Food Biochemistry and Food Processing (2 edition)

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