A Sensitive Quantitative Assay for Milk Coagulants in Cheese and Whey Products

Abstract

The parameters of a sensitive quantitative assay have been explored and the assay utilized for the determination of milk coagulants in whey, cheese, and whey powder. Cheeses were extracted with sodium cacodylate-HCl buffer (pH 6.0) containing .86 M NaCl (5% wt/vol) and .1 M CaCl2. Cheese whey protein concentrate powders, reconstituted to 5% total solids, and whey samples were assayed directly. The basic method preincubates the test sample with dilute skim milk, and at measured time intervals, aliquots of the preincubated milk are mixed with known quantities of standard milk coagulant, and the change in clotting time as a function of preincubation time is determined. The decrease in coagulation time is proportional to the concentration of milk coagulant in the original test sample. The method is sensitive (1 × 10–4 rennet units/ml of lest sample), and the sensitivity could be further increased by modification of test parameters such as pH, temperature, and milk concentration. © 1990, American Dairy Science Association. All rights reserved.