Buazzi M M, Johnson M E, Marth E H
Department of Food Science, University of Wisconsin-Madison 53706.
J Dairy Sci. 1992 Feb;75(2):380-6. doi: 10.3168/jds.S0022-0302(92)77772-8.
Rindless Swiss cheese was made from a mixture of pasteurized whole and skim milk that was inoculated to contain 10(4) to 10(5) cfu of Listeria monocytogenes (strain Ohio, California, or V7)/ml. During clotting of milk, numbers of L. monocytogenes remained nearly unchanged. When the curd was heated gradually to attain the cooking temperature (50 degrees C), numbers of L. monocytogenes increased by approximately 40 to 45% over those in inoculated milk. Cooking curd at 50 degrees C (122 degrees F) for 30 to 40 min resulted in resilient curd having a pH of 6.40 to 6.45 and decreased L. monocytogenes by 48% compared with numbers of the pathogen in inoculated milk. After curd was pressed under whey, numbers of L. monocytogenes increased by approximately 52% over those in inoculated milk and reached their maxima at the end of this stage. A sharp decrease in numbers of L. monocytogenes occurred during brining of cheese blocks (7 degrees C for 30 h). The population of L. monocytogenes continued to decrease during cheese ripening. Average D values for strains California, Ohio, and V7 were 29.2, 24, and 22.5 d, respectively. Listeria was not detected (direct plating, and cold enrichment) after 80, 77, and 66 d of ripening of Swiss cheese made from milk inoculated with strains California, Ohio, and V7, respectively. Thus, Swiss cheese made in this study did not permit extended survival of L. monocytogenes.
无外皮瑞士奶酪由巴氏杀菌全脂牛奶和脱脂牛奶的混合物制成，接种后每毫升含有10⁴至10⁵cfu的单核细胞增生李斯特菌（俄亥俄州、加利福尼亚州或V7菌株）。在牛奶凝固过程中，单核细胞增生李斯特菌的数量几乎保持不变。当凝乳逐渐加热至烹饪温度（50℃）时，单核细胞增生李斯特菌的数量比接种牛奶中的数量增加了约40%至45%。在50℃（122℉）下将凝乳煮30至40分钟，得到的弹性凝乳pH值为6.40至6.45，与接种牛奶中病原体数量相比，单核细胞增生李斯特菌数量减少了48%。凝乳在乳清下压制成型后，单核细胞增生李斯特菌的数量比接种牛奶中的数量增加了约52%，并在这一阶段结束时达到最大值。在奶酪块腌制过程中（7℃，30小时），单核细胞增生李斯特菌数量急剧下降。在奶酪成熟过程中，单核细胞增生李斯特菌的数量持续减少。加利福尼亚州、俄亥俄州和V7菌株的平均D值分别为29.2、24和22.5天。分别用加利福尼亚州、俄亥俄州和V7菌株接种牛奶制成的瑞士奶酪，在成熟80、77和66天后未检测到李斯特菌（直接平板计数和冷增菌）。因此，本研究中制作的瑞士奶酪不允许单核细胞增生李斯特菌长期存活。
