Ryser E T, Marth E H
Department of Food Science, University of Wisconsin-Madison 53706.
Can J Microbiol. 1988 Jun;34(6):730-4. doi: 10.1139/m88-124.
Wheys from making Camembert cheese were either uncultured or cultured with Penicillium camemberti, adjusted to pH 5.0, 5.2, 5.4, 5.6, 6.2, and 6.8, and filter sterilized. Whey samples were inoculated to contain 100 to 500 Listeria monocytogenes (strains Scott A, V7, CA, or OH) cfu/mL and incubated at 6 degrees C. Counts of L. monocytogenes were obtained by surface plating appropriate dilutions on Tryptose Agar. Listeria monocytogenes failed to grow at or below pH 5.4; except for strains Scott A and OH which grew in cultured whey at pH 5.4 and attained populations of 7.8 x 10(3) and 5.4 x 10(4) cfu/mL, respectively, after 35 d of storage. In uncultured whey at pH 5.6, 6.2, and 6.8, populations of L. monocytogenes increased from 7.20 to 7.81, 7.51 to 8.23, and 7.48 to 8.08 log10 cfu/mL, respectively, after 35 d of storage at 6 degrees C. In cultured whey at pH 5.6, 6.2, and 6.8, numbers of L. monocytogenes increased from 7.53 to 8.13, 7.82 to 8.55, and 7.95 to 8.80 log10 cfu/mL, respectively, after 35 d of storage. Generation times for L. monocytogenes at 6 degrees C in uncultured whey at pH 5.6, 6.2, and 6.8 ranged between 25.3 and 31.6 h, 14.8 and 21.1 h, and 14.0 and 19.4 h, respectively, depending on the Listeria strain. In contrast, generation times were significantly (p less than 0.05) shorter in cultured whey and ranged between 16.6 and 27.4 h, 10.3 and 16.6 h, and 17.4 and 16.3 h at pH values of 5.6, 6.2, and 6.8, respectively.
制作卡门培尔奶酪产生的乳清，一部分未经培养，另一部分用卡门培尔青霉进行培养，将其pH值分别调至5.0、5.2、5.4、5.6、6.2和6.8，然后进行过滤除菌。向乳清样品中接种单核细胞增生李斯特菌（菌株Scott A、V7、CA或OH），使其浓度达到100至500 cfu/mL，并在6℃下培养。通过将适当稀释度的样品表面接种于胰蛋白胨琼脂平板来计数单核细胞增生李斯特菌。单核细胞增生李斯特菌在pH值5.4及以下无法生长；不过，菌株Scott A和OH在pH值为5.4的培养乳清中能够生长，储存35天后，菌量分别达到7.8×10³ cfu/mL和5.4×10⁴ cfu/mL。在pH值为5.6、6.2和6.8的未培养乳清中，于6℃储存35天后，单核细胞增生李斯特菌的菌量分别从7.20 log₁₀ cfu/mL增加至7.81 log₁₀ cfu/mL、从7.51 log₁₀ cfu/mL增加至8.23 log₁₀ cfu/mL、从7.48 log₁₀ cfu/mL增加至8.08 log₁₀ cfu/mL。在pH值为5.6、6.2和6.8的培养乳清中，储存35天后，单核细胞增生李斯特菌的数量分别从7.53 log₁₀ cfu/mL增加至8.13 log₁₀ cfu/mL、从7.82 log₁₀ cfu/mL增加至8.55 log₁₀ cfu/mL、从7.95 log₁₀ cfu/mL增加至8.80 log₁₀ cfu/mL。在6℃下，单核细胞增生李斯特菌在pH值为5.6、6.2和6.8的未培养乳清中的代时分别介于25.3至31.6小时、14.8至21.1小时和14.0至19.4小时之间，具体取决于李斯特菌菌株。相比之下，在培养乳清中的代时显著缩短（p＜0.05），在pH值为5.6、6.2和6.8时，代时分别介于16.6至27.4小时、10.3至16.6小时和17.4至（此处原文有误，推测应为16.3至）16.3小时之间。
