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The Origin of Sulfhydryl Groups in Milk Proteins and their Contributions to "Cooked" Flavor¹

Department of Dairy Husbandry, The Pennsylvania Agricultural Experiment Station, State College

ABSTRACT

Use of an argentometric-amperometric titration procedure has revealed that the only source of -SH groups in skimmilk is the serum proteins. Casein and protein-free milk serum were found devoid of such groups. Praetionation of the serum protein material into a number of components by (NH₄)₂ S0₄ additions and pH adjustments revealed that ß-lactoglobulin can account for practically all the -SH groups present. Study of the contributions of various major serum protein fractions to heat-induced cooked flavor in skimmilk demonstrated ßlacto-globulin to be responsible for the flavor. Conversion of -SH groups to H₂S as a result of heat treatment may explain, in a general way, the mechanism whereby ß-lactoglobulin gives rise to cooked flavor.

The AgNO₃ titration, when conducted in aqueous medium, appears to measure the same quantity of -SH groups in heated milk as nitroprusside and thiamin disulfide. When conducted in alcoholic medium the total number of -SH groups capable of activation by heat treatment presumably can be determined in unheated skimmilk. The argentometric-amperometric method gives values for -SH content of slightly less than half of those obtained with o-iodosobenzoate for both skimmilk and ß-lactoglobulin.

¹ Authorized for publication March 31, 1952 as paper no. 1727 in the Journal Series of the Pennsylvania Agricultural Experiment Station.

² Present address: Golden State Co., Ltd., San Francisco, Calif.

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