A rancid flavor to milk can have a serious impact on consumers.
Milk with rancid flavor is soapy or bitter. This characteristic odor of rancid milk is derived from the unpleasant volatile fatty acids that formed as the result of lipid hydrolysis. It caused by the chemical cleavage of short chain fatty acids from triglycerides.
Lipase activity that forms free fatty acids from milk fat continues to occurs until milk is pasteurized.
Intact protein membranes normally encapsulate milk fat molecules and protect the fat from enzyme activity. Short chain fatty acids – butyric, caproic, caprylic, lauric and capric acids in the sn1 and sn3 positions of the triacyl-glycerols are particular susceptible to hydrolysis by lipase.
Rancidity is produced by hydrolysis of the fatty acid from the glycerol backbone of the triglyceride.
Triglycerides are structurally similar in all edible fats and oils.
Triglycerides of milk fat are unique because they contain a group of fatty acids that are small enough when free to be volatile and odorous.
Milk rancidity
