Lipids: Functions, Applications in Food Industry and Oxidation

American Journal of Food Science and Nutrition Research 2016; 3(6): 162-171

http://www.openscienceonline.com/journal/fsnr

ISSN: 2381-621X (Print); ISSN: 2381-6228 (Online)

Lipids: Functions, Applications in Food Industry and Oxidation

Abdelmoneim H. Ali1, 2, *

, Sherif M. Abed1, 3

, Sameh A. Korma1, 2

, Hamada M. Hassan2

1State Key Laboratory of Food Science and Technology, Synergetic Innovation Center of Food Safety and Nutrition, School of Food Science

and Technology, Jiangnan University, Wuxi, China 2Department of Food Sciences, Faculty of Agriculture, Zagazig University, Zagazig, Egypt 3Food and Dairy Sciences and Technology Department, Faculty of Environmental Agricultural Science, Suez Canal University, El Arish,

Egypt

Email address

[email protected] (A. H. Ali) *Corresponding author

To cite this article Abdelmoneim H. Ali, Sherif M. Abed, Sameh A. Korma, Hamada M. Hassan. Lipids: Functions, Applications in Food Industry and

Oxidation. American Journal of Food Science and Nutrition Research. Vol. 3, No. 6, 2016, pp. 162-171.

Received: August 19, 2016; Accepted: August 29, 2016; Published: September 9, 2016

Abstract

Lipids are a group of naturally occurring molecules that includes fats, waxes, monoglycerides, diglycerides, triglycerides,

phospholipids, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), and others. The basic biological roles of lipids

include energy storage, signaling, and acting as structural components of cell membranes. Lipids have many applications in the

cosmetic and food industries as well as in nanotechnology. Lipids are very different in both their individual compositions and

functions. These diverse compounds that make up the lipid family are so grouped because they are insoluble in water. They are

however soluble in other organic solvents such as ether, acetone, and other lipids. This review is focused on some basic points

of lipids such as the difference between docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), the role and function

of lipids and their applications in food industry. Moreover, it presents the mechanism of lipids oxidation, and how to measure

and prevent the oxidation of lipids.

Keywords

Lipids, Functions, Applications, Oxidation, Antioxidants

1. Introduction

Lipids are defined on the basis of their solubility

characteristics, not primarily their chemical composition. The

term “lipids” is defined as those organic molecules that are

insoluble in water, soluble in organic solvents (e.g.,

chloroform, methanol, ether), contain hydrocarbon groups as

primary parts of the molecule, and are exist in or derived

from living organisms [1]. Compound classes covered in this

definition or classification include fatty acids (FAs),

acylglycerols, fatty acids esters (e.g., waxes), and isoprenoid

hydrocarbons. Further compounds also included are regularly

considered as belonging to different classes, such as

carotenoids, sterols, and the vitamins A, D, E, and K. Lipids

tend to be categorized as “simple” or “complex,” referring to

the size or structural detail of the molecule. The group of

simple lipids includes fatty acids, hydrocarbons, and

alcohols, all of which are comparatively “neutral” in terms of

charge. While complex lipids, for instance glycolipids and

phospholipids, are relatively more charged and are also

referred to as “polar.”

Fats and oils are fractions of lipids, mainly composed of

triglycerides with great importance in food systems, and they

are formed through the esterification of fatty acids molecules

with one molecule of glycerol [2-5]. Lipid oxidation is one of

the major reasons of quality retrogradation in natural and

processed food products. Oxidative retrogradation is a large

economic issue in the food industry because it affects many

quality parameters such as flavor (rancidity), texture, color,

and the nutritive value of foods. Furthermore, it results in the

production of potentially poisonous compounds [6]. Lipid

American Journal of Food Science and Nutrition Research 2016; 3(6): 162-171 163

oxidation considered very significant to food producers

particularly in the case of increasing the content of

unsaturated lipids in the final products in order to improve

the nutritional profiles. Consequently, lipid oxidation is one

of the major factors that limit the shelf life of foods. In

addition, the oxidative instability of the polyunsaturated fatty

acids frequently limits their applications as nutritionally

beneficial lipids in functional foods production.

2. The Differences Between DHA and

EPA

2.1. DHA: Docosahexaenoic Acid (22:6n-3)

Fig. 1 shows the structure of docosahexaenoic acid (DHA).

It is produced de novo by marine algae and is a primary

component of fish oil (approximately 8- 20% by weight).

DHA production in animals from linolenic acid occurs

through the desaturation/elongation of β-linolenic acid to

24:5n-3. This very long chain unsaturated fatty acid is

desaturated by a ∆6 desaturase (possibly a unique ∆6

desaturase enzyme) and the resulting fatty acid undergoes

one cycle of β-oxidation to form DHA. Animals seem to have

a requirement for DHA for neural function, and they depend

on the production of this fatty acid from n-3 precursors by

elongation/desaturation cycles or through ingestion of the

intact acid. Although the exact role DHA plays in animal

physiology is not clear, the great care with which the fatty

acid is preserved in certain tissues implies that it may be an

essential component of certain cells. Brain and retinal tissues

are predominantly enriched in DHA.

Fig. 1. Docosahexaenoic acid.

2.2. EPA: Eicosapentaenoic Acid (20:5n-3)

Eicosapentaenoic acid (EPA) is produced de novo by

marine algae and in animals by the desaturation/elongation of

α-linolenic acid. EPA is the primary fatty acid of fish oil

(about 25-20% by weight) although it is not produced de

novo by fish. It has also been reported that significant

production of EPA can take place in animals through the β-

oxidation chain shortening of DHA. EPA has been widely

investigated for its action as a competitive inhibitor of

arachidonic acid metabolism. Although eicosanoids can be

produced from EPA, they appear to have either no activity or

an activity that opposes arachidonic acid–derived

eicosanoids. The chemical structure of EPA is presented in

Fig. 2.

Fig. 2. Eicosapentaenoic acid.

3. Types and Functions of Lipids

Functional lipids for instance, omega-3 and omega-6 fatty

acids, conjugated linoleic acids, medium chain triglycerides,

and phytosterols have numerous positive influences on

human health such as in obesity, blood pressure,

cardiovascular diseases, bone health, and in treating and

managing depression [7]. There is some misunderstanding

between lipids and fats, since not all lipids are fats, but all

fats are lipids. There are numerous types of lipids to discover

before completely understanding their functions, these types

include the following:

3.1. Triglycerides

Triglyceride molecules are composed of three of fatty

acids and one molecule of glycerol. The fatty acids may be

either saturated or unsaturated. Triglycerides have the ability

to float in a cell’s cytoplasm since they have a lower density

compared to water and are non-soluble, as is the case with all

lipids. A triglyceride can be categorized as a fat if it converts

to a solid at a temperature of 20°C, otherwise that are

classified as oils. They are fundamental in the body for

energy storage.

3.2. Steroids

Steroids are these organic compounds mainly composed of

four rings arranged in a specific configuration (Fig. 3). A few

categories of common steroids are cholesterol, vitamin D2,

estrogen and testosterone. These fractions of lipids have two

main biological roles: certain steroids (such as cholesterol)

are substantial constituents of cell membranes which change

the fluidity of membranes, and many steroids are signaling

molecules which stimulate steroid hormone receptors.

Fig. 3. Structure of steroids.

164 Abdelmoneim H. Ali et al.: Lipids: Functions, Applications in Food Industry and Oxidation

3.3. Phospholipids

Phospholipids can be defined as lipids containing

phosphorus. They received their name as their constitution is

primarily phosphate groups. They contain molecules that

both attract and repel water, playing a key role in the

organization of cell membranes structure. There are two

major groups of phospholipids; glycerophospholipids and

sphingolipids. Fig. 4 shows the basic structure of

phospholipids. Purified phospholipids are currently produced

commercially and have been applied in nanotechnology and

materials sciences [8].

3.4. Glycolipids

Glycolipids are lipids with a carbohydrate attached by a

glycosidic bond [9]. Short sugar chains form glycolipids,

which can be found in a cellular membrane’s exoplasmic

surface. They play an important role in enhancing the body’s

immune system, as well as helping to maintain the stability

of the membrane and attaching cells to one another to form

tissues.

Fig. 4. Structure of phospholipids.

3.5. Lipoproteins

Lipoproteins are a combination of proteins and lipids

found in a cell’s membrane – examples being enzymes and

antigens. Different types of lipoproteins are differentiated

based on specific proteins attached to the outer layer of

phospholipid, called the apolipoprotein. Lipoproteins help fat

moving around the body in the bloodstream, and exist in the

form of low density lipoprotein (HDL) and high density

lipoprotein (LDL).

3.6. Waxes

Along with a chain of alcohols, fatty acids are found in

waxes. They are chemically stable and insoluble in water and

various organic solvents. Because of these properties, waxes

are extensively distributed in both animals and plants as

protective coverings for tissues. Simple waxes are classified

as monoesters of normal fatty acids and normal long-chain

alcohols. Complex waxes as well exist, in which either the

fatty acids or alcohol components possess complex structures

in their own rights such as, vitamin esters or sterol esters

[10].

4. Applications of Lipids in Food

Industry

4.1. Role and Changes of Plant Lipids in

Processed Foods

� Plant lipids have the ability to increase the nutritional

values of foods. They also contain tocopherols and

tocotrienols, which are the major essential sources of

vitamin E.

� Lipids affect the functional properties of foods; for


example, they help to retain carbon dioxide in dough,

thus increasing the final volume of bakery products.

� The main importance of lipids is their influence on the

sensory properties. They affect the texture and increase

the viscosity of the morsel after mixing with saliva;

high viscosity is appreciated by many consumers.

� The most desirable influence of lipids is their effects on

the odor and flavor of food products. Plant lipids, being

more unsaturated than animal lipids, produce different

flavor notes as a result of culinary operations. Flavors

originating at roasting or frying temperatures are

particularly appreciated.

4.2. Frying Oils and Fats

The using of oils and fats as a frying medium in both

shallow and in deep frying mode is an important component

in the overall picture of food applications. Recently, it has

been reported that 20 million tonnes of oils and fats is used in

this way. This represents a major share of the 90 million

tonnes used for dietary purposes. Of course, it should be

taken in mind that while some of the frying oil is consumed

along with the fried foods, much is thrown away (shallow

pan frying) or ultimately finds other uses as spent frying oil.

4.3. Spreads: Butter, Ghee, Margarine

Butter. For many centuries, butter from cow’s milk fat has

been mainly used as a spread, but also for baking and frying

purposes. Butter has become less widespread with the

continuous development of good-quality margarine and other

spreads. The are some disadvantages associated with butter

such as, its comparatively high price, its poor spread-ability

(especially from the refrigerator), and its poor health profile

resulting from its high fat content, its high content of

saturated fatty acids and cholesterol, and the presence of

trans unsaturated fatty acids. Butter has the advantages of its

completely natural profile and its splendid flavor.

Ghee. Milk fat can be consumed partly as butter but also as

ghee, however the latter is declining and is now probably

below one-quarter of the combined total. Ghee is a

concentrate of butterfat with more than 99% of milk fat and

less than 0.2% moisture. It has a shelf life of 6- 8 months

even at ambient tropical temperatures. Butter or cream is

converted to ghee by controlled heating to reduce the content

of water to below 0.2%. In other procedures the aqueous

fraction is allowed to separate and some of it is run off before

residual moisture is removed by heating. Ghee is

distinguished by a cooked caramelized flavor varying slightly

with the method of preparation.

Margarine. Margarine has been produced for more than 10

decades. During the 1860 s, large sections of the European

population migrated from country to town and changed from

rural to urban occupations. At the same time, there was a

rapid increase in population in Europe and a general

recession in agriculture leading to a shortage of butter,

especially for the growing urban population. So, the price

rose beyond the reach of many poor people. So bad was the

situation in France that the government offered a prize for the

best proposal for a butter substitute that would be cheaper

and would also keep better.

The production of margarine comprises three basic steps:

emulsification of the oil and aqueous phases, crystallization

of the fat phase, and plasticification of the crystallized

emulsion. Water-in-oil emulsions are cooled in scraped-wall

heat exchangers during which time fat crystallization is

initiated, a process known as nucleation, and during which

the emulsion drop size is reduced. There follows a maturing

stage in working units during which crystallization

approaches equilibrium, though crystallization may continue

even after the product has been packed. The lipid in

margarine is part solid (fat) and part liquid (oil), and the

proportion of these two varies with temperature. The

solid/liquid ratio at different temperatures is of paramount

importance in relation to the physical nature of the product.

4.4. Baking Fats, Dough and Shortenings

The application of oils and fats in baking processes ranks

with frying and spreads as a major food use of these

materials. The products range from breads and layered dough

to cakes, biscuits (cookies) and biscuit fillings, pie crusts,

short pastry, and puff pastry. The fats used to produce this

wide range of baked goods vary in their properties and

particularly in their melting behavior and plasticity. It is

possible to achieve these properties with different blends of

oils, and preferred mixtures vary in different areas of the

world.

Fats used to make dough of various types are almost

entirely plastic fats, i.e., mixtures of solid and liquid

components that appear solid at certain temperatures and that

deform when a pressure is applied. Fats exert their effect by

interaction with the flour and (sometimes) sugar, which are

the other major constituents of a baked product.

4.5. Salad Oils and Mayonnaise

Salad oils, used in the preparation of mayonnaise and salad

cream, should be oxidatively stable and free of solids even

when stored in refrigerator. Numerous vegetable oils may be

applied. Those containing linolenic acid (soybean oil and

canola oil) are frequently lightly hydrogenated to improve the

oxidative stability. All oils are mostly winterized in order to

remove high-melting glycerides that would crystallize, as

well also waxes present in solvent-extracted oil. The latter

lead to a haze in the oil when it is been cooled. Salad oils

must pass a cold test, which needs that the oil remains clear

for 5.5 hours at the refrigeration temperature. After

appropriate treatment, soybean, canola, corn, and sunflower

oils can be used for mayonnaise production.

4.6. Incorporation of Vegetable Oils into

Dairy Products

Vegetable oils could be incorporated into dairy products as

a substitute of milk fat. This occurs when local supplies are

insufficient as in several tropical countries where the climate


is not appropriate for large-scale dairy farming and also for

consumers concerned about the saturated acids and

cholesterol existing in milk fat. Furthermore, it is possible to

produce milk fat substitutes in a more convenient form as, for

example, in long-life cream.

5. Lipids Oxidation

The mechanism of lipids oxidation is shown in Fig. 5.

Lipid oxidation or rancidity is clearly the major challenge for

stabilizing specialty oils, particularly since oils with special

nutraceutical properties have predominantly polyunsaturated

fatty acids. While there is relatively little data yet available

regarding oxidation of specialty oils per se, all oils follow the

same fundamental processes, modified by endogenous pro-

and antioxidants and innate variances in fatty acid

composition. What has been learned about lipids oxidation in

conventional food oils can be applied to predict the stability

of specialty oils and to explain the observed behaviors.

This reaction scheme is able to generate aldehydes,

ketones, alcohols and hydrocarbons. Many of the volatile

compounds produced during lipids oxidation originate

through similar dismutations.

Hydroperoxides are not stable compounds and given time,

they will break down. A typical mechanism, as presented

below, results in the formation of two radicals from a single

hydroperoxide molecule.

Both of these new radicals can initiate further oxidation,

and some metals can speed up this reaction.

Both ions and free radicals were formed, and copper was

the catalyst. Copper did not initiate the reaction, but once the

hydroperoxides were formed, it speeds up their breakdown.

Fig. 5. Mechanism of lipids oxidation

5.1. Measurements of Lipid Oxidation

5.1.1. Peroxide Value

One of the most widely used parameters for oxidative

rancidity. The detection of peroxide gives an initial indication

of rancidity in the unsaturated fats and oils [11]. Peroxides

are the basic initial products of autoxidation, they can be

measured by using procedures based on the principle of their

ability to release iodine from potassium iodide, or to oxidize

ferrous to ferric ions. Their content is frequently expressed in

terms of milliequivalents of oxygen/kg of fat. Although the

peroxide value is applicable for following peroxide formation

at the early stages of oxidation, it is, however, highly

experimental. The precision is questionable, the results vary


with details of the technique used, and the test is very

sensitive to temperature variations. Throughout the course of

oxidation, peroxide values reach a peak and then decline

[12].

5.1.2. Thiobarbituric Acid (TBA)

TBA is the most extensively used examination for

measuring the extent of lipid peroxidation in foods because

of its simplicity and because the obtained results are

extremely associated with the sensory evaluation scores. The

principle of this method depends on the reaction of one

molecule of malonaldehyde with two molecules of TBA to

generate a red malonaldehyde-TBA complex (Fig. 6), which

can be spectrophotometrically quantitated at 530 nm.

Nevertheless, this technique has been evaluated as being

nonspecific and insensitive for the detection of low

concentrations of malonaldehyde. Other TBA-reactive

substances (TBARS) including sugars and other aldehydes

could interfere with the malonaldehyde-TBA reaction. If

some of the malonaldehyde reacts with proteins in an

oxidizing system, abnormally low values may result. In many

cases, however, the TBA test is appropriate tool to compare

samples of a single material at different stages of oxidation.

Fig. 6. Proposed TBA reaction [12].

5.1.3. Iodine Value

Iodine value is used to measure the unsaturated double

bonds in fat, and is expressed in terms of percentage of the

iodine absorbed. The decline in the iodine value is

occasionally used to observe the reduction of dienoic acids

during the course of the autoxidation. The higher the iodine

number, the more double bonds are presented in the fat [13].

5.1.4. Active Oxygen Method (AOM)

This technique determines the stability of a fat by bubbling

air through a solution of the fat using specific conditions of

flow rate, temperatures, and concentration. At intervals,

peroxides and hydroperoxides resulted by this treatment are

determined by titration with iodine. The AOM value is

defined as the number of hours needed for the peroxide

concentration to reach 100 meq/kg of fat. The more stable the

fat, the longer time it will take to reach that level.

5.2. Applied Methods to Evaluate Lipids

Oxidation

The analysis and examination of lipid oxidation in

different food samples is a significant issue since the

compounds produced in the process are associated with the

undesirable sensory and biological influences. Suitable

measurement of lipid oxidation considered a challenging

mission since the process of oxidation is complicated and

depends on the category of lipid substrate, the oxidation

causes and the environmental influences. A great number of

procedures have been developed and applied so far, in order

to determine both primary and secondary products of lipids

oxidation. The most common techniques and classical

methods include, peroxide value, TBARS analysis and

chromatographic tests. Particular additional procedures such

as chemiluminescence, fluorescence emission, Raman

spectroscopy, infrared spectroscopy or magnetic resonance

deliver interesting and promising outcomes. Consequently,

consideration should be paid to these additional different

methods in the field of food lipid oxidation analysis [14].

Estimating the status of lipid oxidation is a challenging

mission because of a number of evidences such as the diverse

compounds which are produced depending on the time, the

extent of oxidation and the involved mechanism.

Consequently, selecting only one parameter to analyze the

oxidative status is rather tough and it is often more

appropriate to combine different procedures. In addition, as

indicated by Eymard, Baron [15], not only nature and

composition of lipid as the substrate of the reaction have an

influence on lipid oxidation process, but also proteins kind

and the concentration, antioxidants and prooxidants existing

in the food matrix, as well as its physicochemical properties

are parameters worthwhile to take in account. Lipid oxidation

varies depending on the source of food. For example, in meat

samples, studies suggested that the rates of lipid oxidation

may depend on the comparative ability of haemoglobins from

different animal classes to promote it [16], and also

suggested that colloidal structures designed by phospholipids

in vegetable oils could have an influence on the oxidative

stability of food oils [17]; similarly lipid oxidation was

expected to be delayed in fish sausages after the addition of

numerous antioxidants [18], and in milk samples, the role of

catechins and ascorbic acid in oxidation has been recently

studied [19]. Additionally, each method permits a number of

different experimental environments, and combined with the

lack of uniformity among laboratories, it leads to different

results that are currently unavoidable. Most of the oxidation

compounds are disposed to be moreover degraded, which

provides an added source of divergence. Therefore, accurate

control of the experimental technique should be kept.

5.2.1. Volumetric Methods

Amongst the different suggested methods for peroxides

analysis, iodometry has been the most conventional and

common technique mostly because of the simplicity of the

experimental process. Though the procedure involves prior

extraction of lipids, rapid and clear results are provided. In

acidic medium, hydroperoxides and other peroxides react

with the iodide ion to produce iodine, which is titred with a

sodium thiosulfate solution, in the existence of starch. The

AOAC provides an approved manner since 1965 [20].

According to this technique, peroxide value is considered to

represent the quantity of active oxygen (in meq) contained in

1 kg of lipid and which could oxidize the potassium iodide. It


shows, however, some drawbacks, mainly derived from the

iodide high susceptibility to oxidation in the presence of

molecular oxygen and accelerated by light exposure. As well,

spontaneous hydroperoxide formation can occur, which

would result in overestimation and absorption of iodine by

unsaturated fatty acids leading to underestimation [21].

Furthermore, it involves anhydrous systems in order to avoid

interference complications. Consequently, lipids have to be

extracted, and this procedure stage increases the contact with

oxygen. Furthermore, the peroxide value determination does

not provide actual measure of the oxidative degradation;

since peroxides are frequently further degraded; therefore

simultaneous measurement of the secondary products is

suitable.

5.2.2. VIS–UV Spectroscopic Techniques

Besides the volumetric technique, spectroscopic ones are

relatively simple and are reliable, moderately sensitive and

reproducible when they are achieved under standardized

conditions. On the other hand, they are highly experimental

in the view of the point that they measure complex mixtures

of oxidized molecules. Furthermore, they are normally work-

intensive and consume large volumes of solvents and

reagents that might be dangerous [22].

5.2.3. Ferrous Oxidation Method

The ferrous oxidation technique for the quantification of

peroxide content is easy and simple to use compared to

iodometry. The chief reason is the lower sensitivity of ferrous

ion towards the spontaneous oxidation by the oxygen existing

in the air, when compared to the high susceptibility to

oxidation of the iodide solutions. It involves the oxidation of

Fe (II) to Fe (III), mediated by hydroperoxide reduction in

acidic conditions and in the presence of either thiocyanate or

xylenol orange.

5.2.4. Iodide Oxidation Method

A spectrophotometric iodidedependant technique has

similarly been set for the determination of hydroperoxide

content. In this not so regularly applied methodology [23],

the lipid sample is placed in an acidic solution, which is then

combined with iodide. The lipid hydroperoxide oxidizes

iodide to iodine. Then, the produced iodine and iodide in

excess react to give triiodide anion, which is identified

spectrophotometrically at 350 nm. Bloomfield [24] used Fe

(II) as a catalyst in this reaction. The closed conditions

prevent interference from atmospheric oxygen, and the short

reaction time reduces the interference from side reactions.

5.2.5. Chromatographic Methods

All the methodologies described above are generally rather

simple regarding the theory base, the application of the

technique and the ulterior interpretation of the data,

presenting low-to-moderate selectivity and sensitivity,

though. In this case, chromatographic methods are far more

precise, sensible and specific for the compounds of concern,

allowing improved identification of the individual products.

In fact, their application for hydroperoxides determination

rather than that of volumetric and spectroscopic

measurements displays a growing trend over the last few

years. As an unavoidable consequence, chromatographic

approaches frequently need long or particular experimental

work, precise control of the experimental conditions and the

data processing is relatively complex [14].

Liquid chromatography. High-performance liquid

chromatography (HPLC) has been recently applied for

hydroperoxides identification. This technique is highly

sensitive and pretty multipurpose considering both column

and detector properties, allowing to identify compounds with

diverse properties of volatility, molecular weight or polarity.

However, the preparation of samples is often tedious and

regularly needs lipid extraction. Zeb and Murkovic [25]

found that the isocratic HPLC–ESI–MS was a convenient

technique for the identification and classification of oxidized

classes of triacylglycerols (TAGs), that is, mono- and bis-

hydroperoxides.

Gas chromatography. Gas chromatography coupled with

mass spectrometry (GC–MS) can also be applied for the

quantification of lipid hydroperoxides, nevertheless because

of their thermolability, previous reduction of the

hydroperoxides is required. This point, along with the

previous lipid extraction and successive derivatization step,

makes it an unwieldy and time-consuming technique [26].

5.3. Reasons for Lipids Oxidation

As shown in Fig. 7, the overall reaction mechanism of

lipid oxidation consists of three phases:

(1) Initiation, the formation of free radicals.

(2) Propagation, the free radical chain reactions.

(3) Termination, the formation of non-radical products.

The important lipids involved in oxidation are the

unsaturated fatty acid moieties, oleic, linoleic, and linolenic.

The rate of oxidation of these fatty acids increases with the

degree of unsaturation, as oleic acid has 1 times rate, linoleic

acid has 10 times and linolenic acid has 100 times.

Fig. 7. Reaction mechanism of phenolic antioxidant and hydroperoxide.

5.4. Free Radicals

Free radicals are atoms or groups of atoms with an odd

number of electrons and can be produced when oxygen

interacts with certain molecules. As soon as these highly

reactive radicals are formed, they can start a chain reaction,

like dominoes.


Types of free radicals:

The most common types of free radicals include;

superoxide (O2-), hydrogen peroxide (H2O2), hydroxyl radical

(OH-), singlet oxygen (

1O2), hydroperoxy radical (HOO

-),

lipid peroxide radical (ROO-), nitric oxide (NO

-), and

peroxynitrite, (ONOO-)

Properties of free radicals:

Highly reactive - very short half-life - generate new

radicals by chain reaction - cause damage to biomolecules,

cells and tissues in various disease conditions such as

diabetes mellitus, neurodegenerative diseases, cancer, and

cardiovascular diseases.

5.5. Analyzing the Type and Path of

Oxidation

Chemical analysis monitors the formation of primary and

secondary oxidative by-products (Fig. 8). Primary oxidative

by-product measurements are often used to determine how

close a material or matrix is to the point of failure

(oxidation). Often, only the peroxide value is used in order to

evaluate the level of lipids oxidation in different matrixes. In

fact, without secondary oxidative by-products, it is not easy

to truly judge the status of a product by only peroxide values.

Consequently, even if a product has a low peroxide value, it

does not necessarily always refer that this product is fresh.

Fig. 8. The volatiles and non-volatiles contain the secondary oxidative by products [27].

Primary oxidative by-product measurements are only one

aspect to ensure the quality of food products. In order to get a

full clear picture of where a product is on the oxidation path,

secondary oxidative by-products, such as hexanals or 2,4-

decadienals should be measured as well. These secondary by-

products are associated with the flavor components

connected to lipids oxidation. Chemical analysis gives an

insight into the timing of the oxidation pathway that sensory

analysis might not show until it is too late.

There are numerous ingredient options to choose from that

can help to control lipids oxidation, but remember when

analyzing these options, confirm the two commonly asked

questions have been answered. It is difficult to meet all

consumer requirements and expectations when delivering

quality food products that look good, taste fresh and are

consistently the same each time purchased.

5.6. Prevention of Lipids Oxidation

Lipid oxidation in foods considered a serious dilemma,

difficult to overcome often and leads to loss of shelf life,

palatability, functionality, and nutritional quality. Loss of

palatability is due to the generation of off-flavors that arise

primarily from the breakdown of unsaturated fatty acids

during autoxidation. The high reactivity of the carbon double

bonds in unsaturated fatty acids makes these substances

primary targets for free radical reactions. Autoxidation is the

oxidative deterioration of unsaturated fatty acids via an

autocatalytic process consisting of a free radical chain

mechanism.

5.7. Antioxidants

In foods containing lipids, antioxidants can delay the

beginning of oxidation or slow the rate at which it proceeds.

These substances can occur as natural components of foods,

but also they can be deliberately added to products or formed

during processing. Their role is not to enhance or improve

the quality of foods, but they do maintain food quality and

extend their shelf-life. Antioxidants used in food processing

should be distinguished by their low-cost, nontoxic,

influential at low concentrations, stable, and capable of

surviving processing (carry-through effect); color, flavor, and

odor must be negligible. The choice of the type of

antioxidant which will be used depends mostly on the

compatibility of the product and regulatory guidelines.

Antioxidants can slow lipids oxidation through

inactivating or scavenging free radicals, consequently

preventing initiation and propagation reactions. Free radical

scavengers (FRS) or chain-breaking antioxidants are able to


accept a radical from oxidizing lipids species such as peroxyl

(LOO•) and alkoxyl (LO•) radicals by the following reaction:

Antioxidants not only extend the shelf life of the product,

but also reduce raw material waste, reduce nutritional losses,

and widen the range of fats that can be used in specific

products. By extending keeping quality and increasing the

number of oils that can be used in food products, antioxidants

allow food producers to use more available and/or less costly

oils for product formulation.

5.7.1. Synthetic Antioxidants

(1) Butylated hydroxyanisole.

(2) Butylated hydroxytoluene.

(3) Tertiary butylhydroxyquinone.

(4) 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline

(Ethoxyquin).

(5) Gallates.

(6) Tocopherols.

(7) Erythorbic acid and ascorbyl palmitate.

Fig. 9. Chemical composition of synthetic antioxidants.

5.7.2. Natural Antioxidants

(1) Tocopherols and tocotrienols.

(2) Ascorbic acid and ascorbate salts.

(3) Carotenoids.

(4) Enzymatic antioxidants: glucose oxidase,

superoxide dismutase, catalase, and glutathione

peroxidase.

(5) Proteins and related substances.

(6) Maillard reaction products.

(7) Phospholipids and sterols.

(8) Sulfur dioxide and other sulfites.

6. Conclusion

Lipids have a functional and significant role in foods

because of their contribution to palatability, satiety, and

nutrition. Consequently, lipid quality is a very important

issue to consumers and may show a relation to numerous

health problems. Lipid oxidation is a major problem in many

areas of the food industry. Delaying lipid oxidation not only

prolongs the shelf-life of the products but also decreases raw

material waste, nutritional loss, and widens the range of

lipids that can be used in specific products. Therefore, by

controlling lipid oxidation, food processors can use more

available, less costly and/ more nutritionally favorable oils

for product preparations. Further studies and investigations

might be valuable in view of practical and economic

limitations on the production and effective utilization of

novel antioxidants.

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Lipids: Functions, Applications in Food Industry and Oxidation

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