3.7 Changes in Acyl Lipids of Food 211Table 3.34.Occurrence and properties of various hydroperoxide-lyases
Occurrence Substrate Products of the
catalyses
Apple, tomato, 13(S)-hydroperoxy-9-cis,11- hexanal + 12-oxo-
cucumber, tea leaf trans-octadecadienoic 9-cis-dodecenoic
(chloroplasts), soy acid (13-LOOH) acid
beans, grape
Apple, tomato, 13(S)-hydroperoxy-9-cis,11- (Z)-3-hexenal +
cucumber, tea leaf trans, 15-cis-octadecatrienoic 12-oxo-9-cis-
(chloroplasts), soy acid (13-LnOOH) dodecenoic acid
beans, grape
Cucumber, pear 9(S)-hydroperoxy-10-trans, 12-cis- (Z)-3-nonenal +
octadecadienoic acid (9-LOOH) 9-oxo-nonanoicacid
Cucumber, pear 9(S)-hydroperoxy-8-trans, 12-cis, (Z,Z)-3,6-nonadienal +
15-cis-octadecatrienoic acid 9-oxononanoic acid
(9-LnOOH)
Champignon 10(S)-hydroperoxy-10-trans, 12-cis- 1-octen-3(R)-ol +
octadecadienoic acid (10-LOOH) 10-oxo-8-trans-
Champignon 10(S)-hydroperoxy-8-trans,12- dcenoic acid (Z)-1,5-
cis-15-cis-octadecatrienoic octadien-3(R)-ol+
acid (10-LnOOH) 10-oxo-8-trans-
decenoicacid
acid. Since hydroxy but not hydroperoxy acids
taste bitter, this reaction should contribute to the
bitter taste generated during the storage of oats
(cf. 15.2.2.3).
3.7.2.4 Hydroperoxide–ProteinInteractions........................
3.7.2.4.1 Products Formed from Hydroperoxides
Hydroperoxides formed enzymatically in food
are usually degraded further. This degrada-
tion can also be of a nonenzymatic nature. In
nonspecific reactions involving heavy metal
ions, heme(in) compounds or proteins, hy-
droperoxides are transformed into oxo, expoxy,
mono-, di- and trihydroxy carboxylic acids
(Table 3.35). Unlike hydroperoxides, i. e. the
primary products of autoxidation, some of
these derivatives are characterized as having
a bitter taste (Table 3.35). Such compounds
are detected in legumes and cereals. They may
play a role in other foods rich in unsaturated
fatty acids and proteins, such as fish and fish
products.
In order to clarify the formation of the com-
pounds presented in Table 3.35, the reaction
sequences given in Fig. 3.32 have been assumed
to occur. The start of the reaction is from the
alkoxydiene radical generated from the 9- or
13-hydroperoxide by the catalytic action of heavy
metal ions or heme(in) compounds (cf. 3.7.2.1.7).
The alkoxydiene radical may disproportionate
into a hydroxydiene and an oxodiene fatty acid.
Frequently this reaction is only of secondary
importance since the alkoxydiene radical rear-
ranges immediately to an epoxyallylic radical
which is susceptible to a variety of radical com-
bination reactions. Under aerobic conditions the
epoxyallylic radical combines preferentially with
molecular oxygen. The epoxyhydroperoxides
formed are, in turn, subject to homolysis via an
oxyradical. A disproportionation reaction leads
to epoxyoxo and epoxyhydroxy compounds.
Under anaerobic conditions the epoxyallylic
radical combines with other radicals, e. g. hy-
droxy radicals (Fig. 3.32) or thiyl radicals
(Fig. 3.33).
Of the epoxides produced, the allylic epox-
ides are known to be particularly suscep-
tible to hydrolysis in the presence of pro-
tons. As shown in Fig. 3.32 trihydroxy
fatty acids may result from the hydroly-
sis of an allylic epoxyhydroxy com-
pound.