Effect of Light on Alteration of Nutritional Value and Flavor of Milk: A Review1

Abstract

Milk in glass, polycarbonate, high density polyethylene, blow-molded polyethylene, plastic bags and paperboard containers, when exposed to fluorescent light or sunlight, will develop a characteristic off-flavor described synonomously by many researchers as activated, sunlight or oxidized flavor. The extent of flavor development is related to the exposure interval, strength of the light and amount of milk surface exposed. Paperboard containers. particularly those with large printed areas of dark ink or foil in the laminate, offer the best protecton to milk, while the remaining containers offered limited protection at best. Characteristic flavor is produced prinicipally by conversion of methionine to methional. Partial loss of vitamins B2 and C and some amino acids parallel development of light-induced off-flavor. Loss of other constituents is minimal. Many researchers offered suggestions to improve the flavor stability of milk held in display cases illuminated with fluorescent lights. Among these are changes to more protective packaging, reduction of radiant energy to 538 lux, use of gold or “bug light” types of fluorescent lights and more dark ink areas on exposed parts of paperboard cartons (gables and main display panels). Perhaps grocers should bag all containers of milk to afford adequate protection from sunlight between points of refrigeration.