Department of Food Science, Cornell University, Ithaca, New York 14853, USA.
J Food Prot. 2012 Sep;75(9):1619-26. doi: 10.4315/0362-028X.JFP-11-561.
The presence of the foodborne pathogen Listeria monocytogenes on cold-smoked salmon is a major concern for the seafood industry. Understanding processing and postprocessing handling factors that affect the ability of this pathogen to grow on cold-smoked salmon is critical for developing effective control strategies. In this study, we investigated the effect of curing method and freeze-thawing of cold-smoked salmon on (i) physicochemical properties and (ii) subsequent growth of genetically diverse strains of L. monocytogenes (inoculated after freeze-thawing) and endogenous lactic acid bacteria. The majority of the measured physicochemical properties were unaffected by freezing and thawing. Overall, wet-cured cold-smoked salmon had higher pH, water activity, and moisture, as well as lower fat, water-phase salt, and phenolic content compared with dry-cured cold-smoked salmon. The curing method and freeze-thawing did not affect growth of endogenous lactic acid bacteria. Freeze-thawing cold-smoked salmon prior to inoculation led to pronounced growth of L. monocytogenes at 7°C. The increase in cell density between days 0 and 30 was significantly (P = 0.0078) greater for cold-smoked salmon that was frozen and thawed prior to inoculation compared with nonfrozen cold-smoked salmon. On dry-cured, freeze-thawed cold-smoked salmon, L. monocytogenes had a lag phase ranging from 3.7 ± 0.1 to 11.2 ± 1.4 days compared with salmon that was wet cured and freeze-thawed, on which L. monocytogenes began to grow within 24 h. Variation in growth among L. monocytogenes strains was also observed, indicating the significance of assessing multiple strains. Further efforts to understand the impact of processing and postprocessing handling steps of cold-smoked salmon on the growth of genetically diverse L. monocytogenes will contribute to improved challenge study designs and data. This, in turn, will likely lead to more reliable and unbiased risk assessments and control measures.
食源性病原体单核细胞增生李斯特菌存在于冷熏三文鱼中，这是海鲜行业的主要关注点。了解影响该病原体在冷熏三文鱼上生长能力的加工和加工后处理因素对于制定有效的控制策略至关重要。在这项研究中，我们调查了腌制方法和冷熏三文鱼的冻融对（i）理化特性和（ii）随后（冻融后接种）遗传多样性单核细胞增生李斯特菌和内源性乳酸菌生长的影响。大多数测量的理化特性不受冷冻和解冻的影响。总体而言，湿腌冷熏三文鱼的 pH 值、水活度和水分较高，而脂肪、水相盐和酚类含量较低，与干腌冷熏三文鱼相比。腌制方法和冻融处理不会影响内源性乳酸菌的生长。在接种前将冷熏三文鱼冻融会导致 7°C 时单核细胞增生李斯特菌的明显生长。与未冷冻的冷熏三文鱼相比，接种前冻融冷熏三文鱼的细胞密度在 0 至 30 天之间的增加显著更大（P = 0.0078）。与湿腌和冻融的三文鱼相比，在干腌和冻融的三文鱼上，单核细胞增生李斯特菌的滞后期范围为 3.7 ± 0.1 至 11.2 ± 1.4 天，而单核细胞增生李斯特菌在湿腌和冻融的三文鱼上开始生长仅需 24 小时。还观察到单核细胞增生李斯特菌菌株之间的生长差异，表明评估多个菌株的重要性。进一步努力了解冷熏三文鱼加工和加工后处理步骤对遗传多样性单核细胞增生李斯特菌生长的影响将有助于改进挑战研究设计和数据。这反过来又可能导致更可靠和无偏的风险评估和控制措施。
