冷链物流过程猪肉微生物污染与控制图设计

Microbial contamination of chilled pork in cold chain logistics and its control chart design

为科学监控猪肉冷链物流过程的微生物污染和产品质量安全,该研究检测冷却猪肉物流环节主要腐败菌和病原菌的数量变化,设计基于统计过程控制的均值-极差控制图,用以分析物流过程微生物数量的波动性和产品合格率。结果表明:猪肉微生物数量随着物流链的延长而显著增加(大肠菌群除外),超市货架肉块的微生物数量显著高于屠宰场待出货样品,且外市超市显著高于本市超市。物流过程猪肉的菌落总数、大肠菌群和热杀索丝菌的数量均符合正态分布,假单胞菌和李斯特菌的数量不符合正态分布。根据猪肉中微生物不同限量标准控制线所得到的过程能力指数和产品合格率不同,但样品中的菌落总数均符合国家标准。均值-极差控制图可以直观呈现微生物数量的波动性和产品合格率,为监控猪肉冷链物流过程或操作工序的微生物污染提供科学的管理和控制方法。

The quantity changes of major spoilage microflora （total viable counts, Pseudomonas sp. and Brochothrix thermosphacta） and pathogen microflora （Coliform bacteria and Listeria sp.） during the cold chain logistics were investigated by selective medium, to evaluate the quality and safety of chilled pork by monitoring the microbial growth. The mean-range control chart of microbial contamination of chilled pork during the logistics chain was designed using the statistical process control technology, to analyze their quantity fluctuation and the ratio of eligible quality. The results showed that the microbial quantity （except Coliform bacteria） of pork samples increased significantly （P〈0.05） with the extension of logistics chain, and the quantity of pork samples in supermarket were higher （P〈0.05） than those in slaughterhouse;The microbial contamination of pork samples in the supermarket from external city was higher （P〈0.05） than those from local city. The microbial quantity distribution of chilled pork during the logistics chain was studied by normality test, and it was found that the quantity of Coliform bacteria and Brochothrix thermosphacta showed normal distribution, but Pseudomonas sp. and Listeria sp. did not fit normal distribution. The mean-range control chart of total viable counts and Coliform bacteria of chilled pork during the logistics chain was designed using statistical process control technology, according to the microbial safety limits of chilled pork in the national standard of the People＇s Republic of China. As showed in the control charts, there were significantly differents in the process capability index （CPk） and the ratio of quality eligibility calculated by different control limits from zero to alerting limit, from zero to maximum limit, and from lower control limit （LUL） to upper control limit （UCL）. However, the total viable counts in all pork samples were eligible according to the national microbial quantity limits （1×106cfu/g）. Mean-range control chart can be used to show intuitively the abnormal fluctuations and substandard quality of microorganism, and it is not yet or seldom applied to the microbial contamination of pork in the cold chain logistics. The research is meaningful to provide a scientific method in pork quality monitoring and microbial control in the cold chain logistics.