Inactivation and Reactivation of Xanthine Oxidase in Dairy Products

Abstract

The effect of pasteurization, condensation, homogenization, and drying on xanthine oxidase (XO) has been studied. It has been found that heating whole milk to 195 F for 15 sec inactivates the XO, but when the same 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 per second for 7½ hr. The effect of mechanical stress applied to milk during processing on XO activity in dairy products is discussed. Data are presented which indicate that XO activity may be used to estimate the heat treatment a milk powder has received in processing. © 1962, American Dairy Science Association. All rights reserved.