Food Biochemistry and Food Processing

1 Food Biochemistry—An Introduction 17

et al. 2000). Table 1.14 gives the series of reactions
in the biosynthesis of naringenin chalcone. Naring-
enin chalcone is the building block for flavonoid
biosynthesis. The pathway for the biosynthesis of a
stilbene pinosylvin and 3,4’5’-trihydroxystilbene
has been postulated (IUBMB website).

SELECTED BIOCHEMICAL
CHANGES IMPORTANT IN THE
HANDLING AND PROCESSING OF
FOODS

PRODUCTION OFAMMONIA AND
FORMALDEHYDE FROMTRIMETHYLAMINE AND
ITSN-OXIDE

Trimethylamine and its N-oxide have long been
used as indices for freshness in fishery products.
Degradation of trimethylamine and its N-oxide leads
to the formation of ammonia and formaldehyde with
undesirable odors. The pathway on the production of
formaldehyde and ammonia from trimethylamine
and its N-oxide is shown in Figure 1.2.

PRODUCTION OFBIOGENICAMINES

Most live pelagic and scombroid fish (e.g., tunas,
sardines, and mackerel) contain an appreciable
amount of histidine in the free state. In postmortem
scombroid fish, the free histidine is converted by the
bacterial enzyme histidine decarboxylase into free
histamine. Histamine is produced in fish caught 40–
50 hours after death when fish are not properly
chilled. Improper handling of tuna and mackerel
after harvest can produce enough histamine to cause
food poisoning (called scombroid or histamine poi-
soning). The common symptoms of this kind of food
poisoning are facial flushing, rashes, headache, and

gastrointestinal disorder. These disorders seem to be

strongly influenced by other related biogenic amines,

such as putrescine and cadaverine, produced by sim-

ilar enzymatic decarboxylation (Table 1.15). The

Table 1.14.Naringenin Chalcone Biosynthesis

Enzyme Reaction
Phenylalanine ammonia-lyase (EC 4.3.1.5) L-phenylalanine →trans-cinnamate
NH 3
Trans-cinnamate 4-monoxygenase (EC 1.14.13.11) Trans-cinnamate
NADPH 2
O 2 →4-
hydroxycinnamate
NADP
H 2 O
4-Coumarate-CoA ligase (EC 6.2.1.12) 4-hydroxycinnamate (4-coumarate)
ATP
CoA
→4-coumaroyl-CoA
AMP
diphosphate
Naringinin-chalcone synthase (EC 2.3.1.74) 4-coumaroyl-CoA
3 malonyl-CoA →naringinin
chalcone
4 CoA
3 CO 2
Sources:Eskin 1990, Croteau et al. 2000, IUBMB-NC Enzyme website (www.iubmb.org).

Figure 1.2.Degradation of trimethylamine and its N-

oxide. Trimethylamine N-oxide reductase (EC 1.6.6.9),

Trimethylamine dehydrogenase (EC 1.5.8.2),

Dimethylamne dehydrogenase (EC 1.5.8.1), Amine

dehydrogenase (EC 1.4.99.3). [Haard et al. 1982,

Gopakumar 2000, Stoleo and Rehbein 2000, IUBMB-

NC website (www.iubmb.org)]