To determine the effects of light exposure on vitamin A degradation and on light-oxidized flavor development, samples of whole, reduced fat, and nonfat milk were exposed to fluorescent light (either 1000 or 2000 lx) at time intervals of 2, 4, 8, or 16 h. Measurable vitamin A losses occurred at 2, 4, and 16 h at 2000 lx for nonfat, reduced fat and whole milk, respectively. Moderate light-oxidized flavors were detected after 4 h of light exposure (2000 lx) in the whole and reduced fat milk and after 8 h in nonfat milk. The different types of milk show a significant difference in relative flavor scores. By 16 h at 2000 lx, relative light-oxidized flavor development was lower in nonfat milk than in whole or reduced fat milk. The presence of milk fat appears to protect against vitamin A degradation in fluid products, but adversely affects the flavor quality of milk after exposure to light. In summary, these findings demonstrate that even a brief, moderate light exposure (2 h; 2000 lx) can reduce the nutritional value and flavor quality of fluid milk products.

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Reduced fat (2%) milk in high-density polyethylene (HDPE) containers was exposed to fluorescent light in a 6 °C walk-in cooler. Samples were evaluated by 10 trained panelists and by 94 consumers to assess the presence and intensity of sensory differences from unexposed control samples using the semi-ascending paired difference method. Trained panelists detected flavor defects following 15 to 30 min of light exposure; consumers detected defects between 54 min and 2 h. As approximately 50% of plastic containers remain in dairy cases for at least 8 h, these results suggest that the majority of milk on the market in light-transmissible containers is vulnerable to development of detectable light-oxidized flavor defects.

Current US regulations, as specified in the Pasteurized Milk Ordinance, require vitamin A fortification of all reduced fat fluid milk products. The addition of vitamin D is optional in all fluid products. Acceptable vitamin concentrations in fortified milks are 2000 to 3000 International units per quart for vitamin A and 400 to 600 International units per quart for vitamin D. Vitamin A and D levels were analyzed in fortified milk products collected over a 4-yr period in New York State. Samples of whole fat, 2% fat, 1% fat, and nonfat milks were collected twice per year from up to 31 dairy processing plants. For vitamin A, 44.5% of 516 samples were in compliance with current regulations, and 47.7% of 648 samples were within the acceptable range for vitamin D. Most milk samples that were out of compliance were underfortified.