Determination of Sulfhydryl Groups in Milk Using Ellman's Procedure and Clarifying Reagent®

This work reports on a rapid method for determination of total sulfhydryl groups in raw and heated milks using 5,5'-dithio-bis(2-nitrobenzoic acid). The reaction medium is clarified after the chemical reaction by addition of a dissolving agent; thus, the spectrophotometric measurements are performed directly in milk without other sample treatment. This protocol correlated well with amperometric titrations (r=.994). Results on raw milks from individual cows showed seasonal variations in sulfhydryl groups. Sulfhydryl groups decreased in heated commercial milks. This method is simple, rapid, and easily applicable in routine measurements and may allow heated commercial milks to be distinguished.