Thermal and Carbon Dioxide Inactivation of Alkaline Phosphatase in Buffer and Milk

Sibel Fadıloğlu*, Osman Erkmen and Gülten Şekeroğwlu

University of Gaziantep, Faculty of Engineering, Food Engineering Department, TR-27310 Gaziantep, Turkey

Article history:
Received: November 23, 2003
Accepted: February 16, 2004

Key words:
alkaline phosphatase, inactivation, milk, thermal stability

Summary:
The effects of temperature and CO₂ treatment on the inactivation of alkaline phosphatase (ALP) were studied. The thermal stability of ALP was found to be significantly (P< 0.05) different in glycine/NaOH buffer, pasteurized milk and raw milk. ALP was completely inactivated in the buffer at 60, 70 and 80 °C but approximately 12 % of activity was present at 50 °C after 55 min of treatment. The time required for complete inactivation of the enzyme in the buffer was reduced from 50 to 4 min as temperature increased from 60 to 80 °C. Complete inactivation of the enzyme in pasteurized milk was achieved at 70 and 80 °C but 28 and 15 % of ALP activity was still present at 50 and 60 °C after 120 min of treatment. Inactivation time for raw milk was reduced nearly 18-fold by increasing temperature from 50 to 70 °C. ALP in the buffer exposed to CO₂ (under atmospheric pressure) treatment at different temperatures showed a decrease in enzyme activity. Inactivation was found to be higher as the temperature increased from 20 to 50 °C. At the end of a 30-min treatment, residual ALP activity was found to be 84 and 19 % at 20 and 50 °C, respectively. Faster drop in pH and enzyme activity occurred within 5 min. The change in pH and enzyme activity dependant on CO₂ treatment was not observed in raw milk mainly due to strong buffering capacity of milk. 

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