The Effect of Light on Activated Flavor Development and on the Constituents of Milk and its Products: A Review

Abstract

Light from either natural or artificial sources causes chemical change (s) in a minor whey protein constituent of milk. These changes give rise to the development of an off-flavor commonly described as the activated flavor.Homogenized milk is more susceptible to this defect than is unhomogenized milk. It is believed that the increased area of protein surface adsorbed on the fat globules accounts for this greater susceptibility.The activated flavor may be detected in milk in clear glass bottles after exposure to sunlight for as little as 10 minutes. Prolonged exposure (1 to 2 hours) tends to decrease the intensity of the flavor. This phenomenon apparently is due to the further oxidation of the flavor compounds to flavorless components.The development of activated flavor may be retarded by the exclusion of air from milk. The flavor may be prevented by the addition of combinations of synergists and antioxidants, such as ascorbic acid and nordihydroguaiaretic acid.Containers made of ruby or amber glass or paper offer actinic protection to milk.There is no correlation between heat treatment, salt balance, breed, fat content,or stage of lactation and the susceptibility of milk to activated flavor development. The flavor develops more readily in milk produced by cows on dry feed than in that of cows on green feed. Milk from some cows seems to be more susceptible to activated flavor development than is the milk from other cows.Irradiation of milk to produce 135 to 400 U.S.P. units of vitamin D per quart does not cause appreciable loss of photosensitive vitamins. Prolonged exposure to natural or artificial light, however, may cause destruction of carotene, vitamins A and D, as well as thiamin, riboflavin, pyridoxine, ascorbic acid, and tocopherol in milk and its products. © 1953, American Dairy Science Association. All rights reserved.