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):38-46. doi: 10.4315/0362-028X-53.1.38.
Dutch-processed cocoa (0.75 to 10.0%, w/v), when added to a broth medium, inhibited/inactivated Listeria monocytogenes strain V7. With agitated incubation at 30°C, samples with 5.0, 7.5, and 10.0% cocoa were free of detectable viable cells (<1/ml) 15 to 24 h after inoculation to contain ca. 1 × 10 L. monocytogenes strain V7/ml. Without agitation at 30°C, presence of 0.75 to 10.0% cocoa lengthened (1.02 to 1.12 h) the generation time of the pathogen when compared to samples without cocoa (0.94 h). However, the pathogen, in samples containing cocoa, eventually reached a higher (9.05 to 9.18 log CFU/ml) population than in samples without cocoa (8.81 log CFU/ml). The lag phase of L. monocytogenes was longer with (8.15 h) rather than without (4.41 h) agitation, at a lower (ca 1×10 CFU/ml) (6.92 h) rather than a higher (ca. 1 × 10 CFU/ml) (5.65 h) inoculum level, and in the presence of 0.75% (10.52 h) rather than 0% (2.04 h) cocoa. Higher maximum populations (9.18 log CFU/ml) developed in samples that were agitated rather than incubated quiescently (8.39 log CFU/ml), and in samples with (9.23 log CFU/ml) rather than without (8.88 log CFU/ml) cocoa. Casein (1.5 or 3.0%) relieved the inhibition when incubation was quiescent and inactivation of L. monocytogenes by cocoa when incubation was with agitation. Without agitation, the lag phase of the pathogen was extended in the presence of cocoa (4.01 h) compared to samples with cocoa and casein (1.77 to 2.74 h). Casein did not significantly (p>0.05) affect the maximum population attained by the pathogen, but presence of cocoa increased the maximum population (8.86 and 9.25 log CFU/ml for 0 and 5.0% cocoa). With agitation, presence of 5.0% cocoa completely inactivated the pathogen; however, addition of 2.5% casein to these samples allowed growth of L. monocytogenes to a population of 9.47 log CFU/ml (compared to 8.90 log CFU/ml in broth).
荷兰加工可可（0.75%至10.0%，w/v）添加到肉汤培养基中时，可抑制/灭活单核细胞增生李斯特菌V7株。在30°C振荡培养条件下，接种约1×10⁵单核细胞增生李斯特菌V7株/ml后，含5.0%、7.5%和10.0%可可的样品在接种后15至24小时内未检测到存活细胞（<1/ml）。在30°C无振荡培养条件下，与不含可可的样品（代时0.94小时）相比，0.75%至10.0%可可的存在使该病原菌的代时延长（1.02至1.12小时）。然而，含可可样品中的病原菌最终达到的菌数（9.05至9.18 log CFU/ml）高于不含可可的样品（8.81 log CFU/ml）。在较低接种量（约1×10³CFU/ml，代时6.92小时）而非较高接种量（约1×10⁵CFU/ml，代时5.65小时）下，在有（8.15小时）而非无振荡（4.41小时）条件下，以及在有0.75%（10.52小时）而非0%（2.04小时）可可存在时，单核细胞增生李斯特菌的迟缓期更长。振荡培养的样品中病原菌达到的最大菌数更高（9.18 log CFU/ml），而非静置培养的样品（8.39 log CFU/ml），且含可可样品（9.23 log CFU/ml）而非不含可可的样品（8.88 log CFU/ml）中病原菌达到的最大菌数更高。在静置培养时，酪蛋白（1.5%或3.0%）可缓解可可对单核细胞增生李斯特菌的抑制作用，在振荡培养时可缓解可可对该菌的灭活作用。在无振荡条件下，与含可可和酪蛋白的样品（1.77至2.74小时）相比，可可存在时病原菌的迟缓期延长（4.01小时）。酪蛋白对病原菌达到的最大菌数无显著影响（p>0.05），但可可的存在增加了最大菌数（0%和5.0%可可时分别为8.86和9.25 log CFU/ml）。在振荡培养条件下，5.0%可可可完全灭活病原菌；然而，向这些样品中添加2.5%酪蛋白可使单核细胞增生李斯特菌生长至菌数为9.47 log CFU/ml（肉汤中为8.90 log CFU/ml）。
