Download General Chemistry, Composition, Identification

Journal of Pharmaceutical Research And Opinion 1:2 (2011) 52 – 64
Contents lists available at www.innovativejournal.in
JOURNAL OF PHARMACEUTICAL RESEARCH AND OPINION
RESEARCH
Journal homepage: http://www.innovativejournal.in/index.php/jpro
General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
Mohammad Asif*
College of Pharmacy, GRD (P.G) Institute of Management & Technology, Dehradun (Uttrakhand). 248009, India.
ARTICLE INFO
ABSTRACT
Received 8 July 2011
Accepted 26 June 2011
The fats and oils obtained from natural resources, the majority of them are used
directly or just after refinement while the other are used after modification mainly
chemical means. Fats and oils are commonly called "triglycerides" resulting from the
combination of one molecule of glycerol with three molecules of fatty acids. They are
insoluble in water but soluble in most organic solvents. They have lower densities
than water. When solid appearing they are referred to as "fats" and when liquid they
are called "oils." The term "lipids" embraces a variety of chemical substances. In
addition to triglycerides, it also includes mono- and diglycerides, phosphatides,
sterols, fatty alcohols, fatty acids, fat-soluble vitamins, and other substances. The oils
and fats most frequently used for cooking oils, shortenings, margarines, food
ingredients, medicinal and other pharmaceutical uses. Fats and oils are essential
nutrients in both human and animal diets. They provide energy, essential fatty acids
(precursors for important hormones, the prostaglandins), carriers for fat soluble
vitamins, and make foods more palatable. Fats and oils are obtained from both plats
and animal sources, present in varying amounts in many foods. The principal
sources of fat in the diet are meats, dairy products, poultry, fish, nuts, and vegetable
fats and oils. Most vegetables and fruits consumed as such contain only small
amounts of fat.
Corresponding Author:
Mohammad Asif
[email protected]
Tel: +91-9897088910
College of Pharmacy, GRD
(P.G) Institute of Management
& Technology, Dehradun
(Uttrakhand). 248009, India.
KeyWords: Composition,
Fats Oil, Waxes.
INTRODUCTION
These are a large and diverse group of naturally
occurring organic compounds, esters of fatty acids and
alcohols and polyols. These are soluble in non polar organic
solvents and generally insoluble in water (1-3). These can
be classified as:
1. Simple lipids (esters of fatty acids with alcohols)
e.g. triglycerides like fats and oils, waxes.
2. Compound lipids e.g. phospholipids and
glycolipids.
They show great structural variety and can be
studied in following sections:
(a). Fatty Acids
(b). Fats and Oils
(c).Waxes
(d). Soaps and Detergents
(e). Phospholipids
a. Fatty Acids: Lipids on hydrolysis by acids or
bases yield the component fatty acid. These long-chain
carboxylic acids are generally referred by their common
names, which in most cases reflect their sources. Natural
fatty acids may be saturated or unsaturated, and the
saturated acids have higher melting points than
unsaturated acids of corresponding size.
Saturated fatty acid (stearic acid, C18:0)
Mono-unsaturated fatty acid (oleic acid, C18:1 ω9)
©2011, JPRO, All Right Reserved.
ω3)
Polyunsaturated fatty acid (linoleic acid, C18:2 ω6)
Polyunsaturated fatty acid (α-linolenic acid, C18:3
The higher melting points of the saturated fatty
acids are due to the uniform rod-like shape of their
molecules. The presence of cis-double bond in the
unsaturated fatty acids introduces a twist in their shape,
which makes it more difficult to pack their molecules
together in a stable repeating array or crystalline lattice.
The trans-double bond isomer of oleic acid, known as
elaidic acid, has a linear shape and a melting point higher
than its cis isomer. Two polyunsaturated fatty acids,
linoleic and linolenic, are designated “essential” because
their absence in the human diet has been associated with
health problems, like scaly skin, stunted growth and
increased dehydration. These acids are also precursors to
the prostaglandins, a family of physiologically potent lipids
present in minute amounts in most body tissues (4,5).
52
b. Fats and Oils: Theses are phospholipids of fatty
acids with glycerol commonly known as triglycerides,
found in both plants and animals, and compose one of the
major food groups of our diet. Triglycerides that are solid
or semisolid at room temperature are classified as fats, and
found predominantly in animals. The liquid triglycerides
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
are called as oils and originate mainly from plants;
triglycerides obtained from fish are also oils. Fats
composed of mainly saturated fatty acids while oils are
composed of unsaturated fatty acids. Saturated and transfatty acid glycerides in the diet have been associated with
atherosclerosis. Triglycerides having three identical acyl
chains, like tristearin and triolein are called as “simple”,
while those composed of different acyl chains are called
“mixed”.
c. Waxes: Waxes are esters of fatty acids with long
chain monohydric alcohols and may also contain
hydrocarbons. These are widely distributed in nature like
leaves and fruits of many plants have waxy coatings, which
protect them from dehydration. E.g. of some common
waxes are: Spermaceti wax-CH (CH ) COO-(CH ) CH ,
3
2 14
2 15
pharmacopoeias like: almond oil, castor oil, olive oil,
sesame oil, peanut oil, sunflower oil and γ-linolenic acid
containing evening primrose oil and borage oil.
CHEMICAL COMPOSITION OF FATS: Triglycerides are the
predominant component of fats and oils. The minor
components include mono- and diglycerides, free fatty
acids, phosphatides, sterols, fatty alcohols, fat-soluble
vitamins, and other substances (1-3).
Fatty acids: Triglycerides are ester of fatty acids
and glycerol. The fat or oil yield approximately 95 % of
fatty acids. Both the physical and chemical characteristics
of fats are influenced by the types and amounts of the fatty
acids and positioned on the glycerol molecule. The fatty
acids are saturated and unsaturated carbon chains with an
even number of carbon atoms and a single carboxyl group.
Edible oils also contain minor amounts of branched chain
and cyclic acids. Also odd number straight chain acids are
typically found in animal fats.
The Major Component
Triglycerides: A triglyceride is composed of
glycerol and three fatty acids. When all of the fatty acids in
a triglyceride are identical, it is termed a "simple"
triglyceride. The more common forms, however, are the
"mixed" triglycerides in which two or three kinds of fatty
acids are present in the molecule or Complex triglyceride
are the triglyceride where one or two fatty acid structures
differ from the third fatty acid.
The Minor Components
Mono and Diglycerides: Mono- and diglycerides
are mono- and diesters of fatty acids and glycerol. They are
used frequently in foods as emulsifiers. They are prepared
commercially by the reaction of glycerol and triglycerides
or by the esterification of glycerol and fatty acids. Monoand diglycerides are formed in the intestinal tract as a
result of the normal digestion of triglycerides. They also
occur naturally in very minor amounts in both animal fats
and vegetable oils.
Free Fatty Acids: Free fatty acids are the
unattached fatty acids present in a fat. Some unrefined oils
may contain several percent free fatty acids. The levels of
free fatty acids are reduced in the refining process. Refined
fats and oils have very low percent of free fatty acids.
Phosphatides: Phosphatides consist of alcohols
(usually glycerol), combined with fatty acids, phosphoric
acid, and a nitrogen-containing compound. Lecithin and
cephalin are common phosphatides found in edible fats.
Refining removes the phosphatides from the fats.
Sterols: Sterols or steroid alcohols are containing
the steroidal nucleus and 8-10 carbon side chain and an
alcohol group. Sterols are found in both animal fats and
vegetable oils with substantial biologically difference.
Cholesterol is the primary animal fat sterol and found in
vegetable oils in trace amounts. Vegetable oil sterols are
also called "phytosterols". Sitosterol and stigmasterol are
well known vegetable oil sterols. The type and amount of
vegetable oils sterols vary with the source of the oil.
Fatty Alcohols: Long chain alcohols are of little
importance in most edible fats. A small amount esterified
with fatty acids is present in waxes found in some
vegetable oils. Larger quantities are found in some marine
oils.
Vitamins: Generally, most fats and oils are not
good sources of vitamins other than vitamin E. The fatsoluble vitamins A and D sometimes are added to foods
3
Beeswax-CH (CH ) COO-(CH ) CH and Carnuaba wax3
2 24
CH (CH ) CO -(CH ) CH .
3
2 30
2
2 33
3
2 29
3
d. Soaps and Detergents: Carboxylic acids and
salts having alkyl chains longer than eight carbons exhibit
unusual behavior in water due to the presence of both
-
hydrophilic (COO ) and hydrophobic (alkyl) regions in the
same molecule. Such molecules are known as amphiphilic
or amphipathic. Fatty acids made up of ten or more carbon
atoms are nearly insoluble in water, and float on the
surface when mixed with water because of their lower
density. These fatty acids spread evenly over water surface
and form a monomolecular layer in which the polar
carboxyl groups are hydrogen bonded at the water
interface, and the hydrocarbon chains are aligned together
away from water surface. These substances accumulate at
water surface and change the surface properties called as
surfactants. Alkali metal salts of fatty acids are more
soluble in water than the acids themselves, and the
amphiphilic character of these substances also make them
strong surfactants. The most common examples of such
compounds are soaps and detergents, each of these
molecules has a nonpolar hydrocarbon chain, the “tail”, and
a polar (ionic) “head group”. The use of such compounds as
cleaning agents is facilitated by their surfactant character,
which lowers the surface tension of water, allowing it to
penetrate and wet a variety of materials.
e. Phospholipids: These are main constituents of
cell membranes; resemble the triglycerides in being ester
or amide derivatives of glycerol or sphingosine with fatty
acids and phosphoric acid. The phosphate moiety of the
resulting phosphatidic acid is further esterified with
ethanolamine, choline or serine in the phospholipids itself.
The fatty acid components may be saturated or
unsaturated. Liposomes are microscopic vesicles consisting
of an aqueous core enclosed in one or more phospholipids
layers. They are formed when phospholipids are vigorously
mixed with water. The bilayer membrane that separates
the interior of a cell from the surrounding fluids is largely
composed of phospholipids, but it incorporates many other
components, such as cholesterol, that contribute to its
structural integrity. Protein channels that permit the
transport of various kinds of chemical species in and out of
the cell are also important components of cell membranes.
The sphingomyelins are also membrane lipids. They are the
major component of the myelin sheath surrounding nerve
fibers. Multiple Sclerosis is a devastating disease in which
the myelin sheath is lost, causing paralysis Several
vegetable oils have been included in different
53
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
Conjugated fatty acids: Polyunsaturated fatty
acids exhibiting pairs of unsaturated carbons not separated
by at least one saturated carbon.
which contain fat because they serve as good carriers and
are widely consumed.
Tocopherols: Tocopherols are important minor
constituents of most vegetable fats. They are antioxidants
to retard rancidity and as sources of the essential nutrient
vitamin E. There are four types of tocopherols, among
tocopherols; alpha-tocopherol has the highest vitamin E
activity and the lowest antioxidant activity. Tocopherols
may be partially removed by processing. They are not
present in appreciable amounts in animal fats. These or
other antioxidants may be added after processing to
improve oxidative stability in finished edible oils and fats.
Carotenoids and Chlorophyll: Carotenoids are
color materials occurring naturally in fats and oils. Most
range in color from yellow to deep red. Chlorophyll is the
green coloring matter of plants. The naturally occurring
level of chlorophyll in oils may be sufficient for the oils to
be tinged green. The levels of these color bodies are
reduced during the normal processing of oils to give them
acceptable color, flavor, and stability.
CLASSIFICATION OF FATTY ACIDS
Fatty acids are classified according to their degree
of saturation (Table 1). In the International Union of Pure
and Applied Chemistry (IUPAC) system of nomenclature,
the carbons in a fatty acid chain are numbered
consecutively from the end of the chain, the carbon of the
carboxyl group being considered as number 1. By
convention, a specific bond in a chain is identified by the
lower number of the two carbons that it joins.
Saturated Fatty Acids: Those containing only
single carbon-to-carbon bonds are termed "saturated" and
are the least reactive chemically. The melting point of
saturated fatty acids increases with chain length. The
longer chain fatty acids are solids at room temperatures
(Table 2).
Unsaturated Fatty Acids: Fatty acids containing
one or more carbon-to-carbon double bonds are termed
"unsaturated." Oleic acid (cis-9-octadecenoic acid) is the
fatty acid that occurs most frequently in nature. When the
fatty acid contains one double bond it is called
"monounsaturated." If it contains more than one double
bond, it is called "polyunsaturated." When two fatty acids
are identical except for the position of the double bond,
they are referred to as positional isomers. The presence of
double bonds, unsaturated fatty acids are more reactive
chemically than are saturated fatty acids. This reactivity
increases as the number of double bonds increases.
Although double bonds normally occur in a non-conjugated
position, they can occur in a conjugated position. With the
bonds in a conjugated position, there is a further increase
in certain types of chemical reactivity like oxidation and
polymerization (Table 3).
Polyunsaturated Fatty Acid: The polyunsaturated
fatty
acids,
linoleic,
linolenic,
arachidonic,
eicosapentaenoic, and docosahexaenoic acids containing
respectively two, three, four, five, and six double bonds.
Vegetable oils are the principal sources of linoleic and
linolenic acids (Table 3). Arachidonic acid is found in small
amounts in lard, which also contains about 10% of linoleic
acid. Fish oils contain large quantities of a variety of longer
chain fatty acids having three or more double bonds
including eicosapentaenoic and docosahexaenoic acids
(6,7).
ISOMERISM OF UNSATURATED FATTY ACIDS
Isomers are two or more substances composed of
the same elements combined in the same proportions but
differing in molecular structure. The two important types
of isomerism among fatty acids are geometric and
positional.
Geometric Isomerism: Unsaturated fatty acids can
exist in either the cis or trans form depending on the
configuration of the hydrogen atoms attached to the carbon
atoms joined by the double bonds. If the hydrogen atoms
are on the same side of the carbon chain, the arrangement
is called cis. If the hydrogen atoms are on opposite sides of
the carbon chain, the arrangement is called trans.
Conversion of cis isomers to corresponding trans isomers
result in an increase in melting points (Figure 1).
Fig 1 Geometrical isomerism of unsaturated fatty acids
A comparison of cis and trans molecular
arrangements, all double bonds are in the cis configuration
except for elaidic acid and vaccenic acid which are trans.
Elaidic and oleic acids are geometric isomers; in the former,
the double bond is in the trans configuration and in the
latter, in the cis configuration. Generally speaking, cis
isomers are those naturally occurring in food fats and oils.
Trans isomers occur naturally in ruminant animals such as
cows, sheep and goats and also result from the partial
hydrogenation of fats and oils.
Positional Isomerism: In this case, the location of
the double bond differs among the isomers. Petroselinic
acid, which is present in parsleyseed oil, is cis-6octadecenoic acid and a positional isomer of oleic acid, cis9-octadecenoic acid. Vaccenic acid, which is a minor acid in
tallow and butterfat, is trans-11-octadecenoic acid and is
both a positional and geometric isomer of oleic acid. The
position of the double bonds affects the melting point of the
fatty acid to a limited extent. Shifts in the location of double
bonds in the fatty acid chains as well as cis-trans
isomerization may occur during hydrogenation. The
number of positional and geometric isomers increases with
the number of double bonds. For example, with two double
bonds, the following four geometric isomers are possible:
cis-cis, cis-trans, trans-cis, and trans-trans. Trans-trans
dienes, however, are present in only trace amounts in
partially hydrogenated fats and thus are insignificant in the
human food supply (8-11).
Nomenclature of fatty acids
The systemic nomenclature of fatty acids is
derived from the name of its parent hydrocarbon by
replacing its final e by oleic acid. Thus the names of
saturated fatty acids end with the suffix anoic acid and
those of unsaturated fatty acids with the suffix enoic acid.
The numbering of carbon atoms in fatty acids is started at
the carboxyl terminus and end methyl carbon is known as
omega carbon atom. (Figure 2)
Fig 2 Numbering of carbon atoms in fatty acids
54
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
Various conventions are
adopted for indicating the position
of the double bonds. The most
widely used are involve the use of
the symbol Δ fallowed by
superscript number. For example
Δ9 means that there is a double
bound between carbon 9 and
carbon 10. Alternatively the
position of the double bond is
indicated by the numerals as in
case simple alkenes. Lastly note
that total number of carbon atoms
and number of position(s) of
double bond(s) is again indicated
Table 2 Common Saturated fatty acids
Systematic
Common No. of
Name
Name
Carbon
Atoms*
Ethanoic
Acetic
2
Butanoic
Butyric
4
Hexanoic
Caproic
6
Octanoic
Caprylic
8
Decanoic
Capric
10
Dodecanoic
Lauric
12
Tetradecanoic Myristic
14
by convention. Examples, the symbol 18;0 denote a C18 fatty acid with no double
bonds, the symbol 18: 1; 9 denote a C 18 fatty acid with a double bond between
carbon 9 and carbon 10 and the symbol 18: 2; 9,12 denote a C 18 fatty acid with
two double bonds between C9 and C10 and between C12 and 13. (12)
Table 1 Some common saturated and saturated fatty acids
Saturated
Mol. formula
Unsaturated Molecular formula
Lauric acid
CH (CH ) CO H Arachidonic CH (CH ) (CH=CHCH ) (CH ) CO H
3
2 10
2
3
2 4
2 4
2 2
2
acid
Myristic acid CH (CH ) CO H Palmitoleic CH (CH ) CH=CH(CH ) CO H
3
2 12
2
3
2 5
2 7
2
acid
Palmitic acid CH (CH ) CO H Oleic acid
CH (CH ) CH=CH(CH ) CO H
Stearic acid
3
2 14
2
3
2 16
2
Arachidic acid CH (CH ) CO H Linolenic
3
2 18
2
acid
M.P.ᵒC
3
2 7
2 7
2
CH (CH ) CO H Linoleic acid CH (CH ) CH=CHCH CH=CH(CH ) CO H
Typical Fat
Source
--7.9
-3.4
16.7
31.6
44.2
54.4
-Butterfat
Butterfat
Coconut oil
Coconut oil
Coconut oil
Butterfat,
coconut oil
Hexadecanoic Palmitic
16
62.9
Most fats and
oils
Octadecanoic Stearic
18
69.6
Most fats and
oils
Eicosanoic
Arachidic 20
75.4
Peanut oil
Docosanoic
Behenic
22
80.0
Peanut oil
*A number of saturated odd and even chain acids are present in
trace quantities in many fats and oils.
ESSENTIAL FATTY ACIDS
Certain long chain polyunsaturated fatty acids, linoleic and
arachidonic, are essential for nutrition and growth. These
linoleic and linolenic acids are "essential" because they
cannot be synthesized by the body and must be supplied in
the diet. Arachidonic acid, can be synthesized by the body
from dietary linoleic acid and is consider as an essential
fatty acid because it is an essential component of
membranes and a precursor of a group of hormone-like
compounds called eicosanoids including prostaglandins,
thromboxanes, and prostacyclins. These are important in
the regulation of various physiological processes. Linolenic
acid is also a precursor of a special group of prostaglandins.
These essential fatty acids must have a particular chemical
structure, namely, double bonds in the cis configuration
and in specific positions (carbons 9 and 12 or 9, 12, and 15
from the carboxyl carbon atom or carbons 6 and 9 or 3, 6
3
2 4
2
2 7
2
CH CH CH=CHCH CH=CHCH CH=CH(CH ) CO
3
2
2
2
2 7
Table 3 Some Unsaturated Fatty Acids in Food Fats and Oils
Systematic Common No. of No. of M.P Typical Fat
Name Name
Double Carbon ᵒC
Source
Bonds Atoms
9-Decenoic
Caproleic 1
10
Butterfat
9-Dodecenoic Lauroleic 1
12
Butterfat
9-Tetradeceno Myristolei 1
14
18.5 Butterfat
9-Hexadeceno Palmitoleic 1
16
Some fish oils,
beef fat
9-Octa
Oleic
1
18
16.3 Most fats and o
decenoic
9-Octa
Elaidic
1
18
43.7 Partially
decenoic*
Hydrogenated
oils
11-Octa
Vaccenic
1 18
44
Butterfat
decenoic*
9,12-Octa
Linoleic
2 18
-6.5 Most vegetable
decadienoic
oils
9,12,15Linolenic
3 18
-12.8 Soybean oil,
Octadecatrien
canola oil
9-Eicosenoic Gadoleic
1 20
Some fish oils
5,8,11,14Arachidon
4 20
-49.5 Lard
Eicosatetraeno
5,8,11,14,17- 5 20
Some fish oils
Eicosa
pentaenoic
13-Docosenoi Erucic
1 22
33.4 Rapeseed oil
4,7,10,13,16,
6 22
Some fish oils
19-Docosa
hexaenoic
*All double bonds are in the cis configuration except for elaidic acid
and vaccenic acid which are trans
55
and 9 from the methyl end of the molecule) on the carbon
chain (13,14).
FACTORS AFFECTING PHYSICAL CHARACTERISTICS OF
FATS AND OILS:
The physical characteristics of a fat or oil are dependent
upon the degree of unsaturation, the length of the carbon
chains, the isomeric forms of the fatty acids, molecular
configuration, and the type and extent of processing (12,
15-18).
Degree of unsaturation of Fatty Acids: Fats and oils are
made up of triglyceride molecules which may contain both
saturated and unsaturated fatty acids. Depending on the
type of fatty acids, triglycerides can be classified as mono,
di, tri and polyunsaturated. Generally, fats that are liquid at
room temperature tend to be more unsaturated than solid
or fats. It is not always true that all fats which are liquid at
room temperature are high in unsaturated fatty acids. For
2
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
example, coconut oil has a high level of saturates, but many
are of low molecular weight, hence this oil melts at or near
room temperature. Thus, the physical state of the fat does
not necessarily indicate the amount of unsaturation. The
degree of unsaturation or number of double bonds present
in fats or oils, normally is expressed in terms of the iodine
value of fats/oils.
Length of Carbon Chains in Fatty Acids: As the chain
length of the saturated fatty acid increases, the melting
point also increases. Thus, a short chain saturated fatty acid
such as butyric acid has a lower melting point than
saturated fatty acids with longer chains. Some of the higher
molecular weight unsaturated fatty acids, such as oleic acid
also have relatively low melting points. The melting
properties of triglycerides are related to those of their fatty
acids. This explains why coconut oil, which contains almost
90% saturated fatty acids but with a high proportion of
relatively short chain low melting fatty acids, is a clear
liquid at room temperature in contrast to lard which
contains only about 37% saturates, most with longer
chains, is semi-solid at room temperature.
Molecular Configuration of Triglycerides: The molecular
configuration of triglycerides can also affect the properties
of a fat or oil. Melting points (M.P) of fats will depend on
the number of different chemical entities which are
present. A simple triglyceride will have a sharp M.P. A
mixture of triglycerides, as most vegetable shortenings, will
have a broad melting range. A mixture of several
triglycerides has a lower M.P. than would be predicted for
the mixture based on the M.P. of the individual
components. The mixture will also have a broader melting
range than any of its components. Monoglycerides and
diglycerides have higher melting points than triglycerides
with a similar fatty acid composition.
Isomeric Forms of Fatty Acids: The saturated fatty acids
will have higher melting points than those that are
unsaturated. The melting points of unsaturated fatty acids
are profoundly affected by position and conformation of
the double bonds. For example, the monounsaturated fatty
acid oleic acid and its geometric isomer elaidic acid have
different melting points. Oleic acid is liquid at temperatures
considerably below room temperature, whereas elaidic
acid is solid even at temperatures above room
temperature. It is the presence of isomeric fatty acids in
many vegetable shortenings and margarines that
contributes substantially to the semi-solid form of these
products. Thus, the presence of different geometric isomers
of fatty acids influences the physical characteristics of the
fat.
Polymorphism of Fats: Solidified fats exhibit
polymorphism, i.e., they can exist in several different
crystalline forms, depending on the manner in which the
molecules orient themselves in the solid state. The crystal
forms of fats can transform from lower melting to
successively higher melting modifications. The rate of
transformation and the extent to which it proceeds are
governed by the molecular composition and configuration
of the fat, crystallization conditions, and the temperature
and duration of storage. Mechanical and thermal agitation
during processing and storage at elevated temperatures
tend to accelerate the rate of crystal transformation. The
crystal form of the fat has a marked effect on the M.P. and
the performance of the fat in the various applications in
which it is utilized. In order to obtain desired product
plasticity, functionality, and stability, the shortening or
margarine must be in a crystalline form called "beta-prime"
(a lower melting polymorph).
56
PROCESSING FOR QUALITY IMPROVEMENTS
General: Food fats and oils are derived from oilseed and
animal sources. Animal fats are generally heat rendered
from animal tissues to separate them from protein and
other naturally occurring materials. Rendering may be
either with dry heat or with steam. Vegetable fats are
obtained by the extraction or the expression of the oil from
the oilseed source. Historically, cold or hot expression
methods were used. These methods have been replaced
with solvent extraction or pre-press/solvent extraction
methods which give a better oil yield. In this process the oil
is extracted from the oilseed by hexane (a light petroleum
fraction) and the hexane is then separated from the oil,
recovered, and reused. Because of its high volatility, no
hexane residue remains in the finished oil after processing.
The fats and oils obtained directly from rendering or from
the extraction of the oilseeds are termed "crude" fats and
oils. Crude fats and oils contain varying but relatively small
amounts of naturally occurring non-glyceride materials
that are removed through a series of processing steps. For
example, it may contain small amounts of protein, free fatty
acids, and phosphatides which must be removed through
subsequent processing to produce the desired shortening
and oil products. Similarly, meat fats may contain some free
fatty acids, water, and protein which must be removed. It
should be pointed out, however, that not all of the
nonglyceride materials are undesirable elements.
Tocopherols, for example, perform the important function
of protecting the oils from oxidation and provide vitamin E.
Partial hydrogenation is employed frequently to improve
the stability of fats and oils and to provide increased
usefulness by imparting a semi-solid consistency to the fat
for many food applications. The modern processing of
edible fats and oils is the single factor most responsible for
upgrading the quality of the fats and oils consumed in the
diet today (19-22).
Degumming: Crude oils having relatively high levels of
phosphatides (e.g., soybean oil) may be degummed prior to
refining to remove the majority of those phospholipid
compounds. The process generally involves treating the
crude oil with a limited amount of water to hydrate the
phosphatides and make them separable by centrifugation.
Phospholipids are often recovered and further processed to
yield a variety of lecithin products.
Refining: The process of refining ("alkali refining")
generally is performed on vegetable oils to reduce the free
fatty acid content and to remove other gross impurities
such as phosphatides, proteinaceous, and mucilaginous
substances. The most important method of refining is the
treatment of the fat or oil with an alkali solution. This
results in a large reduction of free fatty acids by conversion
into water-soluble soaps. Most phosphatides and
mucilaginous substances are soluble in the oil only in an
anhydrous form and upon hydration with the caustic or
other refining solution are readily separated. After alkali
refining, the fat or oil is water-washed to remove residual
soap.
Bleaching: The term "bleaching" refers to the process for
removing color producing substances and for further
purifying the fat or oil. Normally, bleaching is accomplished
after the oil has been refined. The usual method of
bleaching is by adsorption of the color producing
substances on an adsorbent material. Acid-activated
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
distinguished from cocoa butter by their content of trans
acids. This process results higher solid fat content and
longer shelf life without rancidity in fat-containing
products (23-29).
Partially hydrogenated: The term used to describe an oil
which has been lightly to moderately hydrogenated to shift
the melting point to a higher temperature range and
increase the stability of the oil. The carbon-hydrogen makeup of a fatty acid describing a shortage of hydrogen atoms
in the molecule. Partially hydrogenated oils remain liquid
and are used in a wide variety of food applications.
A typical example of hydrogenation is in the process of
margarine and shortening production. Vegetable oil is
hydrogenated with gaseous H 2 in the presence of a metal
catalyst (usually nickel). If the hydrogenation is completely
performed, all the double bounds are converted to the
saturated ones with the same carbon number. For example,
complete hydrogenation of linoleic acid generates stearic
acid. Margarine and shortening makers “partially
hydrogenate” their product. They only add hydrogen atoms
until the oil is at the desired consistency. When they stop
the incomplete hydrogenation process, unsaturated fatty
acids are in varying stages of hydrogenation. Some
molecules are mostly hydrogenated, while others are not.
And the double bonds have often shifted to unnatural
positions, resulting in the generation of trans fatty acids or
trans fat, which is thought to increase risk of coronary
heart disease.
The hydrogenation process is easily controlled and can be
stopped at any desired point. As hydrogenation progresses,
there is generally a gradual increase in the melting point of
the fat or oil. If the hydrogenation of cottonseed or soybean
oil, for example, is stopped after only a small amount of
hydrogenation has taken place, the oils remain liquid.
These partially hydrogenated oils are typically used to
produce institutional cooking oils, liquid shortenings and
liquid margarines. This conversion also affects trans fatty
acids eliminating them from fully hydrogenated fats. If an
oil is hydrogenated completely, the carbon to carbon
double bonds are eliminated completely and the resulting
product is a hard brittle solid at room temperature. The
hydrogenation conditions can be varied by the
manufacturer to meet certain physical and chemical
characteristics desired in the finished product. This is
achieved through selection of the proper temperature,
pressure, time, catalyst, and starting oils. Both positional
and geometric (trans) isomers are formed to some extent
during hydrogenation, the amounts depending on the
conditions employed.
Esterification: For the most part, fatty acids are present in
nature in the form of esters and are consumed as such.
Triglycerides, the predominant constituents of fats and oils,
are examples of esters. When consumed and digested, fats
are hydrolyzed initially to diglycerides and monoglycerides
which are also esters. Carried to completion, these esters
are hydrolyzed to glycerol and fatty acids. In the reverse
process, esterification, an alcohol such as glycerol is
reacted with an acid such as a fatty acid to form an ester
such as mono-, di-, and triglycerides. In an alternative
esterification process, called alcoholysis, an alcohol such as
glycerol is reacted with fat or oil to produce esters such as
mono- and diglycerides. Using the foregoing esterification
processes, edible acids, fats, and oils can be reacted with
edible alcohols to produce useful food ingredients that
bleaching earth or clay, sometimes called bentonite, is the
adsorbent material that has been used most extensively.
This substance consists primarily of hydrated aluminum
silicate. Anhydrous silica gel and activated carbon also are
used as bleaching adsorbents to a limited extent.
Deodorization: Deodorization is a vacuum steam
distillation process for the purpose of removing trace
constituents that give rise to undesirable flavors, colors and
odors in fats and oils. Normally this process is
accomplished after refining and bleaching. The
deodorization of fats and oils is simply a removal of the
relatively volatile components from the fat or oil using
steam. This is feasible because of the great differences in
volatility between the substances that give flavors, colors
and odors to fats and oils and the triglycerides.
Deodorization is carried out under vacuum to facilitate the
removal of the volatile substances, to avoid undue
hydrolysis of the fat, and to make the most efficient use of
the steam. Deodorization does not have any significant
effect upon the fatty acid composition of most fats or oils.
In the case of vegetable oils, sufficient tocopherols remain
in the finished oils after deodorization to provide stability.
Fractionation (Including Winterization): Fractionation
is the removal of solids by controlled crystallization and
separation techniques involving the use of solvents or dry
processing. Dry fractionation encompasses both
winterization and pressing techniques and is the most
widely practiced form of fractionation. It relies upon the
differences in melting points and triglyceride solubility to
separate the oil fractions. Winterization is a process
whereby material is crystallized and removed from the oil
by filtration to avoid clouding of the liquid fraction at
cooler temperatures. The term winterization was originally
applied decades ago when cottonseed oil was subjected to
winter temperatures to accomplish this process.
Winterization processes using temperature to control
crystallization are continued today on several oils. A similar
process called dewaxing is utilized to clarify oils containing
trace amounts of clouding constituents. Pressing is a
fractionation process sometimes used to separate liquid
oils from solid fat. This process presses the liquid oil from
the solid fraction by hydraulic pressure or vacuum
filtration. This process is used commercially to produce
hard butters and specialty fats from oils such as palm and
palm kernel. Solvent fractionation is the term used to
describe a process for the crystallization of a desired
fraction from a mixture of triglycerides dissolved in a
suitable solvent. Fractions may be selectively crystallized at
different temperatures after which the fractions are
separated and the solvent removed. Solvent fractionation is
practiced commercially to produce hard butters, specialty
oils, and some salad oils from a wide array of edible oils.
CHEMICAL MODIFICATION OF OILS AND FATS
Hydrogenation: Hydrogenation is carried out to remove
the unsaturation of fatty acids and hence to increase the
oxidative stability and melting point of oils. Depending on
the extent of hydrogenation, the oils and fats can be
modified to products of various hardnesses, thus giving a
wider range of utilisation. Controlled hydrogenation of oil
with a M.P of about 27-28°C produces a useful range of
hydrogenated (hardened) fats with melting points of 3241°C. High-trans-type fats can be produced by selectively
hydrogenating fats, or by a combination of selective
hydrogenation and fractionation from liquid oils such as
soyabean oil or blends of oils. These fats are easily
57
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
include many of the emulsifiers listed in the following
section (30,31).
Interesterification: A process used by oil processors
permits a rearrangement or a redistribution of the fatty
acids on the glycerol fragment of the molecule. This
process, referred to as interesterification, is accomplished
by catalytic methods at relatively low temperature. Under
some conditions the fatty acids are distributed in a more
random manner than they were present originally (Figure
3). Other conditions permit the rearrangement process to
direct the fatty acid distribution to an extent that allows
further modification of shortening properties to be
obtained. The rearrangement process does not change the
degree of unsaturation or the isomeric state of the fatty
acids as they transfer in their entirety from one position to
another. Lard in its natural state possesses a very narrow
temperature range over which it has good consistency for
practical use in the kitchen. At slightly above normal room
temperature, ordinary lard becomes somewhat softer than
desirable, and at temperatures slightly lower, it becomes
somewhat firmer than is desirable. Molecularly rearranged
lard shortenings have a satisfactory consistency over a
much wider temperature range. The commercial
application for interesterification is the production of
specialty fats for the confectionery and vegetable dairy
industries. This process permits further tailoring of
triglyceride properties to achieve the required steep
melting curves. Treating oils and fats with sodium
methoxide as a catalyst at 80 °C causes intermolecule ester
exchange, changing the molecular composition, while
leaving the fatty acid composition unchanged. As a result,
the oil changes its physical properties such as melting point
and consistency. Natural lard tends to form a rough crystal,
which is difficult to handle, during storage. This is because
64% of palmitic acid is attached to 2nd position of
triacylglycerol molecules. Randomizing the positional
distribution of fatty acids of natural lard by
interesterification improves its physical property, making it
a smooth “rearranged lard”. Another example of
interesterification is in the field of margarine production.
Interesterification of soybean oil and completely
hydrogenated soybean oil provides a material for
margarine. This rearranged oil has an advantage that it
does not contain trans fatty acid, because it is not made
through partial hydrogenation (30-34).
more of the ingredients or added separately, provide
emulsion stability. Lack of stability results in separation of
the oil and water phases. Some emulsifiers also provide
valuable functional attributes in addition to emulsification.
These include aeration, starch and protein complexing,
hydration, crystal modification, solubilization, and
dispersion (Table 5).
Additive Effect Provided: Tocopherols, Butylated
hydroxyanisole (BHA), Butylated hydroxytoluene (BHT),
Tertiary butylhydroquinone (TBHQ), Antioxidant, retards
oxidative rancidity, Carotene (pro-vitamin A) Color
additive, enhances color of finished foods, Methyl silicone
(dimethylpolysiloxane) (Table 6). Inhibits oxidation
tendency and foaming of fats and oils during frying.
Diacetyl Provides buttery odor and flavor to fats and oils.
Lecithin Water scavenger to prevent lipolytic rancidity,
Citric acid, Phosphoric acid, Metal chelating agents, inhibit
metal-catalyzed, oxidative breakdown.
Alkaline Hydrolysis: Alkaline hydrolysis (saponification)
of oil to make soaps. There are many methods for
hydrolysis of triacylglycerol molecule. The most common
method is alkaline hydrolysis. Heating (around 100°C)
triacylglycerols with aqueous solution of sodium hydroxide
results in glycerol and alkaline salt of fatty acid (i.e. soap).
This is called saponification, and used for production of
soap.
Transesterification: Transesterificaton includes chemical
reactions where an ester is reacted with alcohol
(alcoholysis), acid (acidolysis), or another ester
(intereseterification or ester exchange), to generate a new
ester.
Alcoholysis: Methanolysis of oil for the production of fatty
acid methylester. When methanol is used in alcoholysis, the
reaction is called methanolysis, in which fatty acid methyl
ester and glycerol are generated. Fatty acid methyl esters
can be used as an alternative fuel for diesel engine
(biodiesel). Biodiesel is a substitute or extender for
traditional petroleum diesel. It can be used in conventional
diesel engines, and the use of biodiesel is advantageous for
reducing emission of CO 2 , CO, SO 2 and particle materials.
Biodiesel is now spreading worldwide. For example, in
France, all the diesel fuel marketed contains 5% of
biodiesel. Another example of alcoholysis is glycerolysis,
where triacylglycerol is reacted with glycerol (alcohol) in
the presence of alkaline catalyst to form partial glyceride
such as onoacylglycerol. A mixture of triacylglycerol and
glycerol are heated at 200-250°C in the presence of sodium
hydroxide. The resulting main product is monoacylglycerol,
which is used as food emulsifier after purification by
molecular distillation. Glycerolysis. In practical process, the
product is a mixture of mono- and diacylglycerols.
Acidolysis: An industrial application of acidolysis is
production of long chain fatty acid vinyl esters from vinyl
acetate (this is obtained by chemical reaction of ethylene
and acetic acid) and fatty Production of fatty acid vinyl
ester by acidolysis. acids. Long chain fatty acid vinyl esters
are industrial raw material for making plastics.
Fig 3 Interesterification within triglycerides
SOME DIRECT FOOD ADDITIVES USED IN FATS AND
OILS
Additives and Processing Aids: Manufacturers may add
low levels of approved food additives to fats and oils to
protect their quality in processing, storage, handling, and
transporting of finished products (35-41). This insures
quality maintenance from time of production to time of
consumption (Table 4).
Emulsifiers: Many foods are processed and/or consumed
as emulsions, which are dispersions of immiscible liquids
such as water and oil, e.g., milk, ice cream, icings, and
sausage. Emulsifiers, either present naturally in one or
58
REACTIONS OF FATS AND OILS
Hydrolysis: Glycerides can be hydrolyzed readily like
other esters. Partial hydrolysis of triglycerides will yield
mono and diglycerides and fatty acids. When the hydrolysis
is carried to completion with water in the presence of an
acid catalyst, the mono-, di-, and triglycerides will
hydrolyze to yield glycerol and fatty acids. With aqueous
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
sodium hydroxide, glycerol and the sodium salts of the
component fatty acids (soaps) are obtained. In the digestive
tracts of humans and animals and in bacteria, fats are
hydrolyzed by enzymes (lipases). Lypolytic enzymes are
present in some edible oil sources (palm, coconut). Any
residues of these lipolytic enzymes present in some crude
fats and oils are deactivated by the temperatures used in oil
processing, so enzymatic hydrolysis is unlikely in refined
fats and oils. The chemical reaction of fats with water to
form glycerol and free fatty acids.
Table 4 Some processing aids used in manufacturing edible fats and Oils
Aid
Effect
Sodium hydroxide
Refining aid
Carbon/clay
Bleaching aid
Nickel
Hydrogenation catalyst
Sodium methoxide
Rearrangement catalyst Water or acid, neutralization, filtration,
and deodorization
Phosphoric acid, Citric acid
Refining acids, metal Chelators
Acetone, Hexane, Isopropanol
Nitrogen
Polyglycerol esters
Silica hydrogel
Sodium lauryl sulfate
Crystallization media for fractionation of fats and oils
Oxygen replacement
Crystallization modification
Adsorbent
Fractionation aid, wetting Agent
Mode of Removal
Acid neutralization
Filtration
Filtration
filtration,
and deodorization
Neutralization with base,
filtration, or water washing
Solvent stripping and
Deodorization
Diffusion
None
Filtration
Washing and centrifugation
Table 5 Emulsifiers and Their Functional Characteristics inand odors characteristic of the condition known as
Processed Foods
"oxidative rancidity." Some fats resist this change to a
Emulsifier
Mono-diglycerides
Characteristic
Emulsification of water in oil,
Anti-staling or softening,
Prevention of oil separation
Lecithin
Viscosity control and wetting,
Antispattering and antisticking
Lactylated mono-diglycerides Aeration Gloss enhancement
Polyglycerol esters
Crystallization promoter, Aerati
Emulsification
Sucrose fatty acid esters
Emulsification
Sodium steroyl lactylate (SSL), Aeration, dough conditioner,
Calcium steroyl lactylate (CSL) Stabilizer
Table 6 Some Direct Food Additives used in Fats and Oils
Additive Effect Provided
Tocopherols, Butylated
hydroxyanisole (BHA), Butylate
hydroxytoluene (BHT), Tertiary
butylhydroquinone (TBHQ)
Carotene (pro-vitamin A)
Methyl silicone
(dimethylpolysiloxane)
Diacetyl
Lecithin
Citric acid Phosphoric acid
Effect Provided
Antioxidant, retards oxidative
rancidity
Color additive, enhances color of
finished foods
Inhibits oxidation tendency and
foaming of fats and oils during
frying
Provides buttery odor and flavor
fats and oils
Water scavenger to prevent
lipolytic rancidity
Metal chelating agents, inhibit
metal-catalyzed oxidative
breakdown
OXIDATION OF FATS
Autoxidation: Of particular interest in the food field is the
process of oxidation induced by air at room temperature
referred to as "autoxidation." Ordinarily, this is a slow
process which occurs only to a limited degree. In
autoxidation, oxygen reacts with unsaturated fatty acids.
Initially, peroxides are formed which in turn break down to
hydrocarbons, ketones, aldehydes, and smaller amounts of
epoxides and alcohols. Heavy metals present at low levels
in fats and oils can promote autoxidation. Fats and oils
often are treated with chelating agents such as citric acid to
inactivate heavy metals. The result of the autoxidation of
fats and oils is the development of objectionable flavors
59
remarkable extent while others are more susceptible
depending on the degree of unsaturation, the presence of
antioxidants, and other factors. The presence of light, for
example, increases the rate of oxidation. It is a common
practice in the industry to protect fats and oils from
oxidation to preserve their acceptable flavor and shelf life.
When rancidity has progressed significantly, it is apparent
from the flavor and odor of the oil. Expert tasters are able
to detect the development of rancidity in its early stages.
The peroxide value determination, if used judiciously, may
be helpful in measuring the degree of oxidative rancidity in
the fat. It has been found that oxidatively abused fats can
complicate nutritional and biochemical studies in animals
because they can affect food consumption under ad libitum
feeding conditions and reduce the vitamin content of the
food. If the diet has become unpalatable due to excessive
oxidation of the fat component and is not accepted by the
animal, a lack of growth by the animal could be due to its
unwillingness to consume the diet. Thus, the experimental
results might be attributed unwittingly to the type of fat or
other nutrient being studied rather than to the condition of
the ration. Knowing the oxidative condition of unsaturated
fats is extremely important in biochemical and nutritional
studies with animals (2-4).
Oxidation at Higher Temperatures: Although the rate of
oxidation is greatly accelerated at higher temperatures,
oxidative reactions which occur at higher temperatures
may not follow precisely the same routes and mechanisms
as the reactions at room temperatures. Thus, differences in
the stability of fats and oils often become more apparent
when the fats are used for frying or slow baking. The more
unsaturated the fat or oil, the greater will be its
susceptibility to oxidative rancidity. Predominantly
unsaturated oils such as soybean, cottonseed, or corn oil
are less stable than predominantly saturated oils such as
coconut oil. Methylsilicone often is added to institutional
frying fats and oils to reduce oxidation tendency and
foaming at elevated temperatures. Frequently, partial
hydrogenation is employed in the processing of liquid
vegetable oil to increase the stability of the oil. Also
oxidative stability has been increased in many of the oils
developed through biotechnological engineering. The
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
stability of a fat or oil may be predicted to some degree by
the oxidative stability index (OSI).
Polymerization of Fats: All commonly used fats and
particularly those high in polyunsaturated fatty acids tend
to form some larger molecules known broadly as polymers
when heated under extreme conditions of temperature and
time. Under normal processing and cooking conditions
polymers are formed in insignificant quantities. Although
the polymerization process is not understood completely, it
is believed that polymers in fats and oils arise by formation
of either carbon to carbon bonds or oxygen bridges
between molecules. When an appreciable amount of
polymer is present, there is a marked increase in viscosity.
Animal studies have shown that any polymers that may be
present in a fat or oil are absorbed poorly from the
intestinal tract and are excreted as such in the feces.
Reactions during Heating and Cooking: Glycerides are
subject to chemical reactions (oxidation, polymerization,
and hydrolysis) which can occur particularly during deep
fat frying. The extent of these reactions, which may be
reflected as a decrease in iodine value of the fat and an
increase in free fatty acids, depends on the frying
conditions, principally the temperature, aeration, and
duration. The composition of a frying fat also may be
affected by the kind of food being fried. For example, when
frying high fat foods such as chicken, some fat from the
food will be rendered and blend with the frying fat and
some frying fat will be absorbed by the food. In this manner
the fatty acid composition of the frying fat will change as
frying progresses. Since absorption of fat by the fried food
may be extensive, it is often necessary to replenish the
fryer with fresh fat. This replacement with fresh fat tends
to dilute overall compositional changes of the fat during
prolonged frying. Frying conditions do not, however,
saturate the unsaturated fatty acids, although the ratio of
saturated to unsaturated fatty acids will change due to
some polymerization of unsaturated fatty acids. It is the
usual practice to discard frying fat when prolonged frying
causes excessive foaming of the hot fat, the fat tends to
smoke excessively, usually from prolonged frying with low
fat turnover, or an undesirable flavor or dark color
develops. Any or all of these qualities associated with the
fat can decrease the quality of the fried food.
The "smoke," "flash," and "fire points" of a fatty material
are standard measures of its thermal stability when heated
in contact with air. The smoke point is the temperature at
which smoke is first detected in a laboratory apparatus
protected from drafts and provided with special
illumination. The temperature at which the fat smokes
freely is usually somewhat higher. The flash point is the
temperature at which the volatile products are evolved at
such a rate that they are capable of being ignited but not
capable of supporting combustion. The fire point is the
temperature at which the volatile products will support
continued combustion. For typical fats with a free fatty acid
content of about 0.05%, the smoke, flash, and fire points
are around 420º, 620º, and 670º F, respectively. The
degree of unsaturation of an oil has little, if any, effect on its
smoke, flash, or fire points. Oils containing fatty acids of
low molecular weight such as coconut oil, however, have
lower smoke, flash, and fire points than other animal or
vegetable fats of comparable free fatty acid content. Oils
subjected to extended use will have increased free fatty
acid content resulting in a lowering of the smoke, flash and
fire points. Accordingly used oil freshened with new oil will
show an increased smoke, flash and free points. It is
important to note that all oils will burn if overheated. So,
careful attention must be given to all frying operations. The
continuous generation of smoke from a frying pan or deep
fryer is a good indication that the fat is being overheated
and could ignite if high heating continues. Considerable
work has been done studying the effects of elevated
temperatures on the composition and biological qualities of
edible fats and oils. Much of this work has been done with
temperatures and other conditions which simulated those
experienced in commercial deep frying operations.
CHEMICAL TEST AND ANALYSIS FOR IDENTIFICATION
OF FATTY OILS
There are a number of quality control parameters for the
assessment of quality of lipid drugs mentioned in various
pharmacopoeias like: refractive index, specific gravity,
iodine value, saponification value, determination of
unsaponifiable matter, acid value, peroxide value, anisidine
value, GLC profile, fatty acid composition as well as TLC and
HPTLC fingerprints.
Analysis of Fats and oils: The analysis of oil to determine
the different values by analytical methods can be
completed by the calculation of following values.
Saponification Value: The saponification value is the
number of milligrams of potassium hydroxide necessary
to neutralize the free acids and to saponify the esters
present in 1g of the substance. The Saponification value is a
measure of the equivalent weight of the acids present and
is therefore, useful as an indication of purity. Adulteration
with mineral oils would be shown by low Saponification
value.
Acid Value: The acid value is the number, which expresses
in milligrams the amount of hydroxide necessary to
neutralize the free acids present in 1g of the substance. It is
significant for Determination of equivalent weight.
Ester Value: The ester value is the number of potassium
hydroxide required to saponify the ester present in 1g of
the substance. The ester value is used to determine the
quality of the fixed oil. Ester value = Saponification value –
Acid value.
Iodine Value: The iodine value is the number, which
expresses in grams the quantity of halogen, calculated as
iodine, which is absorbed by 100 gm of the substance
under the described conditions. Iodine value is a measure
of unsaturated compounds present in the substance or
measure of double bonds. It is also used in the substitution
reaction.
Peroxide Value: The peroxide value is the number of
milliequivalents of active oxygen that expresses the amount
of peroxide contained in 1000g of the substance.
Unsaponifiable Matter: The unsaponifiable matter
consists of substance present in oil and fast, which are not
saponifiable by alkali hydroxides, and are determined
substances being examined.
Specific Gravity: Specific gravity is defined as weight per
milliliter of the solution at a constant temperature. These
constants are used as standards for liquids, including fixed
oil, synthetic chemicals and solutions. Specific gravity of oil
=Density of oil/Density of water
Chemical tests for cholestrol, steroid and triterpenoid
glycosides (Libermann Bruchard test): Alcoholic extract
of drug was evaporated to dryness and extracted with
CHCl , add few drops of acetic anhydride followed by conc.
3
60
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
H SO from side wall of test tube to the CHCl extract.
2
4
carrier, anti-dusting agent for seasonings, spices, drink
mixes, or any powder and coating for dried fruits and nuts.
The medium-chain-triacylglycerides, or MCT, oils have
traditionally been used in special dietary formulations and
supplements. MCTs are not fully metabolized, therefore
deliver fewer calories. These oils are not hydrogenated,
hence they are trans fat-free products. There have been
reports indicating that it may be used as a replacement for
partially hydrogenated vegetable oils in bakery
applications. It is a high stability trans fat-free and shelf-life
stability of conventional all-purpose shortenings, is a line of
low- or no trans oils and shortenings designed for use in
baked goods, frying applications, confections, snacks,
cereals. Although most of these modified oils are
commercially available today, cost and production
problems hinder their use in commodity food product (5052). Palm oil can be fractionated into olein and stearine
fractions, which can be further fractionated into harder and
softer products. Some manufacturers replace hydrogenated
oils in their product with palm oil stearine (saturated fat
fraction). Both types of fats, trans fat and saturated fat,
increase low-density lipoproteins, which contribute to
atherosclerosis and high cholesterol. Hence, the
reformulated trans fat free product is not healthier than the
food containing trans fat. Palm oil crystallizes slower than
the other fats and oils. This leads to a phenomenon known
as post hardening, which the product becomes harder
during storage. Trans-free margarines prepared with
sunflower and cottonseed oils interesterified with palm oil,
palm kernel oil, palm stearine, and palm kernel olein
minimize post hardening. There are studies indicating
preparation of skim milk containing emulsifiers prior to
crystallization retards post hardening in blends containing
high palm oil and palm kernel oil. The current emphasis on
trans fat reduction in foods without compromising their
quality and taste has accelerated development of new
ingredients that can be used as trans fat replacers in a
variety of applications, such as pastries, breads, fried foods,
soups, and sauces. Such a palm-oil-based emulsifier system
with lower saturated fat content that can be used in bakery
products. This product is nonhydrogenated, hence does not
contain trans fat. This makes oil to very suitable oil for
hydrogenation (hardening) for the production of speciality
fats with different end-use melting points and hardness.
Hence their properties have to be modified in order to
extend the range of utilization (52-60). This article has
been provides useful information regarding the
composition and functional values of fats and oils. It is
intended for use by consumers, nutritionists, dieticians,
physicians, food technologists, food industries and others
having an interest in dietary fats and oils. Much research
continues on the role of dietary fat in relation to health (6070). In future, this article will be revised to keep the
information as current and useful as possible.
3
Formation of violet to blue coloured ring at the junction of
two liquid, indicate the presence of steroid moiety.
CHEMICAL TESTS FOR LIPIDS
1. Solubility in polar and nonpolar Solvents: Lipids are
insoluble in polar solvents like water and soluble in
nonpolar solvents like petroleum ether, benzene and
mineral oil.
2. Sudan IV test: Lipids stain red when Sudan IV (a
common stain) is added. Sudan IV is a lipid soluble dye.
When Sudan IV is added to a mixture of lipids and water,
the dye will move into the lipid layer and makes it red.
3. Grease Spot Test: A simplest test for lipid is based on
the ability of lipids to produce a translucent spot on paper
4. Emulsification test: If emulsifiers like bile salts, tween
or soap solution is mixed with lipids and water; the lipids
broken down into smaller fragments, which remained
suspended for long periods of time in water.
DISCUSSION AND CONCLUSION: Edible oils and fats
mainly consist of triacylglycerides, which are compounds
with three fatty acids esterified onto a glycerol backbone.
Fats and oils of animal origin, such as butter and lard, are
primarily composed of saturated fatty acids. Plant derived
oils and fats mostly contain monounsaturated and
polyunsaturated fatty acids, which include, respectively,
one or more double bonds in their chemical structure. In
the presence of oxygen, monounsaturated and
polyunsaturated fatty acids can deteriorate and go rancid.
Manufacturers can reduce deterioration and improve food
texture by partially hydrogenating the unsaturated fat (4145). Most naturally occurring unsaturated fatty acids have
cis structures at their double bonds. Hydrogenation
eliminates some double bonds and rearranges others,
converting them to the trans configuration. The extent of
hydrogenation determines how much a fat’s melting point
is raised. Thus, liquid vegetable oils are converted into
products ranging from soft margarines to solid shortenings.
A trans fat content of commercially prepared foods, and a
new Food and Drug Administration rule regarding listing of
trans fat on nutrition labels. This fact sheet focuses on the
alternatives to trans fat for food applications. Edible oil
quality is defined by its oxidative stability, functionality,
and nutritional value. Various fat modification techniques:
hydrogenation, interesterification, fractionation, and
combinations thereof are used to improve oil functionality
and stability. Plant breeding and biotechnology have also
been used extensively to develop oilseeds with required
agronomic properties and oil functionality. Over the past
several decades, a number of oilseeds have been
introduced with modified fatty acid compositions. Some of
these oilseeds are canola and soybean with low linolenic
acid content; corn, soybean, sunflower, and peanut with
high oleic acid content; and soybean with high and low
saturated fatty acid contents (46-49). Many of these oils
have potential in trans fat reduction. The solid fats which
crystallizes readily, helps aeration, and creams easily with
sugar. Its melting point and profile make it suitable for
cakes, muffins, and bakery fillings. These fats are used in
products such as chocolates/coatings, toffees, coffee
whiteners, whipped toppings, filler creams and non-dairy
products. The non hydrogenated oils with high stability and
low solid profiles. This product can be used as a flavor
61
REFERENCES
1. Hui, Y. H., ed., Bailey’s Industrial Oil and Fat Products, vol.
2, Edible Oil and Fat Products: Oils and Oilseeds, 5th ed.,
New York, John Wiley & Sons, Inc., p. 214, 1996.
2. Ed C, Nick B, Maury B, Maurice B, Carl H, Allan H, Jan H,
Tony I, Dan L, Earnie L, Don M, Gerald M, Mark N, Ed P,
Judy P, Ram R, Joe S, Stan S, Dennis S, Bob W, Laura W.
Food Fats and Oils, Institute of Shortening and Edible
Oils, 8th Edition, 1750 New York, 120, Washington, DC
20006.
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
Pariza, M. W., Conjugated linoleic acid, a newly
recognized nutrient. Chemistry & Industry, pp. 464-466,
1997.
Henderson L, Gregory J, Irving K et al., The National
Diet and Nutrition Surveys: Adults aged 19-64 years,
volume 2, Energy, protein, carbohydrate, fat and
alcohol intake, HMSO, London, 2003.
Valeille, K., Gripois, D., Blouquit, M.F., Souidi, M.,
Riottot, M., Bouthegourd, J.C., et al. 2004. Lipid
atherogenic risk markers can be more favourably
influenced by the cis-9,trans-11 octadecadienoate
isomer than a conjugated linoleic acid mixture or fish
oil in hamsters. British Journal of Nutrition, 91, 191–
199.
Mata, P., Garrido, J. A., Ordovas, J. M., Blazquez, E.,
Alvarez-Sala, L. A., Rubio, M. J., Alfonso, R., and de Oya,
M., Effect of dietary monounsaturated fatty acids on
plasma lipoproteins and apolipoproteins in women.
Am. J. Clin. Nutr., 56: 77-83, 1992.
Gardner, C. D. and Kraemer, H. C., Monounsaturated
versus polyunsaturated dietary fat and serum lipids. A
meta-analysis. Arterioscler. Thromb. Vasc. Biol., 15:
1917-1927, 1995.
Judd, J., Baer, D., Clevidence, B., Kris-Etherton, P.,
Muesing, R., Iwane, M., and Lichtenstein, A., Blood lipid
and lipoprotein modifying effects of trans
monounsaturated
fatty
acids
compared
to
carbohydrate, oleic acid, stearic acid, and C12:0-16:0
saturated fatty acids in men fed controlled diets. FASEB
J., 12: A229, 1998.
British Nutrition Foundation, Report of the British
Nutrition Foundation Task Force. Trans Fatty Acids,
London, The British Nutrition Foundation, 1995.
Ip, C., Scimeca, J. A., and Thompson, H. J., Conjugated
linoleic acid. A powerful Anti- carcinogen from animal
fat sources. Cancer, 74: 1050-1054, 1994.
Ip, C., Scimeca, J. A., and Thompson, H. J., Effect of
timing and duration of dietary conjugated linoleic acid
on mammary cancer prevention. Nutr. Cancer, 24: 241247, 1995.
Asif, M. Health effects of omega-3,6,9 fatty acids: Perilla
frutescens is a good example of plant oils. Orient Pharm
Exp Med. 2011. DOI 10.1007/s13596-011-0002-x
Decker, E.A. (1996). The role of stereospecific
saturated fatty acid positions on lipid nutrition.
Nutrition Reviews, 54(4), 108–110.
Hunter, J.E. (2001). Studies on effects of dietary fatty
acids as related to their position on triglycerides.
Lipids, 36, 655–668.
Mu, H.L. & Hoy, C.E. (2004). The digestion of dietary
triacylglycerols. Progress in Lipid Research, 43(2), 105–
133.
Mensink, R.P. (2005). Metabolic and health effects of
isomeric fatty acids. Current Opinion in Lipidology, 16,
27–30.
List, G.R. (2004). Decreasing trans and saturated fatty
acid content in food oils. Food Technology, 58, 23–31.
Gavino, V.C., Gavino, G., Leblanc, M.J., & Tuchweber, B.
(2000). An isomeric mixture of conjugated linoleic acid,
but not pure cis-9,trans-11- octadecadienoic acid
affects body weight gain and plasma lipids in hamsters.
Journal of Nutrition, 130, 27–29.
U.S. Department of Agriculture and U.S. Department of
Health and Human Services, Nutrition and Your Health:
62
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
Dietary Guidelines for Americans, 4th ed., Home and
Garden Bulletin #232, Washington, D.C., 1995.
National Cholesterol Education Program, Report of the
Expert Panel on Population Strategies for Blood
Cholesterol
Reduction.
Executive
Summary,
Washington, D.C., U.S. Department of Health and
Human Services, NIH Publication 90-3047, 1990.
Fiber, lipids, and coronary heart disease. A statement
for healthcare professionals from the Nutrition
Committee, American Heart Association. Circulation,
95: 2701-2704, 1997.
Clevidence, B. A., Judd, J. T., Schaefer, E. J., Jenner, J. L.,
Lichtenstein, A. H., Muesing, R. A., Wittes, J., and Sunkin,
M. E., Plasma lipoprotein(a) levels in men and women
consuming diets enriched in saturated, cis, or trans
monounsaturated fatty acids. Arterio. Thromb. Vasc.
Biol., 17: 1657-1661, 1997.
Ascherio A, Stampfer MJ, Willett WC. "Trans fatty acids
and coronary heart disease". Retrieved on 2006-09-14.
Booyens J, Louwrens CC, Katzeff IE (1988). "The role of
unnatural dietary trans and cis unsaturated fatty acids
in the epidemiology of coronary artery disease".
Medical Hypotheses 25 (3): 175–182.
Willett WC, Ascherio A (1995). "Trans fatty acids: are
the effects only marginal?". American Journal of Public
Health 85 (3): 411–412.
Stender A, Dyerberg J & Astrup A. High levels of trans
fat in popular fast foods. New England Journal of
Medicine 354: 1650-2, 2006.
Almendingen, K., Jordal, O., Kierulf, P., Sanstad, B., and
Pedersen, J. I., Effects of partially hydrogenated fish oil,
partially hydrogenated soybean oil, and butter on
serum lipoproteins and Lp[a] in men. J. Lipid Res., 36:
1370-1384, 1995.
Agricultural Research Service, U.S. Department of
Agriculture, Data Tables: Results from USDA’s 1994-96
Continuing Survey of Food Intakes by Individuals and
1994-96 Diet and Health Knowledge Survey, Riverdale,
MD, p. 12, 1997.
Hunter, J. E. and Applewhite, T. H., Correction of
Dietary Fat Availability Estimates for Wastage of Food
Service Deep-Frying Fats. J. Am. Oil Chem. Soc., 70: 613617, 1993.
Noakes, M. & Clifton, P.M. (1998). Oil blends containing
partially hydrogenated or interesterified fats:
Differential effects on plasma lipids. Am J Clin Nutr, 68,
242–247.
Meijer, G.W. & Westrate, J.A. (1997). Interesterification
of fats in margarine: Effect on blood lipids, blood
enzymes, and hemostasis parameters. Eur J Clin Nutr,
51, 527–534.
Sundram K, Karupaiah T, Hayes K. (2007). "Stearic
acid-rich interesterified fat and trans-rich fat raise the
LDL/HDL ratio and plasma glucose relative to palm
olein in humans.". Nutr Metab 4: 3.
Karabulut, I., Turan, S., & Ergin, G. (2004). Effects of
chemical interesterification on solid fat content and
slip melting point of fat/oil blends. European Food
Research and Technology, 218, 224–229.
Kubow, S. (1996). The influence of positional
distribution of fatty acids in native, interesterified and
structure-specific lipids on lipoprotein metabolism and
atherogenesis. Journal of Nutritional Biochemistry, 7,
530–541.
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
35. Chin, S. F., Liu, W., Storkson, J. M., Ha, Y. L., and Pariza,
M. W., Dietary sources of conjugated dienoic isomers of
linoleic acid, a newly recognized class of
anticarcinogens. J. Food Comp. Anal., 5: 185-197, 1992.
36. Decker, E. A., The role of phenolics, conjugated linoleic
acid, carnosine, and pyrroloquinoline quinone as
nonessential dietary antioxidants. Nutr. Revs., 53: 4958, 1995.
37. Allison, D. B., Egan, K., Barraj, L. M., Caughman, C.,
Infante, M., and Heimbach, J. T., Estimated intakes of
trans fatty and other fatty acids in the U.S. population. J.
Am. Diet. Assoc., 99: 166-174, 1999.
38. Reducing Trans Fat in the Diet Robert M. Reeves,
President, Institute of Shortening and Edible Oils,
Washington, D.C. February 24, 2005, U.S. Dietary
Guidelines. 2005.
39. Belury, M. (2002). Not all trans-fatty acids are alike:
What consumers may lose when we oversimplify
nutrition facts. Journal of the American Dietetic
Association, 102, 1606.
40. Bracco, U. (1994). Effect of triglyceride structure on
fat-absorption. American Journal of Clinical Nutrition,
60(Suppl S), S1002–S1009.
41. Gaullier, J.M., Halse, J., Hoye, K., Kristiansen, K.,
Fagertun, H., Vik, H., & Gudmundsen, O. (2004).
Conjugated linoleic acid supplementation for 1 year
reduces body fat mass in healthy overweight humans.
American Journal of Clinical Nutrition, 79, 1118–1125.
42. Aro, A., Jauhiainen, M., Partanen, R., Salminen, I., and
Mutanen, M., Stearic acid, trans fatty acids, and dairy
fat: effects on serum and lipoprotein lipids,
apolipoproteins, lipoprotein(a), and lipid transfer
proteins in healthy subjects. Am. J. Clin. Nutr., 65: 14191426, 1997.
43. Gardner, C. D., Fortmann, S. P., and Krauss, R. M.,
Association of small low-density lipoprotein particles
with the incidence of coronary artery disease in men
and women. J. Am.Med. Assn., 276: 875-881, 1996.
44. Zock, P. L. and Katan, M. B., Linoleic acid intake and
cancer risk: a review and meta-analysis. Am. J. Clin.
Nutr., 68: 142-153, 1998.
45. Hunter, J. E., and Applewhite, T. H., Reassessment of
trans fatty acid availability in the U.S. diet. Am J. Clin.
Nutr., 54: 363-369, 1991.
46. Kris-Etherton, P. M. and Nicolosi, R. J., Trans Fatty Acids
and Coronary Heart Disease Risk, Washington D.C.,
International Life Sciences Institute, 1995.
47. ASCN/AIN Task Force on Trans Fatty Acids, Position
paper on trans fatty acids. Am. J. Clin. Nutr., 63: 663670, 1996.
48. Mensink R. P. and Katan, M. B., Effects of dietary trans
fatty acids on high-density and lowdensity lipoprotein
cholesterol levels in healthy subjects. N. Engl. J. Med.,
323: 439-445, 1990.
49. Judd, J. T., Clevidence, B. A., Muesing, R. A., Wittes, J.,
Sunkin, M. E., and Podczasy, J. J., Dietary trans fatty
acids: effects on plasma lipids and lipoproteins of
healthy men and women. Am. J. Clin. Nutr., 59: 861-868,
1994.
50. Willett, W. C., Stampfer, M. J., Manson, J. E., Colditz, G. A.,
Speizer, F. E., Rosner, B. A., Sampson, L. A., and
Hennekens, C. H., Intakes of trans fatty acids and risk of
coronary heart disease among women. Lancet 341:
581-585, 1993.
63
51. Emken, E. A., ed., Trans fatty acids: infant and fetal
development. Report of an Expert Panel on Trans Fatty
acids and Early Development, Am. J. Clin .Nutr., 66:
715S -736S, 1997.
52. Chin, S. F., Liu, W., Storkson, J. M., Ha, Y. L., and Pariza,
M. W., Dietary sources of conjugated dienoic isomers of
linoleic acid, a newly recognized class of
anticarcinogens. J. Food Comp. Anal., 5: 185-197, 1992.
53. Ha, Y. L., Grimm, N. K., and Pariza, M. W.,
Anticarcinogens from fried ground beef: heataltered
derivatives of linoleic acid. Carcinogenesis, 8: 18811887, 1987.
54. Lee, K. N., Kritchevsky, D., and Pariza, M. W.,
Conjugated linoleic acid and atherosclerosis in rabbits.
Atherosclerosis, 108: 19-25, 1994.
55. Nicolosi, R. J., Rogers, E. J., Kritchevsky, D., Scimeca, J.
A., and Huth, P. J., Dietary conjugated linoleic acid
reduces plasma lipoproteins and early atherosclerosis
in hypercholesterolemic hamsters. Artery, 22: 266-277,
1997.
56. Park, Y., Albright, K. J., Liu, W., Storkson, J. M., Cook, M.
E., and Pariza, M. W., Effect of conjugated linoleic acid
on body composition in mice. Lipids, 32: 853-858,
1997.
57. Trans fat: Avoid this cholesterol double whammy".
Mayo Foundation for Medical Education and Research
(MFMER). 2007.
58. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ,
Willett WC (2006). "Trans Fatty Acids and
Cardiovascular Disease". New England Journal of
Medicine 354 (15): 1601–1613.
59. Hu, FB; Stampfer, MJ, Manson, JE, Rimm, E, Colditz, GA,
Rosner, BA, Hennekens, CH, Willett, WC (1997).
"Dietary fat intake and the risk of coronary heart
disease in women" (PDF). New England Journal of
Medicine 337 (21): 1491–1499.
60. Willett WC, Stampfer MJ,Manson JE, Colditz GA, Speizer
FE, Rosner BA, Sampson LA, Hennekens CH. Intake of
trans fatty acids and risk of coronary heart disease
among women. Lancet 341: 581-5, 1993.
61. Mozaffarian D, Katan MB, Ascherio A, Stampfer MJ &
Willett WC, Trans fatty acids and cardiovascular
disease. New England Journal of Medicine 354: 160113, 2006.
62. Larsen, T.M., Soren, T., & Astrup, A. (2003). Efficacy and
safety of dietary supplements containing CLA for the
treatment of obesity: Evidence from animal and human
studies. Journal of Lipid Research, 44, 2234–2241.
63. Malpuech-Brugére, C., Verboeket-van de Venne,
W.P.H.G., Mensink, R.P., Arnal, M.A., Morio, B.,
Brandolini, M., et al. (2004). Effects of two conjugated
linoleic acid isomers on body fat mass in overweight
humans. Obesity Research, 12, 591–598.
64. Meijer, G.W., Tol, A. van, Berkel, T.J.C. van, &
Weststrate, J.A. (2001). Effect of dietary elaidic versus
vaccenic acid on blood and liver lipids in the hamster.
Atherosclerosis, 157, 31–40.
65. Mensink, R.P., Zock, P.L., Kester, A.D., & Katan, M.B.
(2003). Effects of dietary fatty acids and carbohydrates
on the ratio of serum total to HDL cholesterol and on
serum lipids and apo lipoproteins: A meta-analysis of
60 controlled trials. Am J Clin Nutr, 77, 1146–1155.
66. Moloney, F., Yeow, T.P., Mullen, A., Nolan, J.J., & Roche,
H.M. (2004). Conjugated linoleic acid supplementation,
insulin sensitivity, and lipoprotein metabolism in
Mohammad asif et. al/ General Chemistry, Composition, Identification and Qualitative Tests of Fats or Oils
patients with type 2 diabetes mellitus. American
Journal of Clinical Nutrition, 80, 887–895.
67. Noone, E.J., Roche, H.M., Nugent, A.P., & Gibney, M.J.
(2002). The effect of dietary supplementation using
isomeric blends of conjugated linoleic acid on lipid
metabolism in healthy human subjects. British Journal
of Nutrition, 88, 243–251.
68. Oomen, C.M., Ocke, M.C., Feskens, E.J., Erp-Baart, M.A.
van, Kok, F.J., & Kromhout, D. (2001). Association
between trans fatty acid intake and 10-year risk of
coronary heart disease in the Zutphen Elderly Study: A
prospective population-based study. Lancet, 357, 746–
751.
69. Turpeinen, A.M., Mutanen, M., Aro, A., Salminen, I.,
Basu, S., Palmquist, D.L., & Griinari, M. (2002).
Bioconversion of vaccenic acid to conjugated linoleic
acid in humans. American Journal of Clinical Nutrition,
76, 504–510.
70. Weggemans, R.M., Rudrum, M., & Trautwein, E.A. 2004.
Intake of ruminant versus industrial trans fatty acids
and risk of coronary heart disease—what is the
evidence? European Journal of Lipid Science and
Technology, 106, 390–391
64