The influence of heat and vacuum treatment on the rancid flavor of milk

The dairy industry strives to serve the public with a safe wholesome milk supply which has an acceptable, standardized flavor. Off-flavors and odors in milk may be caused by feeds eaten by the cow, absorption of odors and flavors by the milk, and development of flavors and odors during processing and handling. Rancid flavor may be caused by improper handling or processing which may activate the lipase system of milk. The short chain fatty acid content of the milk, which is responsible for the rancid flavor, is increased due to the hydrolysis of the milk fat by the lipase system. Some of the newer methods of handling milk have been found to activate the lipase system. The result is that much of the milk is on the threshold of being detectably rancid when it reaches the processing plant. Vacuum treatments with or without steam injection have been effective in the removal of volatile compounds which cause many off-flavors in milk. These treatments are widely used in standardizing the flavor of milk during seasons of the year when feed flavors are generally a problem for the dairy industry. Likewise, in steam refining of edible oils, a vacuum steam distillation process, the low molecular weight fatty acids are largely removed. During this process the distillate, generally less than 0,5 per cent of the total product, is removed. The purpose of this investigation was to determine if a vacuum treatment, in which a distillate is removed and replaced by water, could remove the flavor caused by hydrolytic rancidity from milk.