Whited L J, Hammond B H, Chapman K W, Boor K J
Department of Food Science, Cornell University, Ithaca, NY 14853, USA.
J Dairy Sci. 2002 Feb;85(2):351-4. doi: 10.3168/jds.S0022-0302(02)74080-0.
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.
为了确定光照对维生素A降解以及光氧化风味形成的影响，将全脂、低脂和脱脂牛奶样品分别以2、4、8或16小时的时间间隔暴露于荧光灯下（光照强度为1000或2000勒克斯）。在2000勒克斯光照下，脱脂、低脂和全脂牛奶分别在2小时、4小时和16小时出现了可测量的维生素A损失。在全脂和低脂牛奶中，光照4小时（2000勒克斯）后检测到中度光氧化风味，在脱脂牛奶中光照8小时后检测到中度光氧化风味。不同类型的牛奶在相对风味评分上存在显著差异。在2000勒克斯光照16小时后，脱脂牛奶中相对光氧化风味的形成低于全脂或低脂牛奶。乳脂肪的存在似乎能防止液态产品中维生素A的降解，但在光照后会对牛奶的风味质量产生不利影响。总之，这些研究结果表明，即使是短暂的中度光照（2小时；2000勒克斯）也会降低液态奶制品的营养价值和风味质量。
