Effect of Changes in Sulfur Compounds on Stability and Gelation of Caseins and of Sterile Concentrated Milk

Strong disulfide reducing agents Na~SQ and NaBH~ increased nonprotein nitrogen (NPN) in the casein complex from sterile concentrated milk. The sulfur-containing reducing agents mercaptoethanol, thioglycolate, and eysteine reduced the disulfide linkages and decreased stabilities to Ca" of the casein complex, of whole and of K-easeins with slight changes in NPN. Increasing pH to 12 with 0.1 h" Na0H also split the linkages and decreased stability of whole and K-caseins. Decreased stabilities were ahnost completely restored by air oxidation and neutralization. Degrading ~-and whole caseins with Na0H and NaBH, doubled the sulfur eompounds by the p-mercuribenzoate (PMB) method as compared to reducing them with Na~SO.~.