Pearson Laura J, Marth Elmer H
Department of Food Science and The Food Research Institute, University of Wisconsin-Madison, Madison, Wisconsin 53706.
J Food Prot. 1990 Jan;53(1):47-50. doi: 10.4315/0362-028X-53.1.47.
Two components of cocoa powder, caffeine (1,3,7-trimethylxanthine) and theobromine (3,7-dimethylxanthine), were evaluated for their effect on growth of L. monocytogenes strain V7. Caffeine (0.5%) and theobromine (2.5%) were added singly or in combination to skim milk or a modified tryptose phosphate broth (MTPB), which were sterilized, inoculated to contain ca. 1 × 10 CFU L. monocytogenes /ml, and incubated at 30°C. Both compounds allowed some growth of the pathogen; however, longer lag phases occurred in samples with (6 to 9 h) rather than without (<3 h) caffeine. Generation times at 30°C ranged from 1.10 h (2.5% theobromine in broth) to 2.28 h (2.5% theobromine plus 0.5% caffeine in milk). Generation times were significantly (p<0.05) lengthened in the presence (2.17 h) rather than in the absence (1.2 h) of caffeine. Populations in samples without caffeine were more than ten times greater (8.57 log CFU/ml) than in samples with caffeine (7.21 log CFU/ml). Theobromine concentration (0 or 2.5%) and substrate (MTPB or skim milk) had only limited effects on growth of the pathogen. The change in pH of the medium was a function of the extent of growth of L. monocytogenes and the buffering capacity of the substrate. A smaller pH change (0.09 unit) occurred in the milk medium than in broth (0.48 unit) because of the minimal buffering capacity of the 0.2% tryptose solution. Samples with caffeine had a small decrease in pH (0.07 unit) because growth of L. monocytogenes was inhibited and thus acid production was minimal.
对可可粉的两种成分咖啡因（1,3,7 - 三甲基黄嘌呤）和可可碱（3,7 - 二甲基黄嘌呤）对单核细胞增生李斯特菌V7菌株生长的影响进行了评估。将咖啡因（0.5%）和可可碱（2.5%）单独或联合添加到脱脂牛奶或改良胰蛋白胨磷酸盐肉汤（MTPB）中，进行灭菌处理，接种使其含有约1×10⁵CFU/毫升的单核细胞增生李斯特菌，然后在30℃下培养。两种化合物都使病原体有一定程度的生长；然而，含有咖啡因的样品（6至9小时）比不含咖啡因的样品（<3小时）出现更长的迟缓期。在30℃下的代时范围为1.10小时（肉汤中2.5%的可可碱）至2.28小时（牛奶中2.5%的可可碱加0.5%的咖啡因）。在有咖啡因存在时（2.17小时），代时显著延长（p<0.05），而在无咖啡因时（1.2小时）则不然。不含咖啡因的样品中的菌数（8.57 log CFU/毫升）比含咖啡因的样品（7.21 log CFU/毫升）多十倍以上。可可碱浓度（0或2.5%）和底物（MTPB或脱脂牛奶）对病原体生长的影响有限。培养基pH值的变化是单核细胞增生李斯特菌生长程度和底物缓冲能力的函数。由于0.2%胰蛋白胨溶液的缓冲能力最小，牛奶培养基中的pH变化较小（0.09个单位），而肉汤中的pH变化较大（0.48个单位）。含有咖啡因的样品pH略有下降（0.07个单位），因为单核细胞增生李斯特菌的生长受到抑制，因此产酸量极少。
