Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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or a distinction may be made between oils, which are

liquid, and fats which are solid. Chemically, fats in-

clude many compounds which are fatty acids or esters

of fatty acids. However, other components are classi-

fied as lipids on the basis of their solubility properties,

even though they are not esters of fatty acids. (See

Fatty Acids: Properties.)

0002 Lipids can be classified into three groups: simple

lipids, compound lipids, and derived lipids. Simple

lipids are esters of fatty acids which produce two

classes of compounds on hydrolysis. Compound

lipids are esters of fatty acids which produce three

or more classes of compounds on hydrolysis. Derived

lipids cannot be hydrolyzed to fatty acids.

Simple Lipids

0003 The main simple lipids are triglycerides (also known

as triacylglycerols), steryl esters, and wax esters.

Hydrolysis of these lipids yields glycerol and fatty

acids, sterols and fatty acids, and fatty alcohols plus

fatty acids, respectively. The most important of these

simple lipids for food scientists are the triglycerides.

They are the major components of edible oils and

fats, often representing more than 95% of refined

oils. Triglycerides are esters of the trihydric alcohol

glycerol with three fatty acids (Figure 1). Many of the

properties of triglycerides are dependent on the com-

ponent fatty acids. Thus, the melting point of the

triglyceride reflects the melting point of the compon-

ent fatty acids, with three high-melting-point fatty

acids yielding a high-melting triglyceride. Unsatur-

ation in the fatty acids makes the triglyceride

susceptible to autoxidation, just as the fatty acid

itself would be. (See Triglycerides: Structures and

Properties.)

0004 All triglycerides are susceptible to hydrolysis in the

presence of a catalyst. Acids, bases, or enzymes belong-

ing to the hydrolase class, especially lipases, may act as

the catalyst for the hydrolysis of triglycerides.

0005Steryl esters always occur together with sterols in

plant, animal, or microbiological tissues. Wax esters

may accumulate in considerable amounts in some

biological tissues and this class comprises the main

constituent of beeswax and jojoba oil.

Compound Lipids

0006There are many members of this group. Probably the

most important compound lipids for food science are

the phospholipids.

Phospholipids

0007Phospholipids are esters of glycerol, fatty acids,

phosphoric acid, and other alcohols. The most

common phospholipids are phosphatidylcholine,

phosphatidylethanolamine, phosphatidylinositol, and

phosphatidylserine. These phospholipids share the

common features of fatty acids esterified to the 1 and

2 positions of the glycerol backbone with the phos-

phate group esterified to the 3 position (Figure 2). (See

Phospholipids: Properties and Occurrence.)

fig0001 Figure 1 Triglyceride structure. Reproduced from Lipids, En-

cyclopaedia of Food Science, Food Technology and Nutrition,

Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic

Press.

−

Phosphatidylcholine

(Lecithin)

Phosphatidylethanolamine

(Cephalin)

Phosphatidylserine

Phosphatidylinositol

Phosphatidylglycerol

OCH

N(CH

)

X =

OCH

X =

OCH

CHOHCH

OCH

CHX =

−

X =

fig0002Figure 2 Phospholipid structure. Reproduced from Lipids, En-

cyclopaedia of Food Science, Food Technology and Nutrition,

Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic

Press.

2288 FATS/Classification

0008 Whereas triglycerides occur in lipid droplets in

storage cells of plants, animals, and microorganisms,

phospholipids are the major components of cell mem-

branes. They are always present in small amounts in

edible oils extracted from biological tissues. How-

ever, the bulk of the phospholipids are removed

by degumming during the refining of edible oils.

Phospholipids differ from triglycerides in being

surface-active and they are used in food products as

emulsifiers because they migrate to the interface

between oil and water, and reduce the inter-facial

tension, thereby stabilizing an emulsion. Commercial

phospholipid preparations are called lecithin. (See

Emulsifiers: Organic Emulsifiers.)

Glycolipids

0009 Glycolipids yield fatty acids, glycerol, and carbohy-

drates on hydrolysis. Monogalactosyldiglycerides

(Figure 3) are glycolipids which are commonly

found in plant leaves and algae. They contain a high

proportion of polyunsaturated fatty acids and appear

to play a role in photosynthesis. They are also found

in the central nervous systems of some animals. Diga-

lactosyldiglycerides often accompany monogalacto-

syldiglycerides in the chloroplasts of higher plants

and algae, but generally at lower concentrations.

Mono- and digalactosyldiglycerides are surface-

active compounds which are known to play a key

role in the baking quality of wheat flour. They

assist the incorporation of air into the dough, thereby

increasing the loaf volume, and they also have

antistaling properties. (See Bread: Chemistry of

Baking.)

0010 Sulfoquinovosyldiglyceride (Figure 4) is one of the

most polar plant lipids. It occurs in the leaves of

plants, where it appears to play a role in photosyn-

thesis. It is a significant dietary lipid in green leafy

vegetables such as spinach.

0011 Cerebrosides and cerebroside sulfates are further

examples of glycolipids. These are discussed further

under sphingolipids.

Sphingolipids

0012Sphingolipids are important membrane components

in both plant and animal cells. They are present in

especially large amounts in brain and nerve tissue.

Mammalian enzymes include those which can cata-

lyze the hydrolysis of sphingolipids. If one of these

enzymes is missing, disorders known as lipidosis may

occur as the lipid accumulates in the tissues.

0013Sphingolipids (Figure 5) are derivatives of the

amino alcohol sphingosine, which is found in animal

tissues, or phytosphingosine, which is found in plant

tissues. Lipids derived from other related bases are

included in this group. Sphingosine is one of more

than 60 long-chain amino alcohols found in animals,

plants, and microorganisms. The bases commonly

contain between 12 and 22 carbon atoms in the

chain. A ceramide, which is an amide formed from a

fatty acid and sphingosine, is the characteristic parent

structure of all sphingolipids.

0014The fatty acid groups in ceramides are long-chain,

with up to 26 carbon atoms, and are commonly sat-

urated, monounsaturated, or hydroxy fatty acids. Al-

though free ceramides have been found in small

amounts in plant and animal tissues, they are gener-

ally present as a component of more complex sphin-

golipids.

0015Sphingomyelins are the most abundant sphingo-

lipids in the tissues of higher animals. The 1-hydroxyl

group of ceramide is esterified with phosphoric acid

esterified with choline or with ethanolamine.

0016Cerebrosides are glycosphingolipids which contain

a carbohydrate linked by a glycosidic linkage at the 1-

hydroxyl position of the long-chain base. Cerebro-

sides are the major sphingolipids of plants. Wheat

flour contains cerebrosides from at least four

classes of amino alcohol. Plant cerebrosides con-

tain only glucose as their component sugar, while

animal cerebrosides contain galactose, glucose,

or di-, tri- or tetrasaccharides. (See Wheat: The

Crop; Grain Structure of Wheat and Wheat-based

Products.)

CHOCOR

OCOR

fig0003 Figure 3 Monogalactosyldiglyceride structure. Reproduced

from Lipids, Encyclopaedia of Food Science, Food Technology and

Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993,

Academic Press.

CHOCOR

OCOR

fig0004Figure 4 Sulfoquinovosyldiglyceride structure. Reproduced

from Lipids, Encyclopaedia of Food Science, Food Technology and

Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993,

Academic Press.

FATS/Classification 2289

Lipoproteins

0017 Lipoproteins may also be classified as compound

lipids. These are compounds of proteins, fatty acids,

and alcohols and may include other classes. Lipids

and proteins are largely held together by hydrophobic

interactions. Transport lipoproteins and membrane

lipoproteins are important biomolecules in human

physiology. (See Lipoproteins.)

Derived Lipids

0018 This group of lipids includes a range of compounds

which vary widely in their structures. The main

derived lipids include: (1) fatty acids, (2) fat-soluble

vitamins and provitamins, (3) alcohols – including

sterols – (4) terpenoids; and (5) ethers.

Fatty Acids

0019Although simple and compound lipids are esters of

fatty acids, the free fatty acids only occur in relatively

small amounts in food and food raw materials. Edible

oils usually contain only small amounts of free fatty

acids when isolated from the plant, animal, or micro-

biological source. The concentration of free fatty

acids rises in bruised fruit such as palm fruit if the

lipases present are not inactivated rapidly by heating.

Cerebrosides (glycosides of ceramides)

Sugar is glucose or

galactose (shown),

or di- or

trisaccharide. R is as

in sphingomyelin

and other members

of homologous

series, both

saturated and

unsaturated

CH CH(CH

)

CHNHCOR

Sphingomyelin

CH CH(CH

)

CHNHCOR

O P O

R=16:0, 18:0, 24:0, 24:1

N(CH

)

Ceramides

CH CH(CH

)

CHNHCOR

Sphingosine

CH CH(CH

)

CHNH

fig0005 Figure 5 Sphingolipid structure. Reproduced from Lipids, Encyclopaedia of Food Science, Food Technology and Nutrition, Macrae R,

Robinson RK and Sadler MJ (eds), 1993, Academic Press.

2290 FATS/Classification

However, normal values of free fatty acids are below

5% in most crude edible oils. The free fatty acids

present are mixtures similar to those present in the

triglycerides. Most free fatty acids are removed from

crude edible oils during refining because of the un-

desirable effects on flavor, and the reduction of the

smoke point caused by free fatty acids. A refined oil

usually contains less than 0.1% free fatty acids.

Vitamin A

0020 Vitamin A is a C

primary alcohol occurring either

as vitamin A

or vitamin A

. The vitamin occurs in

animal and marine products such as butter (1 mg per

100 g) and eggs (3.7 mg per 100 g). It is commonly

used in the form of acetate or palmitate esters as a

food additive. Vitamin A can also be formed in vivo

from some carotenoids such as b-carotene. (See

Retinol: Properties and Determination.)

Vitamin D

0021 The term ‘vitamin D’ refers collectively to a group of

compounds derived from sterols, which are effective

in preventing the development of rickets in children.

Ergocalciferol (vitamin D

) and cholecalciferol (vita-

min D

) are the most common compounds with

vitamin D activity. Ergocalciferol is formed by

the irradiation of ergosterol with ultraviolet light

whereas cholecalciferol is formed in an analogous

manner from 7-dehydrocholesterol. (See Cholecalcif-

erol: Properties and Determination.)

Vitamin E

0022 Eight compounds belonging to the tocopherol and

tocotrienol classes have vitamin E activity. Vegetable

oils in general contain more vitamin E than animal

fats, and vegetable oils rich in polyunsaturated fatty

acids tend to be good sources of vitamin E. (See

Tocopherols: Properties and Determination.)

Vitamin K

0023 Compounds exhibiting vitamin K activity possess a 2-

methyl-1, 4-naphthoquinone ring with differing

chain-length polyprenyl substituents at the 3 position.

The dietary requirement for vitamin K by the adult

human is extremely low, because the vitamin is syn-

thesized in the intestine by intestinal bacteria. The

main dietary sources of vitamin K are green vege-

tables, which commonly contain > 100 mg per 100 g.

Carotenoids

0024 Carotenoids contribute the yellow, orange, or red

colors of many fruits and vegetables, such as carrots,

peaches, and tomatoes. They are commonly extracted

with vegetable oils, including crude palm oil, which is

a rich source containing 500 p.p.m. (See Carotenoids:

Occurrence, Properties, and Determination.)

Sterols

0025Sterols occur in the membranes of plants, animals,

and microorganisms and are termed phytosterols,

zoosterols, and mycosterols, respectively. Cholesterol

is the main zoosterol, but sterols in plants commonly

occur as mixtures with b-sitosterol, campesterol, and

stigmasterol representing three of the major phytos-

terols. These sterols are all D

-sterols (Figure 6), but

-sterols may also be present in small quantities

(Table 1). Molecules with a sterol-type structure

that lack an endocyclic double bond are termed

sterols. Methyl sterols, also known as triterpenyl

alcohol, have an additional methyl group at carbon-

4 in the A-ring of the molecule. Methyl sterols and

dimethylsterols commonly occur with sterols in plant

membranes. Bacteria usually lack sterols in their

membranes, but yeasts accumulate considerable

quantities of sterols, which may represent up to

10% of the cellular dry weight. Algae produce a

wide variety of sterols. (See Cholesterol: Properties

and Determination.)

Terpenes

0026Terpenes are oligomers or polymers of isoprene,

2-methyl-1, 3-butadiene. Monoterpenoids and

sesquiterpenoids contain 10 and 15 carbon atoms

respectively, and these components occur in essential

oils and are very important flavor compounds.

Monoterpenoids include acyclic and cyclic hydrocar-

bons, alcohols, ketones, or lactones such as myrcene,

limonene, and menthol. Sesquiterpenoids include

Cholesterol R = H

R = − C

R = − CH

R = CH − CH

R = − C

; ∆

β-Sitosterol

Stigmasterol

Campesterol

∆

-Avenasterol

Brassicasterol R = − CH

; ∆

fig0006Figure 6 Sterol structure. Reproduced from Lipids, Encyclo-

paedia of Food Science, Food Technology and Nutrition, Macrae R,

Robinson RK and Sadler MJ (eds), 1993, Academic Press.

FATS/Classification 2291

bicyclic or tricyclic compounds such as zingiberene,

which is the main constituent of the oil of ginger, or

caryophyllene, which occurs in the oil of cloves. (See

Essential Oils: Properties and Uses.)

0027 Diterpenoids include the bitter principles, which

are commonly bitter and have physiological effects.

Triterpenoids and higher terpenoids have no flavor

properties. Triterpene alcohols, which occur in small

amounts in edible oils, have been found useful in the

identification of oils in blends. Carotenoids are

the major tetraterpenoids, while chicle, which is used

in chewing gum, is the main polyterpenoid used in

foods.

Ethers

0028 Ether lipids occur in which one of the hydroxyl

groups of a diglyceride or phosphatidyl ester is linked

to an alkyl group. The alkyldiacylglycerols are

common constituents of some marine oils while

vinyl ethers or plasmalogens are found in blood.

See also: Bread: Chemistry of Baking; Carotenoids:

Occurrence, Properties, and Determination;

Cholecalciferol: Properties and Determination;

Cholesterol: Properties and Determination; Emulsifiers:

Organic Emulsifiers; Essential Oils: Properties and

Uses; Fatty Acids: Properties; Lipoproteins;

Phospholipids: Properties and Occurrence; Retinol:

Properties and Determination; Tocopherols: Properties

and Determination; Triglycerides: Structures and

Properties

Further Reading

Abu-Hadeed AM and Kotb AR (1988) A method for the

quantitative determination of individual oils in a blend.

Journal of the American Oil Chemists’ Society 65:

1922–1926.

Akoh CC and Min DB (2002) Food Lipids: Chemistry,

Nutrition and Biotechnology, 2nd edn, New York:

Marcel Dekker.

Gunstone FD (1996) Fatty Acid and Lipid Chemistry.

London: Blackie Academic & Professional.

Gunstone FD, Harwood JL and Padley FB (1994) The Lipid

Handbook, 2nd edn, London: Chapman and Hall.

Harwood JL and Russell NJ (1984) Lipids in Plants and

Microbes. London: Allen and Unwin.

Hui YH (1996) Bailey’s Industrial Oil and Fat Products,

5th edn. New York: Wiley.

Itoh T, Tamura T and Matsumoto T (1973) Sterol compos-

ition of 19 vegetable oils. Journal of the American Oil

Chemists’ Society 50: 122–125.

Ratledge C and Wilkinson SG (1988) Microbial Lipids,

vols 1, 2. London: Academic Press.

Salunkhe DK, Chavan JK, Adsule RN and Kadam SS (1992)

World Oilseeds: Chemistry, Technology, and Utilization.

New York. Van Nostrand Reinhold.

tbl0001 Table 1 Compositions of sterol fractions of 19 vegetable oils

Total sterols (%) Composition (%)

I II III IV V VI VII VIII IX X

Oil, corn 1.2 Tr

Tr 23 6 66 4 1 Tr – –

Rice bran 1.8 Tr Tr 28 15 49 5 1 2 – –

Wheat germ 2.6 Tr Tr 22 Tr 67 6 3 2 – –

Coconut 0.2 1 Tr 8 13 58 14 6 – – –

Palm 0.3 1 Tr 14 8 74 2 1 – – –

Palm kernel 0.1 3 Tr 9 11 70 6 1 Tr – –

Peanut 0.2 Tr Tr 15 9 64 8 3 1 – –

Soya bean 0.4 Tr Tr 20 20 53 3 3 1 – –

Sunflower 0.4 – – 8 8 60 4 15 4 – 1

Safflower, linoleic-rich 0.4 – Tr 13 9 52 1 20 3 2 Tr

Safflower, oleic-rich 0.4 – – 15 10 52 1 15 5 2 Tr

Olive (France) 0.2 – – 2 1 91 2 4 Tr – –

Olive (Italy) – – – 3 1 84 12 Tr Tr – –

Castor 0.3 Tr – 10 22 44 21 2 1 – –

Kapok 0.3 Tr Tr 9 2 86 2 1 – – –

Cottonseed 0.4 Tr Tr 4 1 93 2 Tr Tr – –

Linseed 0.4 1 Tr 29 9 46 13 2 – – –

Rapeseed 0.6 Tr 10 25 Tr 58 2 5 – – –

Sesame 0.6 – – 19 10 62 7 2 – – –

Cocoa butter 0.3 2 Tr 9 26 59 3 1 Tr – –

Coffee seed 1.8 Tr Tr 19 20 54 6 1 Tr – –

I. cholesterol; II. brassicasterol; III. compesterol, IV. stigmasterol; V. b-sitosterol; VI. D

-avenasterol; VII. D

-stigmasterol; VIII. D

-avenasterol; IX and X.

unidentified.

Tr, trace, less than 0.5%.

Data from Itoh T, Tamura T and Matsumoto T (1973) Sterol composition of 19 vegetable oils. Journal of the American Oil Chemists’ Society 50: 122–125.

2292 FATS/Classification

Occurrence

M H Gordon, The University of Reading, Reading, UK

Fats

0001 Fats can be extracted from biological tissues with

organic solvents. They comprise complex mixtures

of chemical classes, known as lipids, which share the

same solubility characteristics. Fats include solid fats

and liquid oils. They occur in animals, plants, and

microorganisms either as storage lipids, which are

potential sources of energy by b-oxidation, or as

membrane lipids. Storage lipids mainly comprise

triacylglycerols, whereas membrane lipids include

phospholipids, sterols, sphingolipids, and glycolipids.

(See Phospholipids: Properties and Occurrence; Tri-

glycerides: Structures and Properties.)

0002 Membrane lipids occur in cells in a phospholipid

bilayer which has been described as a fluid mosaic.

The fatty acid chains of the phospholipids are

directed towards the center of the membrane. Globu-

lar protein molecules penetrate into either side or

extend entirely across the membrane. The membrane

is considered to be asymmetric with oligosaccharide

chains protruding from glycolipids and glycoproteins

on the outer surface of the plasma membrane of

eukaryotic cells. Sterols and polar lipids are embed-

ded into the membrane. Phytosterols, including

b-sitosterol, campesterol and stigmasterol, occur

in plant cell membranes, whereas cholesterol

occurs in animal cell membranes.

Fat in Animal Products

Body Fat

0003 The bulk of the meat consumed in the UK is obtained

from sheep, cattle, and pigs, with chickens and

turkeys being major poultry products. The fat of the

adipose tissue of animals usually consists of more

than 99% acylglycerols, but fat occurring within the

muscles of animals, which are consumed as meat,

contains a considerable amount of phospholipids

and of unsaponifiable components, such as choles-

terol. Palmitic acid, stearic acid and oleic acid are

the major fatty acids present in the fat of animals

used for meat, and therefore fats derived from

animals such as lard and tallow are relatively satur-

ated (Table 1) and consequently semisolid. Fat

derived from poultry is more unsaturated. (See Fatty

Acids: Properties.)

0004The fatty acid content of depot fat (storage lipid)

varies depending on the part of the animal from

which the fat is derived. Thus, the oleic acid content

of sheep depot fat varies from 19.1 to 35.7%,

depending on the anatomical source of the fat. The

fatty acid content of depot fats in animals is also

dependent partly on the diet since de novo synthesis

in vivo supplies only part of the fatty acids. Unsatur-

ated lipids consumed by ruminants such as cattle and

sheep are hydrogenated by rumen microflora before

they are incorporated into depot fats. (See Fatty

Acids: Metabolism.)

Milk Fat

0005Bovine milk contains a complex mixture of lipids,

with triacylglycerols representing the major compon-

ent at 97–98% of the total lipid content. However,

diacylglycerols, monoacylglycerols, free fatty acids,

sterols, phospholipids, hydrocarbons, and sterol

esters are also present. The fat content of milk from

cattle reared in developed countries is in the range of

3.4–5.1%. The fatty acid composition of milk fat is

extremely complex, with over 400 fatty acids having

been identified; the major components are indicated

in Table 1. Although the level of linoleic acid (18:2) is

normally below 3% due to hydrogenation of dietary

linoleic acid in the rumen, the feeding of oil coated

with a layer of formaldehyde-treated protein has

allowed the linoleic acid content of milk fat to be

increased above 15% in experimental animals. The

fatty acid composition of milk fat varies with the

species of animal. Thus, the oleic acid content of

camel milk fat is 38.9% compared with that of

horse milk, which is 18.7%, and similar differences

are also found in other fatty acids. (See Milk: Dietary

Importance.)

tbl0001Table 1 Major fatty acids in animal fats (% w/w)

Fattyacid Lard Beeftallow Bovine milk fat

4:0 3.3

6:0 1.6

8:0 1.3

10:0 3.0

12:0 3.1

14:0 0.5–2.5 1.4–6.3 9.5

16:0 20–32 20–37 26.3

16:1 1.7–5.0 0.7–8.8 2.3

18:0 5.0–24 6–40 14.6

18:1 35–62 26–50 29.8

18:2 3.0–16 0.5–5.0 2.4

18:3 < 1.5 < 2.5 0.8

20:0 < 1.0 < 0.5

22:1

FATS/Occurrence 2293

Fat in Vegetable Products

0006 Lipids in plant materials can also be divided into

membrane lipids and storage lipids. The composition

of membrane lipids varies with membrane function.

Cytoplasmic or plasma membranes contain about

half the dry mass as lipid. Major components include

phospholipids up to 65%, glycolipids up to 20%,

sterols up to 5%, and neutral lipids including hydro-

carbons, diacylglycerols, and pigments. The main

phospholipids are phosphatidylcholine, phosphatidyl-

ethanolamine, and phosphatidylinositol. Mitochon-

drial membranes contain up to 98% of the lipids

as phospholipids. Chloroplast membranes are unique

in nature, since the major lipid components of their

lamellae are glycosylglycerides and not phospho-

lipids.

0007 Triacylglycerols occur in oil bodies, which are sur-

rounded by a monolayer or half-unit membrane. As

the oil content of seeds increases, there is a large

increase in the number of oil bodies. Lipids are stored

in the oil bodies until required as a source of energy

by the growing plant. Storage lipids from plant

sources are of considerable industrial importance,

with world production of refined plant oils exceeding

50 million tonnes per year. The commercial sources of

edible plant oils include: oilseeds, with soya bean,

rapeseed, sunflower seed, peanuts, and cottonseed

being important commercially; tree and bush prod-

ucts, including palm oil, coconut oil, olive oil, cocoa

butter, and palm kernel oil; and grains, particularly

corn oil. (See Vegetable Oils: Dietary Importance.)

0008 The oil content of the oil-bearing material (Table 2)

is one of the factors that affects the commercial util-

ization of the crop. However, other factors include

yield per hectare and ease of harvesting. In the case

of soya bean oil, the oil is a byproduct in meal pro-

duction, and therefore it is a very important oil

commercially despite having a relatively low oil con-

tent in the seed.

0009Crude vegetable oils are extracted from fruits or

seeds by pressing or by solvent extraction, usually

with hexane, and in some cases, the two processes

are applied sequentially. The extracted crude oil

contains minor lipids as well as triacylglycerols. Phos-

pholipids, sterols, sterol esters, tocopherols, free fatty

acids, diacylglycerols, carotenoids, chlorophylls and

hydrocarbons are commonly present. The fatty acid

composition of common plant oils is shown in

Table 3. There is considerable research by plant

breeders into the development of plant varieties with

modified fatty acid composition. This has led to the

development of low-erucic acid rapeseed oil, which is

considered preferable as a food oil to traditional

rapeseed oil, which has an erucic acid content of

about 45% of the total fatty acid content. Animal

experiments suggest that high levels of erucic acid

may lead to fatty lesions in heart muscles. High-oleic

sunflower oil has also been developed because of

nutritional interest in this type of oil.

Fish Oil

0010Fish can be classified as marine lean fish, marine fatty

fish and freshwater fish. Marine lean fish, including

cod, haddock, and hake, have a flesh lipid content of

0.1–1% with little seasonal variation. However,

the flesh lipid content of marine fatty fish, including

sprats, mackerel, and herring, varies from < 1 to

> 25% in some species, with considerable variation,

depending on the season and the diet. For example,

the lipid content of sprats varies from a maximum of

17% in autumn to winter and falls to about 6% in

spring to summer. Freshwater fish, including rainbow

trout, haplochromis, and rock bass, have relatively

low fish lipid contents of < 4%. (See Fish Oils: Dietary

Importance.)

0011In the flesh of lean fish such as cod, 65% of the

total lipids are phospholipids intimately associated

with muscle protein, and 35% are neutral lipids in-

cluding triacylglycerols and sterols. In the flesh of

fatty fish, a large proportion of the lipids are triacyl-

glycerols present as extracellular globules in the

muscle. Sprat flesh contains 8–15% triacylglycerols

and 0.6–1.9% phospholipids, whereas rainbow trout

contain 2.2% triacylglycerols and 0.9% phospho-

lipids. Both species also contain about 1% sterols.

The fatty acid contents of the fish lipids of several

species of fish are shown in Table 4. The unsaturated

fatty acids are commonly mixtures of positional

isomers. Fish oils are of considerable interest as

nutritional supplements because of the high level of

eicosapentaenoic (20:5) and docosahexaenoic acids

tbl0002 Table 2 Oil content of a number of oil-bearing vegetable

materials

Oil-bearingmaterial Oil content (% w/w)

Coconut 65–68

Babassu 60–65

Sesame seed 50–55

Palm fruit 45–50

Palm kernel 45–50

Peanut 45–50

Rapeseed 40–45

Sunflower seed 35–45

Safflower seed 30–35

Olive 25–30

Cottonseed 18–20

Soya bean 18–20

2294 FATS/Occurrence

(22:6) in some oils. These fatty acids are significant

because they are believed to play a role in reducing the

incidence of coronary thrombosis. Fats from marine

mammals have a similar composition to fish oil.

Microbial Oil

0012 There has been considerable interest in microbial

lipids in recent years because of the possibility of

commercial production of oils and fats from micro-

bial sources. The lipid composition of microorgan-

isms is also useful in taxonomy.

Bacteria

0013 The major lipids in Gram-positive bacteria are phos-

phatidylglycerol and phosphatidylethanolamine, in

which the acyl chains are mainly odd-numbered

branched-chain fatty acids. In contrast, Gram-

negative bacteria contain phosphatidylethanolamine

with even-numbered straight chain and cyclopropane

acyl chains. The lipids in Gram-positive bacteria are

limited to the cytoplasmic membranes and the meso-

somes, whereas in Gram-negative bacteria and myco-

bacteria, the lipids are interwoven with the external

layers of cells, and there is no clear distinction

between membrane and cell-wall lipids. The lipid

content of many species of bacteria is rather low,

although mycobacteria, corynebacteria, and nocar-

dia may contain substantial amounts, e.g., 23% in

mycobacteria grown in glycerol as the carbon

source.

Algae

0014Macroalgae such as seaweeds and phytoplankton

have low lipid contents, but microalgae grown in

the presence of light and in a nitrogen-poor medium

accumulate storage lipids rich in triacylglycerols. Oil

droplets are clearly visible in the cells. Lipid contents

as high as 70% can be achieved in algae grown under

optimum conditions for lipid biosynthesis. Some

algae may accumulate relatively high concentrations

of derived lipids of commercial interest. Thus, Duna-

liella salina accumulates more than 10% of its dry

mass as b-carotene.

Yeasts

0015Yeasts vary in oil content with low-oil, medium-oil

and high-oil types containing < 5, 5–15 and > 15% oil

as percentage cell dry weight, respectively. Oleagin-

ous yeasts have been defined as those that produce

tbl0003 Table 3 Fatty acid composition of plant oils (% w/w)

Fatty

acid

Coconut Palm

kernel

Sunflower Peanut Corn Olive Palm Cotton

seed

Soya

bean

Rapeseed Cocoa

butter

6:0 0–0.8 <1.5

8:0 5–9 3–5

10:0 6–10 3–7

12:0 44–52 40–52 <1.2

14:0 13–19 14–18 <0.5 <0.1 <1 tr 0.5–5.9 0.5–2.0 <0.5 0.9–1.2

16:0 8–11 7–9 3–10 6–15.5 8–19 8.7–18.3 32–59 17–29 7.0–12 4.5–6.0 24.2–27.0

16:0 <1 <1 <1 <1 <0.5 0.2–2.4 <0.6 0.5–1.5 <0.5

18:0 1–3 1–3 1–10 1.3–6.5 0.5–4 1.8–4.4 1.5–8.0 1.0–4.0 2.0–5.5 1.5–2.1 32.6–35.4

18:1 5–8 11–19 14–65 36–72 19–50 56.4–82.2 27–52 13–44 19–30 48.3–60.7 33.8–36.9

18:2 <2.5 0.5–2 20–75 13–45 34–62 4.2–18.9 5.0–14 33–58 48–58 18.8–22.0 2.7–4.0

18:3 <0.7 <1 <2 0.3–1.1 <1.5 0.1–2.1 4.0–12.1 9.3–10.8

20:0 <0.5 <1 <1 1–25 <1 0.2–1.3 <1 <0.5 <1.0 0.6–0.8

22:0 <1 1.5–4.8 <0.5 tr <0.5 <0.5 0.1–0.2

22:1 <0.5 <0.1 <0.5 0.1–5.1

24:0 1–2.5 <0.5 <0.5 0.2

tr, trace amount.

tbl0004 Table 4 Fatty acid composition of fish oil (% w/w)

Fatty

acid

Cod

flesh

Haddock Mackerel Sprats Rainbow

trout

Cod

liver

14:0 1.4 1.5 8.6 6.0 3.5 2.8

16:0 19.6 20.0 17.6 21.5 13.3 10.7

16:1 3.5 4.0 10.0 5.3 4.8 6.9

18:0 3.8 6.1 2.2 2.4 3.8 3.7

18:1 13.8 14.2 14.8 16.5 18.7 23.9

18:2 0.7 2.2 1.0 1.6 5.5 1.5

18:3 0.1 0.4 0.8 1.3 5.9 0.9

18:4 0.4 0.5 2.0 3.3 2.1 2.6

20:1 3.0 2.6 8.6 7.0 8.8

20:4 2.5 3.3 0.9 0.7 7.2 1.0

20:5 17.0 12.0 9.4 8.1 5.1 6.0

22:1 1.0 0.1 10.2 12.0 5.3

22:5 1.3 2.4 1.2 6.2 1.3

22:6 29.8 24.5 8.7 10.8 21.0 14.3

FATS/Occurrence 2295

>25% oil. The oil content and composition varies

between the various yeast subfamilies, and members

of a particular genus, but also varies within strains

and depends on the growth conditions. Up to 65% of

the biomass of oleaginous yeasts, e.g., Candida cur-

vata or Lipomyces spp., may comprise oil, if the yeast

is grown under nitrogen-deficient conditions.

Molds

0016 There are many examples of oleaginous molds that

accumulate > 25% oil. Oil contents up to 75% have

been described. Molds show a greater diversity of

fatty acid composition compared with yeasts, but

most species contain oleic acid, palmitic acid, and

linoleic acid as the major acids. Higher proportions

of polyunsaturated fatty acids occur in molds than in

yeasts, and molds are of interest commercially for the

production of oil containing polyunsaturated fatty

acids of nutritional interest. Thus, Mucor javanicus

has been used to produce an oil containing g-linolenic

acid, which has been sold as a nutritional supplement

in health food shops.

Fat in Processed Foods

0017 As well as occurring naturally in the membranes of

all biological tissues, fats are important in the

production of processed foods. The major industrial

applications of edible oils and fats are in frying oils,

margarine, bakery fats, shortenings, mayonnaise,

salad dressings, peanut butter, chocolate, and confec-

tionery products. The oil acts as a heat transfer

medium for frying, and it has a major effect on the

texture and flavor of the processed foods. Fat-soluble

vitamins and pigments are also present in the foods.

(See Fats: Uses in the Food Industry.)

0018 Phospholipids in the form of commercial lecithin

are another class of lipids added to processed foods.

Lecithin is added in baking formulations, cake mixes,

chocolate, confectionery products, icecream, instant

foods, margarine, nondairy toppings, and shorten-

ings. The lecithin in these products affects the texture

by improving the shortening effect of fat, stabilizing

emulsions, reducing the viscosity of sugar in fat dis-

persions, improving the wettability and dispersion of

powders in aqueous solutions, and assisting with

foam stabilization.

0019Other lipids are also important as surfactants or

emulsifiers in foods. Thus, mixtures of mono- and

diglycerides are the most common emulsifiers used

in foods to stabilize water-in-oil emulsions. They

also have various roles as surfactants, including

retarding the staling of bread, improving the behavior

of foods during extrusion cooking, improving the

palatability and reducing the stickiness of caramels

and toffees, and improving the dispersion of coffee

whiteners. Other lipid surfactants include acetylated

monoglycerides, sucrose esters, sorbitan esters and

polyoxyethylene sorbitan esters. (See Emulsifiers:

Organic Emulsifiers.)

See also: Emulsifiers: Organic Emulsifiers; Fats: Uses in

the Food Industry; Fatty Acids: Properties; Metabolism;

Fish Oils: Dietary Importance; Milk: Dietary Importance;

Vegetable Oils: Dietary Importance