2009_Book_FoodChemistry

212 3 Lipids
Table 3.35. Products obtained by non-enzymic degradation of linoleic acid hydroperoxides
Product a
Hydroperoxide interaction with
Fe 3+ Hemo- Soya Pea Wheat flour
cysteine globin homogenate homogenate
+ + + +
+ + + + +
+ +
+ + +
+ +
+ + +
+
+ + + +
a As a rule a mixture of two isomers are formed with R: CH 3 (CH 2 ) 4 and R ′ :(CH 2 ) 7 COOH.
3.7.2.4.2 Lipid–Protein Complexes
Studies related to the interaction of hydroperoxides
with proteins have shown that, in the absence
of oxygen, linoleic acid 13-hydroperoxide
reacts with N-acetylcysteine, yielding an adduct
of which one isomer is shown:
(3.77)
However, in the presence of oxygen, covalently
bound amino acid-fatty acid adduct formation is
significantly suppressed; instead, the oxidized
fatty acids listed in Table 3.35 are formed.
The difference in reaction products is explained
in the reaction scheme shown in Fig. 3.33 which
gives an insight into the different reaction pathways.
The thiyl radical, derived from cysteine
by abstraction of an H-atom, is added to the
epoxyallyllic radical only in the absence of
oxygen (pathway 2 in Fig. 3.33). In the presence
of oxygen, oxidation of cysteine to cysteine oxide
and of fatty acids to their more oxidized forms
(Fig. 3.32) occur with a higher reaction rate than
in the previous reaction.
Table 3.36. Taste of oxidized fatty acids
Compound
Threshold
value for
bitter taste
(mmol/1)
13-Hydroperoxy-cis-9,trans-11-octadecadienoic
acid
not bitter a
9-Hydroperoxy-trans-10,cis-12-octadecadienoic
acid
not bitter a
13-Hydroxy-cis-9, trans-11-octadecadienoic
acid
7.6–8.5 a
9-Hydroxy-trans-10,cis-12-octadecadienoic
acid
⎫ 6.5–8.0 a
9,12,13-Trihydroxy-trans-10-octadecenoic
acid
0.6–0.9 b
⎪⎬
9, 10, 13-Trihydroxy-trans-11-octadecenoic
⎪⎭
acid
a A burning taste sensation.
b A blend of the two trihydroxy fatty acids was assessed.