The Effect of Oxidative Enzymes in Foods - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 295

Linoleic acid

COOH

O

Lipoxygenase

2

Positional isomers

CH (CH ) - CH - CH= CH - CH= CH-(CH ) COOH

3 2 4 2 7

CH (CH ) - CH= CH - CH= CH - CH-(CH ) COOH

3 2 4 2 7

OOH

OOH

13-Hydroperoxides (13-OOH)

9-Hydroperoxides (9-OOH)

Geometrical isomers

OOH

8

8

14 14

8

8

13 9

13 9

14 14

OOH OOH

OOH

13ZE-OOH

13EE-OOH

9EZ-OOH

9EE-OOH

Optical isomers

HOO H

8

14 8 8

14

8

13

9 9

13

14

14

H HOO

H

OOH HOO

H

13(R)ZE-OOH

13(R)EE-OOH 9(R)EE-OOH

9(R)EZ-OOH

+

+

+ +

H

OOH

14

8 8 8

14

8

13 9

9

13

14

14

HOO OOH

H

H H OOH

13(S)ZE-OOH 13(S)EE-OOH 9(S)EE-OOH

9(S)EZ-OOH

FIGURE 9.2 Positional, geometrical, and optical isomers of peroxy linoleic acid.

hydroperoxyl isomers. Theoretically such isomers are possible from each cis-1,4-
pentadiene configuration ( Figure 9.2 ).
In an “anaerobic” environment due to shortage of oxygen, the E-Fe II -pentadienyl
radical complex is believed to dissociate to a free pentadienyl radical which may
then polymerize or propagate the formation of free radicals from other substrates.
However, in the anaerobic pathway the products might be oxygenated by interaction
of the pentadienyl radical with small amounts of residual hydroperoxyl or lipoxyl
radicals.
Soybean LOX-I forms the 13(S)-hydroperoxy 9(Z), 11(E)-octadecadienoic acid
from linoleic acid and the 13(S)-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic
acid from linolenic acid. The C-20 tetraenoic acid (arachidonic acid) found in animal
tissues is surprisingly oxidized to the respective 15-hydroperoxy-5-cis, 8-cis, 11-cis,
13-trans-eicosatetraenoic acid. 40 Furthermore, a range of secondary products includ-
ing dihydroperoxides arising from dioxygenation at a second site and other com-
pounds normally considered to be of mammalian origin (leucotrienes and lipoxins)
also arise from the oxidation of arachidonic acid catalyzed by soybean and potato
lipoxygenase. 41 For the type II enzymes it has been claimed for soybean LOX-II
that the 9R-hydroperoxide is formed, while for maize germ LOX has been claimed