Biomedical Engineering Reference
In-Depth Information
Linoleic acid
COOH
O
Lipoxygenase
2
OOH
COOH
COOH
13-Hydroperoxides
9-Hydroperoxides
OOH
Hydroperoxide
lyase
Hydroperoxide
lyase
CHO
CHO
CHO
Hexanal
2-Nonenal
3-Nonenal
OHC
COOH
OHC
COOH
12-Oxo-9-dodecenoic acid
9-Oxononanoic acid
OHC
COOH
CHO
12-Oxo-10-dodecenoic acid
2-Hexanal
CHO
CHO
2,6-Nonadienal
3-Hexenal
CHO
Hydroperoxide
lyase
Hydroperoxide
lyase
3,6-Nonadienal
OOH
COOH
COOH
OOH
13-Hydroperoxides
9-Hydroperoxides
O
Lipoxygenase
2
COOH
Linolenic acid
FIGURE 9.1
Possible products of the oxidation of linoleic acid catalyzed by lipoxygenase.
the action of lyases to produce the C-9 and C-6 characteristic aroma compounds,
including several aldehydes, ketones, and alcohols, many of which have low flavor
thresholds (
Figure 9.1
).
1
6
Also it is now being increasingly realized that there are other mechanisms by
which hydroperoxides can be converted into more stable products. Cleavage of the
hydroperoxide O-O bond has been observed with metalloporphyrins
17
and hetero-
lytic cleavage takes place during the reaction of cytochrome P-450 enzymes.
18
Wilcox and Marnett
19
have shown in the presence of porphyrins that cleavage of the
O-O bond can give rise to both heterolytic and homolytic products which include
the corresponding alcohols, aldehydes, and ketones. More recently, another type of
enzyme, a peroxygenase, has been described which uses unsaturated acyl hydro-
peroxides as an oxidant that catalyzes the reduction of hydroperoxides by a hetero-
lytic mechanism leading to a ferryl-oxo complex analogous to peroxidase compound
I. Soybean peroxygenase is a ferrihemoprotein and has been shown to catalyze both
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