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Fluorometric Determination of Sulfhydryl and Disulfide Groups in Whey from Milk Processed by Turbulent Flow Ultra-High Temperature Processes

Department of Food Science and Technology and Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg 24061

ABSTRACT

Milk was processed in a helically coiled tube heat exchanger in increments of 5.5 C at holding temperatures of 65.6 to 148.9 C. The heating, holding, and cooling times of each process were 4.8, .18, and 1.85 s. The d~sulfide and sulfhydryl groups and proteins in rennet whey from raw and processed milk were quantified fluorometrically and electraphoretically. The mean of the groups in raw milk whey was 2.89 ± .26 µmoles/ml of which 1.94 µmoles were in the whey proteins. Processes at holding temperatures in the range of 65.6 to 82.2 C caused no significant decreases in the groups. In the range 82.2 to 148.9 C, percentage decreases were linear (correlation .96) and were closely related to percentage decreases in ß-lactoglobulin, indicating that fluorometric measurement of the groups in whey could be used as an index of heat treatment of milk. The regression of area in square centimeters of electrophoretic patterns of ß-lactoglobulin (Y) on µmoles of disulfide + sulfhydryl/ml of whey (X) was: Y = 4.48X – 7.1, correlation .97.

¹ Present address: Richard B. Russell Agricultural Research Center, USDA-ARS, Athens, Georgia 30604.