Determination of Xanthine Oxidase in Milk with Triphenyl Tetrazolium Chloride

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Abstract
A method is described for determination of xanthine oxidase in milk with triphenyl tetrazolium chloride. The enzymatic reaction is performed with nitrogen gas bubbling through the mixture to avoid oxygen which is inhibitory. Subsequent steps, which include color extraction with toluene after acidification with acetic acid, are performed in air since the red, reduced form of triphenyl tetrazolium chloride is stable. The effects of concentration of substrate and triphenyl tetrazolium, and other factors are investigated. The method is used to show the destruction of xanthine oxidase in skim milk at 55 to 75[degree]C.