Activities and thermal stability of indigenous enzymes in cream and ice-cream mix

The activity and thermal stability of five indigenous enzymes viz., alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (GGTP), lactoperoxidase (LPO), N-acetyl-beta-glucosaminidase (NAGase), and xanthine oxidase (XO) in cream (20% and 40% fat levels) and ice-cream mix have been reported. Activities of ALP, NAGase and XO were significantly higher in 40% cream compared to 20% cream sample indicating that these enzymes are more abundant in cream phase. There was no significant difference in activities of GGTP and LPO enzymes in 40% and 20% cream samples. Although activities of ALP, GGTP, LPO and NAGase in ice-cream mix were lower or similar to cream samples, XO in ice-cream mix was higher than cream samples. The thermal stability of these enzymes was measured by calculating temperature (heat treatment for 15 s) required for 50% inactivation. Thermal stability of ALP was distinctly lower than other four enzymes. In 40% cream samples, the stability of enzymes was in order of XO > (LPO, GGTP)> NAGase>ALP. Except NAGase in ice-cream mix, all enzymes in cream and ice-cream mix were completely inactivated at 90 degrees C/15 s. Heat inactivated GGTP and LPO enzymes in 40% cream and ice-cream mix did not get reactivated during storage at -20, 5, and 20 degrees C. LPO and GGTP activities in cream and ice-cream mix can be used as indicator of heat treatment given to these products.