Inactivation and Reactivation of Xanthine Oxidase in Dairy Products

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Abstract
The effect of pasteurization, condensation, homogenization and drying on xanthine oxidase (XO) has been studied. Heating whole milk to 195[degree] F for 15 sec. inactivates the XO; but when the milk is condensed to 50% total solids and homogenized at 4,500 psi, a portion of the XO is reactivated. More than 94% of the XO is inactivated when milk is exposed to sonic vibrations of a frequency of 10,000 vibrations/sec. for 7-1/2 hr. The effect of mechanical stress on XO activity during processing of dairy products is discussed. XO activity may be used to estimate the heat treatment a milk powder has received in processing.