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Dialysis Phosphatase Method for Milk and All Dairy Products

Department of Dairy and Food Science, Cornell University, Ithaca, New York

ABSTRACT

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, 5 ml milk or 1 g cheese are added to 10 ml concentrated carbonate-bicarbonate buffer substrate residing in a small, single-service, knotted cellulose bag. The bag is incubated for 1 hr at 37 C in 10 ml 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 5 min. 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 1-2 F in high-temperature—short-time pasteurization is readily possible.