Schaack Michelle M, Marth Elmer H
Department of Food Science and The Food Research Institute, University of Wisconsin Madison, Madison, Wisconsin 53706.
J Food Prot. 1988 Nov;51(11):848-852. doi: 10.4315/0362-028X-51.11.848.
Skim milks containing Listeria monocytogenes were fermented at 21, 30, 37 or 42°C for 15 h with Streptococcus lactis , S. cremoris , S. thermophilus , Lactobacillus bulgaricus or L. bulgaricus plus S. thermophilus (LBST). Amounts of inocula were 5.0, 1.0, 0.5 or 0.1%. Yogurt mix was inoculated with L. monocytogenes and fermented at 45°C for 5 h. Cultured skim milks and yogurt were stored at 4°C and sampled weekly to monitor survival of L. monocytogenes and the pH. Yogurt was sampled ca. every 3 d for enumeration of L. monocytogenes and determination of pH. Results show that L. monocytogenes survived longest in skim milks fermented with S. thermophilus , ranging from 4 weeks in skim milk fermented at 42°C with a 5.0% inoculum (final pH 4.62) to 37 weeks in skim milk fermented at 37°C with a 1.0% inoculum (final pH 4.52). When skim milks were fermented with S. lactis , L. monocytogenes survived from 2 weeks (5.0% inoculum, 30°C incubation, final pH 4.20) to more than 13 weeks (0.1% inoculum, 21°C incubation, final pH 4.70). L. monocytogenes survived from 4 (final pH 4.36) to 13 (final pH 5.30) weeks in milk fermented with S. cremoris . L. bulgaricus was the most detrimental to L. monocytogenes ; the pathogen survived only 3 d to 1 week in the skim milk fermented at 37°C with 0.1 % inoculum. Survival of L. monocytogenes in milk fermented with LBST culture ranged from 1 (final pH 3.93) to 12 (final pH 4.41) weeks in those skim milks in which the organism survived the fermentation process. L. monocytogenes survived yogurt manufacture and from 1 (final pH 4.13) to 12 (final pH 3.93) d during refrigerated storage of the product.
将含有单核细胞增生李斯特菌的脱脂乳分别与乳酸链球菌、嗜热链球菌、保加利亚乳杆菌或保加利亚乳杆菌加嗜热链球菌（LBST）在21、30、37或42℃下发酵15小时。接种量分别为5.0%、1.0%、0.5%或0.1%。将酸奶混合物接种单核细胞增生李斯特菌并在45℃下发酵5小时。将培养的脱脂乳和酸奶储存在4℃，每周取样以监测单核细胞增生李斯特菌的存活情况和pH值。酸奶大约每3天取样一次，用于单核细胞增生李斯特菌的计数和pH值的测定。结果表明，单核细胞增生李斯特菌在嗜热链球菌发酵的脱脂乳中存活时间最长，在42℃下用5.0%接种量发酵的脱脂乳中存活4周（最终pH值4.62），在37℃下用1.0%接种量发酵的脱脂乳中存活37周（最终pH值4.52）。当脱脂乳用乳酸链球菌发酵时，单核细胞增生李斯特菌存活时间从2周（5.0%接种量，30℃培养，最终pH值4.20）到超过13周（0.1%接种量，21℃培养，最终pH值4.70）。单核细胞增生李斯特菌在乳脂链球菌发酵的牛奶中存活4周（最终pH值4.36）至13周（最终pH值5.30）。保加利亚乳杆菌对单核细胞增生李斯特菌最具杀伤力；该病原体在37℃下用0.1%接种量发酵的脱脂乳中仅存活3天至1周。在LBST培养物发酵的牛奶中，单核细胞增生李斯特菌在那些在发酵过程中存活下来的脱脂乳中的存活时间为1周（最终pH值3.93）至12周（最终pH值4.41）。单核细胞增生李斯特菌在酸奶制作过程中存活下来，并在产品冷藏储存期间存活1天（最终pH值4.13）至12天（最终pH值3.93）。
