3.2 Fatty Acids 159taste substances and numerous odor substances.
On the whole, fats enrich the nutritional quality
and are of importance in food to achieve the de-
sired texture, specific mouthfeel and aroma, and
a satisfactory aroma retention. In addition, foods
can be prepared by deep frying, i. e. by dipping
the food into fat or oil heated to a relatively high
temperature.
The lipid class of compounds also includes some
important food aroma substances or precursors
which are degraded to aroma compounds. Some
lipid compounds are indespensable as food emul-
sifiers, while others are important as fat- or oil-
soluble pigments or food colorants.
3.2 FattyAcids.............................................
3.2.1 NomenclatureandClassification...........................
Acyl lipid hydrolysis releases aliphatic car-
boxylic acids which differ in chemical structure.
They can be divided into groups according to
chain length, number, position and configuration
of their double bonds, and the occurrence of
additional functional groups along the chains.
The fatty acid distribution pattern in food is
another criterion for differentiation.
Table 3.2 compiles the major fatty acids which
occur in food. Palmitic, oleic and linoleic acids
frequently occur in higher amounts, while the
other acids listed, though widely distributed, as
a rule occur only in small amounts (major vs mi-
nor fatty acids). Percentage data of acid distribu-
tion make it obvious that unsaturted fatty acids
are the predominant form in nature.
Table 3.2.Structures of the major fatty acids
Abbreviated
designation Structurea Common name Proportion (%)b
14:0 Myristic acid 2
16:0 Palmitic acid 11
18:0 Stearic acid 4
18:1(9) Oleic acid 34
18:2(9,12) Linoleic acid 34
18:3(9, 12, 15) Linolenic acid 5
aNumbering of carbon atoms starts with carboxyl group-C as number 1.
bA percentage estimate based on world production of edible oils.
Fatty acids are usually denoted in the literature
by a “shorthand description”, e. g. 18:2 (9, 12)
for linoleic acid. Such an abbreviation shows the
number of carbon atoms in the acid chain and
the number, positions and configurations of the
double bonds. All bonds are considered to be cis;
whenever trans-bonds are present, an additional
“tr” is shown. As will be outlined later in a de-
tailed survey of lipid structure, the carbon skele-
ton of lipids should be shown as azigzagline
(Table 3.2).3.2.1.1 SaturatedFattyAcids
Unbranched, straight-chain molecules with an
even number of carbon atoms are dominant
among the saturated fatty acids (Table 3.6).
The short-chain, low molecular weight fatty
acids (<14:0) are triglyceride constituents
only in fat and oil of milk, coconut and palm-
seed. In the free form or esterified with low
molecular weight alcohols, they occur in nature
only in small amounts, particularly in plant
foods and in foods processed with the aid
of microorganisms, in which they are aroma
substances.
Odor and taste threshold values of fatty acids are
compiled in Table 3.3 for cream, butter and cocoa
fat. The data for cream and coconut fat indicate
lower odor than taste threshold values of C 4 -and
C 6 -fatty acids, while it is the reverse for C 8 -upto
C 14 -fatty acids.
The aroma threshold increases remarkably with
higher pH-values (Table 3.4) since only the
undissociated fatty acid molecule is aroma active.