Volatile Sulfur Compounds in Milk. I. Effect of Chemical Form of 35S on Selective Labeling of Milk Constituents and Free Sulfur Compounds

Abstract

The use of different chemical forms of 35S provided a means of obtaining radioactive milk with varying specific radioactivity of the sulfur in the protein and nonprotein sulfur components. Preferential labeling of milk proteins was obtained with methionine-35S, Na235S, and Ba35S, whereas preferential labeling of nonprotein sulfur was obtained with Na235SO4. When Ba35S was used, equal specific activity was found in both the casein and whey protein fractions.Low concentrations (parts per billion) of hydrogen sulfide, mercaptans, organic sulfides, and carbonyl-35S compounds were found in unheated raw milk. The type and concentration of free volatile sulfur compounds varied with the type of sulfur compound used or with the individual cow, or both. Generally, higher concentrations of free organic sulfides were found in skimmilk, cream, and rennet whey than in the original milk. Skimmilk and acid whey contained higher concentrations of free mercaptans, and buttermilk contained three times more hydrogen sulfide than the original milk.