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American Journal of Food Science and Nutrition Research
2016; 3(6): 162-171
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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
1
State 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
2
Department of Food Sciences, Faculty of Agriculture, Zagazig University, Zagazig, Egypt
3
Food 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
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.
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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. 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 βoxidation 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. 3. Structure of steroids.
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3.3. Phospholipids
materials sciences [8].
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
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
American Journal of Food Science and Nutrition Research 2016; 3(6): 162-171
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
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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
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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.
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.
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 proand 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.
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
American Journal of Food Science and Nutrition Research 2016; 3(6): 162-171
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
167
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
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Abdelmoneim H. Ali et al.: Lipids: Functions, Applications in Food Industry and Oxidation
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 workintensive 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 bishydroperoxides.
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.
American Journal of Food Science and Nutrition Research 2016; 3(6): 162-171
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.
169
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 2,4decadienals should be measured as well. These secondary byproducts 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
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Abdelmoneim H. Ali et al.: Lipids: Functions, Applications in Food Industry and Oxidation
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.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Natural Antioxidants
Tocopherols and tocotrienols.
Ascorbic acid and ascorbate salts.
Carotenoids.
Enzymatic
antioxidants:
glucose
oxidase,
superoxide dismutase, catalase, and glutathione
peroxidase.
Proteins and related substances.
Maillard reaction products.
Phospholipids and sterols.
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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