Casein

Since writing this report, we found that the intravenous injection of nucleoprotein, casein, and probably also other albuminous substances may produce small necroses of liver tissue in the guinea pig. This observation points to a possible danger in the use of casein solutions."

It’s the clumping nature of the caseins that makes possible most thickened milk products, from yogurt to cheese. The whey proteins play a more minor role; they influence the texture of casein curds, and stabilize the milk foams on specialty coffees.