Milk Lipids: Lipid Oxidation

Abstract

Lipid oxidation involves the attack by molecular oxygen on unsaturated fat molecules. It is generally undesirable in food products including milk fats as it can give rise to undesirable volatile flavor compounds, potentially toxic oxidation products, and a general deterioration in the quality of the fat. Oxidation of unsaturated fats is typically an autocatalytic free-radical process involving initiation, propagation, and termination stages. It results in the formation of unstable intermediate fatty acid hydroperoxides which ultimately degrade to yield a wide range of volatile compounds contributing to rancidity of the fat. The rate and extent of lipid oxidation in milk and milk products is influenced by a range of parameters, including oxygen, light, endogenous and exogenous metals, antioxidants such as ascorbic acid, tocopherols, carotenoids, thiols, proteins, enzymes, and also by milk fat globule membrane components and storage temperature. Cholesterol in milk fat is also susceptible to oxidation giving rise to so-called cholesterol oxidation products (COPs). The health significance of COPs, particularly in relation to atherosclerosis, is a matter of ongoing research and debate. While COPs are not normally present at significant levels in milk and milk products, it is prudent to optimize processing parameters to minimize the formation of COPs.