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


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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