Yu Zhongjia, Joossens Marie, Kerkhof Pieter-Jan, Houf Kurt
Department of Veterinary Public Health and Food Safety, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, Karel Lodewijk Ledeganckstraat 35, Ghent, Belgium.
Int J Food Microbiol. 2021 Feb 16;340:109051. doi: 10.1016/j.ijfoodmicro.2021.109051. Epub 2021 Jan 18.
Freezing broiler carcasses, industrially or at home, not only delays spoilage, but also is expected to increase food safety by hampering growth of food pathogens. However, detailed knowledge on microbial changes after a short or longer freezing period of fresh broiler meat in home freezing setting is lacking and no comparison between different freezing periods has been published yet. The present study combined classical isolation techniques and identification by MALDI-TOF MS with 16S rRNA amplicon sequencing to assess bacterial contamination on broiler carcasses that were either bought fresh and then frozen for short periods (total n = 20) in home freezing, or industrial frozen one (total n = 4) at retail. Changes in total aerobic bacteria (TAB) were also studied on 78 freshly bought broiler carcasses that were then stored frozen for up to 6 months in domestic freezers. Salmonella and Campylobacter were examined to assess the effect of freezing on controlling common foodborne pathogens. The contamination level of mesophilic and psychrotrophic TAB was numerically equal on carcasses at retail, either fresh or frozen at different time points. After short and long freezing period, a decrease in counts of mesophilic TAB was observed, while changes in counts of psychrotrophic TAB were rarely observed. No correlation between home freezing period and TAB load, either mesophilic (R = -0.006, p = 0.949) or psychrotrophic (R = 0.080, p = 0.389), was observed. No Salmonella and Campylobacter was detected on industrial frozen carcasses but on fresh carcasses at retail, either pre-freezing or after freezing. The bacterial communities were influenced by freezing, in which some genera showed significantly changes in relative abundance after freezing. In conclusion, from a food safety point of view, freezing of meat products does not serve as safety hurdle, and freezing should only be considered as a method for extending shelf life compared with fresh chicken meat. Applying hygienic slaughter procedures to keep the initial contamination as low as possible, and the maintenance of the cold chain during further processing are the key factors in food safety.
在工业环境或家庭环境中冷冻肉鸡胴体，不仅可以延缓其腐败变质，而且有望通过抑制食源性病原体的生长来提高食品安全。然而，目前缺乏关于在家用冷冻条件下新鲜肉鸡胴体经过短期或长期冷冻后微生物变化的详细知识，并且尚未有关于不同冷冻期之间比较的报道。本研究将经典的分离技术、基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）鉴定与16S rRNA扩增子测序相结合，以评估在家用冷冻条件下新鲜购买后短期冷冻（总共n = 20）的肉鸡胴体或零售时工业冷冻的肉鸡胴体（总共n = 4）上的细菌污染情况。还对78只新鲜购买的肉鸡胴体进行了研究，这些胴体随后在家用冰箱中冷冻储存长达6个月，以研究总需氧菌（TAB）的变化。检测了沙门氏菌和弯曲杆菌，以评估冷冻对控制常见食源性病原体的效果。在零售时，无论是新鲜的还是在不同时间点冷冻的胴体上，嗜温性和嗜冷性TAB的污染水平在数值上是相等的。经过短期和长期冷冻后，观察到嗜温性TAB数量减少，而嗜冷性TAB数量的变化很少被观察到。在家用冷冻期与TAB负荷之间，无论是嗜温性（R = -0.006，p = 0.949）还是嗜冷性（R = 0.080，p = 0.389），均未观察到相关性。在工业冷冻的胴体上未检测到沙门氏菌和弯曲杆菌，但在零售的新鲜胴体上，无论是冷冻前还是冷冻后均检测到。细菌群落受到冷冻的影响，其中一些属在冷冻后相对丰度出现了显著变化。总之，从食品安全的角度来看，肉类产品的冷冻并不能作为安全屏障，与新鲜鸡肉相比，冷冻仅应被视为延长保质期的一种方法。采用卫生的屠宰程序以尽可能降低初始污染，以及在进一步加工过程中维持冷链是食品安全的关键因素。
