also saponifies the fat in the food and changes its flavor and texture.

j) Canning And Bottling- It involves the sealing of cooked food in sterile jars and bottles and boiling the container to kill or weaken any other form of microbes.

k) Jellying- It is the cooking of food in a material which solidifies it in the form of gel, such as gelatin, agar, maize flour, and arrowroot flour.

l) Potting- Mainly used for meat, by setting it in a pot and sealing it with a layer of fat.

m) Irradiation- It is the exposure of food to ionizing radiation; either high energy electrons or X-rays or by gamma rays. This treatment kills bacteria, molds and insect pests, reduces ripening and spoiling of fruits and also induces sterility.

n) Pulsed Electric Field Processing- It is a method of preservation by strong electric field.

o) Modified Atmosphere- It is a way of preserving food by operating on the atmosphere around it and sometimes the oxygen content is lowered and the carbon content is increased which prevents from insects and molds. Also nitrogen gas is used to kill bacteria effectively.

Review Questions (Section 1.3):

(i) Provide two methods for preserving foods.

(ii) List the methods classified in (i)

(iii) Identify three reasons food gets spoilt

High content of water

Activity of food enzymes

Reaction with oxygen

(iii) Briefly explain the advantages of preserving foods