Food Chemistry

212 3 Lipids

Table 3.35.Products obtained by non-enzymic degradation of linoleic acid hydroperoxides

Producta Hydroperoxide interaction with

Fe^3 + Hemo- Soya Pea Wheat flour

cysteine globin homogenate homogenate

+++ +

+++++

++

+++

++

+++

+

+ +++

aAs 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–ProteinComplexes.................................

Studies related to the interaction of hydroperox-
ides with proteins have shown that, in the ab-
sence 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 path-
ways. The thiyl radical, derived from cysteine
byabstractionofanH-atom,isaddedtothe
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-octa-

decadienoic acid not bittera

9-Hydroperoxy-trans-10,cis-12-octa-

decadienoic acid not bittera

13-Hydroxy-cis-9, trans-11-octa-

decadienoic acid 7 .6–8. 5 a

9-Hydroxy-trans-10,cis-12-octa-

decadienoic acid 6 .5–8. 0 a

9,12,13-Trihydroxy-trans-10-octa-

decenoic acid 0 .6–0. 9 b

9, 10, 13-Trihydroxy-trans-11-octa-

decenoic acid

⎫

⎪⎪

⎬

⎪⎪

⎭

aA burning taste sensation.

bA blend of the two trihydroxy fatty acids was as-

sessed.