Douglas S A, Gray M J, Crandall A D, Boor K J
Department of Food Science, Cornell University, Ithaca, New York 14853, USA.
J Food Prot. 2000 Apr;63(4):516-21. doi: 10.4315/0362-028x-63.4.516.
Standard plate counts (SPC) and psychrotrophic plate counts (PPC) from chocolate milk samples were compared with those of unflavored milk samples plated within 24 h of processing and at 7, 10, and 14 days of storage at 6 degrees C using matched samples collected over four time periods from four milk-processing plants. Bacterial numbers within 24 h of processing were not significantly different in unflavored and in chocolate milk samples (P > 0.001), with SPC less than 1,000 CFU/ml and PPC below 10 CFU/ml for both types of products. SPC and PPC were higher in chocolate milk samples than in unflavored milk samples collected from all four plants after 14 days of storage (P < 0.001). To examine the effects of chocolate milk components on bacterial numbers, SPC for days 0, 7, 14, and 21 were monitored in samples of experimentally prepared unflavored milk, milk with chocolate powder and sucrose (chocolate milk), milk with sucrose only, and milk containing chocolate powder only. At days 14 and 21, SPC were higher in both chocolate milk and in milk with chocolate powder only, than in either the unflavored milk or milk with sucrose only (P < 0.001). These findings suggest that the addition of chocolate powder to milk can contribute to a greater relative increase in bacterial numbers in pasteurized chocolate milk than in identically processed unflavored milk at 14 days postprocessing.
使用从四个牛奶加工厂在四个时间段收集的匹配样本，将巧克力牛奶样本的标准平板计数（SPC）和嗜冷菌平板计数（PPC）与加工后24小时内以及在6摄氏度下储存7天、10天和14天的原味牛奶样本的计数进行比较。加工后24小时内，原味牛奶和巧克力牛奶样本中的细菌数量没有显著差异（P>0.001），两种产品的SPC均低于1000 CFU/ml，PPC均低于10 CFU/ml。储存14天后，从所有四个工厂收集的巧克力牛奶样本中的SPC和PPC均高于原味牛奶样本（P<0.001）。为了研究巧克力牛奶成分对细菌数量的影响，对实验制备的原味牛奶、含有巧克力粉和蔗糖的牛奶（巧克力牛奶）、仅含蔗糖的牛奶以及仅含巧克力粉的牛奶样本在第0天、第7天、第14天和第21天的SPC进行了监测。在第14天和第21天，巧克力牛奶和仅含巧克力粉的牛奶中的SPC均高于原味牛奶或仅含蔗糖的牛奶（P<0.001）。这些发现表明，在加工后14天时，向牛奶中添加巧克力粉会使巴氏杀菌巧克力牛奶中的细菌数量相对增加幅度大于相同加工的原味牛奶。
