A Modified Phosphatase Test for Cheese

Abstract

Summary A phosphatase test for cheese is presented in detail with data showing its sensitivity. This method possesses a number of advantages. It is very accurate, as the final filtrates produced in this modification were clear and devoid of interfering substances. Conditions of incubation promote maximum phosphatase activity. The Folin-Ciocalteu color reagent and the BQC color reagent can be used interchangeably with proper color standards. Apparently, any natural or process cheese or cheese product can be tested without making adjustments in the buffer substrate or precipitating agent. In the new method the cheese sample is incubated with a sodium carbonate-bicarbonate buffer substrate at pH 9.55 for 18 to 24 hours at 32 to 37° C. This solution then is precipitated by a trichloracetic-hydrochloric acid reagent and some of the clear filtrate is placed in either a standard size or a small Mojonnier type extraction flask. Ethyl ether is used as the extracting agent but later is boiled off from an alkaline solution leaving the phenol behind. The phenol in this alkali solution then is determined colorimetrically by adding either the Folin-Ciocalteu or the BQC color reagent and comparing the developed blue colors against proper color standards. The sensitivity of this method is high. Tentatively, any value above 0.02 mg. phenol per 0.5 g. cheese, using the Folin-Ciocalteu reagent, or any value over 5.0 γ phenol per 0.5 g. cheese, using the BQC reagent, is considered to indicate cheese made from raw milk, improperly pasteurized milk or pasteurized milk contaminated with raw milk.