164 3 Lipids
Table 3.9.Taste of unsaturated fatty acids emulsified in
water
Compound Threshold Quality
(mmol/1)
Oleic acid 9–12 bitter, burning,
pungent
Elaidic acid 22 slightly burning
Linoleic acid 4–6 bitter, burning,
pungent
Linolelaidic acid 11–15 bitter, burning,
scratchy
γ-Linolenic
acid 3–6 bitter, burning,
pungent
α-Linolenic acid 0.6–1. 2 bitter, burning,
pungent, like fresh
walnut
Arachidonic acid 6–8 bitter,repugnant
off-taste
3.2.1.3 Substituted Fatty Acids.
Hydroxy Fatty Acids.Ricinoleic acid is the best
known of the straight-chain hydroxy fatty acids.
Its structure is 12-OH, 18:1 (9). It is an optically
active acid with a D(+)-configuration:
(3.1)Ricinoleic acid is the main acid of castor bean oil,
comprising up to 90% of the total acids. Hence, it
can serve as an indicator for the presence of this
oil in edible oil blends.
D-2-Hydroxy saturated 16:0 to 25:0 fatty
acids with both even and odd numbers of
carbons in their chains occur in lipids in
green leaves of a great number of vegeta-
bles. γ-or∂-Lactones are obtained from
4- and 5-hydroxycarboxylic acids (C 8 to C 16 )
by the elimination of water. ∂-Lactones
have been found in milk fat and fruits.
They are very active aroma components
(cf. 5.3.2.3).
Oxo Fatty Acids.Natural oxo (or keto) acids are
less common than hydroxy acids. About 1% of
milk fat consists of saturated (C 10 –C 24 ) oxo fatty
acids, with an even number of carbon atoms, in
which the carbonyl group is located on C-5 to C-
13: One of 47 identified compounds of this sub-
stance class has the following structure:(3.2)Furan Fatty Acids.These occur in fish liver oil in
a range of 1–6% and up to 25% in some fresh-
water fish. Furan fatty acids are also part of the
minor constituents of some plant oils and but-
ter (Table 3.10). They are also present in fruits
(lemon, strawberry), vegetables (cabbage, potato)
and mushrooms (champignons).
Two of these acids have the following formulas(3.3)Photooxidation (cf. 3.7.2.1.4) of these acids can
deteriorate especially the quality of soybean oil.
Substituted fatty acids are also derived by autox-
idation or enzymatic peroxidation of unsaturated
fatty acids, which will be dealt with in more detail
in 3.7.2.3 and 3.7.2.4.1.Table 3.10.Examples for the occurrence of furan fatty
acids I and II
Oil Concentration (mg/kg)
Ia IIaSoya oil 120–170 130–230
Wheat germ oil 100–130 105–150
Rapeseed oil 6–16 7–20
Corn oil 8–11 9–13
Butter 13–139 24–208
Leaves of the tea shrubb 50 713
Green teab 4 80–100
Black teab 10 159
Spinachb 86 733
aI: 10,13-epoxy-11,12-dimethyloctadeca-10,12-
dienoic acid.
II: 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoic
acid (Formula 3.3).
bValues based on dry weight.