Dialysis Phosphatase Method for Milk and All Dairy Products

Abstract

Summary The principles, directions, and comparative results of a new phosphatase method for milk and milk products are presented. Dialysis through cellulose membranes, leading to a rapid separation of phenol accumulating in the cellulose bag from phosphatase activity, is the basis of the method. The separation occurs without attendant problems of protein interference or turbidity when color is developed with 2,6-dichloroquinone-chloroimide (CQC) in the receiving aqueous solution. Specifically, 5ml milk or 1g cheese are added to 10ml concentrated carbonate-bicarbonate buffer substrate residing in a small, single-service, knotted cellulose bag. The bag is incubated for 1 hr at 37C in 10ml of diluted copper-sulfate solution, after which it is removed and discarded. Two drops CQC are added to the clear liquid remaining and color permitted to develop for 5min. Phenol concentration is determined at this point, to complete the analysis. The Dialysis Phosphatase Test requires few reagents and its operation is basically simple. Comparative results between four laboratories, on standard fluid milk and Cheddar cheese samples, show good reproduction and indicate detection of less than 0.1% raw milk addition or a reduction of 1-2F in high-temperature—short-time pasteurization is readily possible.