ARC Industrial Transformation Training Centre for Food Safety in the Fresh Produce Industry, Sydney Institute of Agriculture, Faculty of Science, The University of Sydney, NSW 2006, Australia; The New Zealand Institute for Plant and Food Research Limited, Private Bag 92169, Auckland Mail Centre, Auckland 1142, New Zealand.
ARC Industrial Transformation Training Centre for Food Safety in the Fresh Produce Industry, Sydney Institute of Agriculture, Faculty of Science, The University of Sydney, NSW 2006, Australia.
Int J Food Microbiol. 2021 Mar 2;341:109069. doi: 10.1016/j.ijfoodmicro.2021.109069. Epub 2021 Jan 20.
Listeria monocytogenes has caused outbreaks of foodborne illness from apples in the USA, and is also a major issue for regulatory compliance worldwide. Due to apple's significance as an important export product from New Zealand, we aimed to determine the effect of long-term, low-temperature sea-freight from New Zealand to the USA (July) and Europe (March-April), two key New Zealand markets, on the survival and/or growth of L. monocytogenes on fresh apples. Temperature and humidity values were recorded during a shipment to each market (USA and Europe), then the observed variations around the 0.5 °C target temperature were simulated in laboratory trials using open ('Scired') and closed ('Royal Gala' for the USA and 'Cripps Pink' for Europe) calyx cultivars of apples inoculated with a cocktail of 10-10 cells of seven strains of L. monocytogenes. Samples were analysed for L. monocytogenes quantification at various intervals during the simulation and on each occasion, an extra set was analysed after a subsequent 8 days at 20 °C. When both the sea-freight simulations concluded, L. monocytogenes showed 5 log reductions on the equatorial surface of skin of apples, but only about 2.5 log reduction for USA and about 3.3 log reduction for Europe in the calyx. Cultivar type had no significant effect on the survival of L. monocytogenes for both sea-freight simulations, either in the calyx or on the skin (P > 0.05). Most of the reduction in the culturable cells on the skin occurred during the initial 2 weeks of the long-term storage simulations. There was also no significant difference in the reduction of L. monocytogenes at 0.5 or 20 °C. No correlation was observed between firmness or total soluble solids and survival of L. monocytogenes. Because the inoculated bacterial log reduction was lower in the calyx than on the skin, it is speculated that the risk of causing illness is higher if contaminated apple cores are eaten. The result suggested that the international sea-freight transportation does not result in the growth of L. monocytogenes irrespective of time and temperature. The results of this study provide useful insights into the survival of L. monocytogenes on different apple cultivars that can be used to develop effective risk mitigation strategies for fresh apples during long-term, low-temperature international sea-freight transportation.
单增李斯特菌已导致美国的食源性疾病暴发，并且也是全球监管合规的主要问题。由于苹果是新西兰重要的出口产品，我们旨在确定从新西兰到美国（7 月）和欧洲（3 月至 4 月）的长期低温海运对新鲜苹果上单核细胞增生李斯特菌的存活和/或生长的影响。在运往每个市场（美国和欧洲）的过程中记录了温度和湿度值，然后使用开放（“Scired”）和封闭（“Royal Gala”用于美国和“Cripps Pink”用于欧洲）花萼品种的苹果进行实验室试验，模拟了 0.5°C 目标温度周围的观察到的变化，这些苹果接种了七种李斯特菌菌株的 10-10 细胞混合物。在模拟过程中的不同时间间隔对李斯特菌进行定量分析，并在每次分析后，在 20°C 下再分析一组额外的样品。当海运模拟结束时，李斯特菌在苹果表皮赤道表面的数量减少了 5 个对数，但在花萼中，美国的减少量约为 2.5 个对数，欧洲的减少量约为 3.3 个对数。对于两种海运模拟，品种类型对李斯特菌在花萼或表皮上的存活均无显着影响（P>0.05）。在长期储存模拟的最初 2 周内，表皮上可培养细胞的大部分减少。在 0.5°C 或 20°C 下，李斯特菌的减少量也没有显着差异。未观察到硬度或总可溶性固体与李斯特菌存活之间的相关性。由于接种细菌的对数减少量在花萼中低于表皮，因此如果食用受污染的苹果芯，则患病的风险更高。结果表明，国际海运运输不会导致李斯特菌的生长，无论时间和温度如何。本研究结果提供了有关不同苹果品种上单核细胞增生李斯特菌存活的有用见解，可用于在长期低温国际海运过程中为新鲜苹果开发有效的风险缓解策略。
