Food Biochemistry and Food Processing

1 Food Biochemistry—An Introduction 13

Table 1.6.Proteolytic Changes in Cheese Manufacturing

Action and Enzymes Reaction
Coagulation
Chymosin (rennin, EC 3.4.23.4) -Casein →Para--casein
glycopeptide, similar to
pepsin A
Proteolysis
Proteases Proteins →high molecular weight peptides
amino acids
Amino peptidases, dipeptidases, Low molecular weight peptides →amino acids
tripeptidases
Proteases, endopeptidases, High molecular weight peptides →low molecular weight
aminopeptidases peptides
Decomposition of amino acids
Aspartate transaminase (EC 2.6.1.1) L-Asparate
2-oxoglutarate →oxaloacetate
L-glutamate
Methionine -lyase (EC 4.4.1.11) L-methionine →methanethiol
NH 3
2-oxobutanolate
Tryptophanase (EC 4.1.99.1) L-tryptophan
H 2 O →indole
pyruvate
NH 3
Decarboxylases Lysine →cadaverine
Glutamate →aminobutyric acid
Tyrosine →tyramine
Tryptophan →tryptamine
Arginine →putrescine
Histidine →histamine
Deaminases Alanine →pyruvate
Tryptophan →indole
Glutamate →
-ketoglutarate
Serine →pyruvate
Threonine →
-ketobutyrate
Sources:Schormuller 1968; Kilara and Shahani 1978; Law 1984a,b; Grappin et al. 1985; Gripon 1987; Kamaly and
Marth 1989; Khalid and Marth 1990; Steele 1995; Walstra et al. 1999; IUBMB-NC website (www.iubmb.org).

Table 1.7.Protein Degradation in Germinating Seeds

Enzyme Reaction
Aminopeptidase (EC 3.4.11.11* deleted in 1992, Neutral or aromatic aminoacyl-peptide
H 2 O →
referred to corresponding aminopeptidase) neutral or aromatic amino acids
peptide
Carboxypeptidase A (EC 3.4.17.1) Release of a C-terminal amino acid, but little or no
action with -Asp, -Glu, -Arg, -Lys, or -Pro
Sources:Stauffer 1987a,b; Bewley and Black 1994; IUBMB-NC website (www.iubmb.org).

general reactions are provided (Table 1.9). Readers
should refer to chapters 19, 20, and 26 in this book
for a detailed discussion.

LIPIDDEGRADATION INSEEDGERMINATION

During seed germination, the lipids are degraded
enzymatically to serve as energy source for plant
growth and development. Because of the presence of
a considerable amount of seed lipids in oilseeds,

they have attracted the most attention, and various

pathways in the conversion of fatty acids have been

reported (Table 1.10). The fatty acids hydrolyzed

from the oilseed glycerides are further metabolized

into acyl-CoA. From acyl-CoA, it is converted to

acetyl-CoA and eventually used to produce energy.

It is reasonable to believe that similar patterns also

exist in other nonoily seeds. Seed germination is

important in production of malted barley flour for

bread making and brewing. However, the changes of