Canadian Research Institute for Food Safety, Department of Food Science, University of Guelph, Guelph, Ontario, Canada.
Canadian Research Institute for Food Safety, Department of Food Science, University of Guelph, Guelph, Ontario, Canada.
Int J Food Microbiol. 2021 Feb 2;339:108991. doi: 10.1016/j.ijfoodmicro.2020.108991. Epub 2020 Dec 1.
The survival of Listeria monocytogenes was assessed during long-term storage on three dried fruits: dried apples, raisins and dried strawberries. Using sand as a carrier, the dried fruits were dry-inoculated with a four-strain cocktail of L. monocytogenes to achieve numbers of 4.0 to 4.6 log CFU/g. The inoculated foods were stored at 4 °C, 25-81% relative humidity (RH) and 23 °C, 30-35% RH for 336 days. Colonies of L. monocytogenes could not be recovered from the dried apples after inoculation, i.e., day 0. Concentrations of L. monocytogenes decreased rapidly on the raisins and dried strawberries during storage at 23 °C, with enhanced survival observed at 4 °C. Linear rates of decline for populations of L. monocytogenes during storage at 4 °C on the raisins and dried strawberries were 0.1 and 0.2 log CFU/g/month, respectively. The relative distribution of the four L. monocytogenes strains making up the cocktail was determined by multiplex PCR at the beginning of storage and after 336 days on the dried fruits. At day 0, L. monocytogenes populations were predominantly composed of the serotype 1/2a and 3a strains on both the raisins and dried strawberries. After long-term storage at 4 °C, a relative decrease in serotype 1/2a was observed on both fruits, coupled with relative increases in the serotype 3a strain during storage on both fruits, in addition to the serotype 1/2b strain on the raisins. These results demonstrate that L. monocytogenes is rapidly inactivated during storage on raisins and dried strawberries at 23 °C, but it is capable of long-term survival at 4 °C. Improved knowledge on the survival of L. monocytogenes on these commodities is important for predictive modeling and can be used to better inform microbial health risk assessments.
对三种干制水果（干苹果、葡萄干和干草莓）在长期储存过程中李斯特菌的存活情况进行了评估。使用沙子作为载体，将李斯特菌的四菌株鸡尾酒干粉接种到干制水果中，达到 4.0 到 4.6 log CFU/g 的数量。接种后的食品在 4°C、25-81%相对湿度（RH）和 23°C、30-35% RH 下储存 336 天。在接种后，干苹果中无法再回收李斯特菌的菌落，即第 0 天。在 23°C 下储存时，葡萄干和干草莓上的李斯特菌浓度迅速下降，在 4°C 下观察到存活增强。在 4°C 下储存时，李斯特菌在葡萄干和干草莓上的种群线性下降率分别为 0.1 和 0.2 log CFU/g/月。在开始储存和在干制水果上储存 336 天后，通过多重 PCR 确定了构成鸡尾酒的四种李斯特菌菌株的相对分布。在第 0 天，李斯特菌种群主要由血清型 1/2a 和 3a 菌株组成，存在于葡萄干和干草莓上。在 4°C 下长期储存后，在两种水果上观察到血清型 1/2a 的相对减少，同时在两种水果的储存过程中观察到血清型 3a 菌株的相对增加，此外，在葡萄干上还观察到血清型 1/2b 菌株。这些结果表明，李斯特菌在 23°C 下储存时，在葡萄干和干草莓上迅速失活，但在 4°C 下能够长期存活。对这些商品上李斯特菌存活情况的深入了解对于预测模型非常重要，可用于更好地告知微生物健康风险评估。
