Activity and thermal stability of indigenous enzymes in cow, buffalo and goat milk

Abstract

The activity and thermal stability of five indigenous milk enzymes viz., lactoperoxidase (LPO), N-acetyl-β-glucosaminidase (NAGase), γ-glutamyl transpeptidase (GGTP), alkaline phosphatase (ALP) and xanthine oxidase (XO) in cow, buffalo and goat milks have been reported. The activities of these enzymes in goat milk were significantly lower than in bovine or buffalo milks. There were large differences in activities of LPO amongst these milks. As compared to cow milk, buffalo milk exhibited nearly 1.76 fold higher activities while, goat milk contained nearly 8.87 fold lower activity. Goat milk showed nearly 4 fold lower NAGase and GGTP activities as compared to either cow or buffalo milk. There was no significant difference in activities of NAGase, GGTP, ALP and XO in milks from bovine and buffalo. It was observed that ALP and XO activities were concentrated in cream phase; LPO and NAGase activities were more in skim milk phase and GGTP activity distributed in both the phases. The thermal stability (15 s at different temperature ranging from 65°C to 90°C) varied from enzyme to enzyme. Thermal inactivation pattern of individual enzyme from bovine, buffalo and goat milks was similar. The thermal stability of these five enzymes was in order of XO > LPO > (GGTP, NAGase) > ALP. Measurement of these enzymes in processed milk can provide information on heat treatment subjected to milk.