The Effect of Heat Treatment on the Sulfhydryl Groups in Skimmilk and Nonfat Dry Milk

Summary The sulfhydryl groups in milk proteins have been determined by the amperometric-argentometric method of Kolthoff. All or almost all the -SH groups in milk are present in the whey proteins. Heating milk causes an initial small rise in titrable -SH groups, followed by a marked decrease in -SH. The temperature at which the first sharp decrease in -SH groups is seen has been called the “critical temperature.” There is an apparent relation between the “critical temperature” and the appearance of cooked flavor. The loss of -SH groups found on heating milk above its “critical temperature” is a first order reaction. Heating in the presence or absence of dissolved oxygen or in the presence of oxidizing agents does not affect the value of the “critical temperature.” The method of Kolthoff is recommended as a useful tool for the evaluation of the effects of heat treatment on milk and milk products.