Food Biochemistry and Food Processing (2 edition)

(Steven Felgate) #1

BLBS102-c01 BLBS102-Simpson March 21, 2012 11:8 Trim: 276mm X 219mm Printer Name: Yet to Come


12 Part 1: Principles/Food Analysis

Table 1.6.Proteolytic Changes in Cheese Manufacturing

Enzyme Reaction

Coagulation
Chymosin (rennin, EC 3.4.23.4) κ-Casein→Para-κ-casein+Glycopeptide, similar to pepsin A
Proteolysis
Proteases Proteins→High-molecular-weight peptides+Amino Acids
Amino peptidases, dipeptidases, tripeptidases Low molecular weight peptides→Amino acids
Proteases, endopeptidases, aminopeptidases High-molecular weight peptides→Low molecular weight peptides
Decomposition of amino acids
Aspartate transaminase (EC 2.6.1.1) l-Asparate+2-Oxoglutarate→Oxaloacetate+l-Glutamate
Methionineγ-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→α-Ketoglutarate
Serine→Pyruvate
Threonine→α-Ketobutyrate

Source:Schormuller 1968, Kilara and Shahani 1978, Law 1984a, 1984b, Grappin et al. 1985, Gripon 1987, Kamaly and Marth 1989, Khalid and
Marth 1990, Steele 1995, Walstra et al. 1999 (www.iubmb.org).

Table 1.7.Protein Degradation in Germinating Seeds

Enzyme Reaction

Aminopeptidase (EC 3.4.11.xx) Neutral or aromatic aminoacyl-peptide+H 2 O→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

Source: Stauffer 1987a, 1987b, Bewley and Black 1994, IUBMB-NC website (www.iubmb.org).

Table 1.8.Amino Acid Modifications

Amino Acid Modification Product

Arginine Deamination Citrulline
Glutamine Deamination Glutamic acid
Asparagine Deamination Aspartic acid
Various C-terminal amidation Amidated amino acid/protein
Serine Phosphorylation Phosphoserine
Histidine Phosphorylation Phosphohistidine
Tyrosine Phosphorylation Phosphotyrosine
Threonine Phosphorylation Phosphothreonine
Asparagine Glycosylation Various;N-linked glycoprotein
Serine Glycosylation Various;O-linked glycoprotein
Threonine Glycosylation Various;O-linked glycoprotein
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