Table 1 Characteristics of indigenous milk enzymes (Kitchen, 1985)

Enzyme		Distribution in milk	Specificity	Opt.pH	Opt.temp (℃)	Activity in bovine milk	Use or function	Mw
Hydrolase	Plasmin	Casein	Hydrolysis of peptide bonds on C-terminal sides of lysyl and arginyl residue β-casein > αs-casein > κ-casein	8.0	37		UHT milk gelling	48,000
	Acidprotease		Hydrolysis of peptide bonds optimally at acid pH αs-casein > β- and κ-casein	4.0			Cheese ripening	36,000
	Lipase	Casein (80%)	Orthophosphoric monoester	8.5~9.0	37	2 µmole/min.mL FFA	Hydrolytic rancidity	10,000
	Alkaline phosphatase	Membranestructure	Hydrolysis of phosphomonoester	9.8	37	500 µmole/min.mL	Pasteurization test	160,000~190,000
	Acid phosphatase	Serum membranestructure	Hydrolysis of mucopolypeptide	4.9			UHT milk gelling	42,000
	Lysozyme	Serum	Oxidation of sulfhydryl group	7.9	37	130 µg/L	Bactericide	14,600
Oxidase	Sulfhydryl oxidase	Serum	Dismutation of superoxide ion to H2O2 and O2	7.0∼8.0	45∼50	3 mg/L	Removal of burnt, cooked flavor	1,000,000
	Superoxidasedismutase	Skim milk	Oxidation of xanthine, hypoxanthine, aldehyde producing H2O2 and superoxide			0.1∼0.25 µmole/min.L	Oxidation deterrent	32,000
	Xanthine oxidase	Fat globule membrane	Transfer of oxygen from H2O2 to other substrate(suchas thiocyanate)	6.0∼9.0	37	175 µmole/min.L	Oxidation catalyst	275,000~300,000
	Lacto-peroxidase	Serum	Transfer of oxygen from H2O2 to other substrate (such as thiocyanate)	6.0∼7.0	20	22,000µmole/min.L	Bacterial destruction	77,500
	Catalase	Membranestructure	Decomposition of H2O2 to O2 and H2O	7.0		300µmole/min.L	Mastitis diagnosis	210,000
Transfe-rase	γ-Glutamyl transpeptidase	Membranestructure	Transfer of γ-glutamyl residues from substrate such as glutathione to an acceptor such another glutamyl residue, hydroxylamine, glycyglycine or water	9.0	45		Amino acid up take into mammary gland	80,000
	Galactosyl- transferase	Serum	Transfer of galactosyl residue from UDP-galactose to an N-acetylglucosamine either free or in a protein bound oligomer	7.2	37	50µmole/min.L	Lactose biosynthesis in mamary aland	42,000