食品检测用大肠埃希氏菌标准物质的研制

Preparation of Escherichia coli reference materials for food detection

目的研制食品检测用大肠埃希氏菌标准物质。方法采用冷冻干燥技术制备含量为4×104~5×104 CFU/样品的标准物质,参照CNAS—GL29:2010《标准物质/标准样品定值的一般原则和统计方法》,随机抽取20件样品进行均匀性检验,采用单因素方差分析对结果进行统计分析;将样品分别于-20、4、25℃条件下保藏,对其储藏稳定性和运输稳定性进行评价;并组织3家实验室进行协同标定;并使用20件食品作为基质,按照GB 4789.3—2016《食品安全国家标准食品微生物学检验大肠菌群计数》检验大肠埃希氏菌标准物质的适用性。结果均匀性检测单因素方差分析结果为F=1.933(P=0.076),符合标准物质的要求。标准物质在-20℃保藏28 d,复苏率为96.2%;在4℃保藏14 d,复苏率为77.0%;25℃保藏7 d,样品中菌含量仍保持在104 CFU/样品的水平。综上所述,标准物质的短期储藏稳定性、长期储藏稳定性和运输稳定性均符合要求。经3家实验室协同标定,样品中活菌含量均在104 CFU/样品水平,生化鉴定结果为大肠埃希氏菌;标准物质在20种食品基质的回收率为54.9%~96.6%。结论本研究所制备的大肠埃希氏菌标准物质的均匀性、储藏稳定性和运输稳定性均符合要求,适用性良好,可用于食品检测实验室的质量控制和食品中大肠埃希氏菌检测结果的评价。

Objective To prepare Escherichia coli(E.coli)reference materials for food detection.Methods The reference materials with a content of 4×104-5×104 CFU/sample were prepared by freeze-drying method,20 samples were selected randomly for homogeneity determination and the results were analyzed by one-way analysis of variance according to CNAS—GL29:2010 Reference materials-General and statistical priciples for certification;The samples were stored at-20,4,and 25℃to evaluate the storage stability and transport stability,respectively.Then 3 laboratories were organized for collaborative calibration;Additionally,20 kinds of food samples were selected as the matrices to test the applicability of the reference materials according to the GB 4789.3—2016 National food safety standard-Food microbiological testing-E.coli population counts.Results The one-way analysis of variance result of homogeneity determination was F=1.933(P=0.076),which met the homogeneity requirement for reference materials.The recoveries of reference materials reached 96.2%after storaged at-20℃for 28 d,and 77.0%after storaged at 4℃for 14 d;And the content of E.coli remained the level of 104 CFU/sample after storaged at 25℃for 7 d.In conclusion,the short-term storage stability,long-term storage stability and transportation stability of the reference materials all met the requirements.The live bacteria content in the samples was all at the level of 104 CFU/sample,and the biochemical identification results were confirmed as E.coli by the collaborative calibration with 3 laboratories;Additionally,the recoveries of reference materials in 20 kinds of food substrates were 54.9%-96.6%.Conclusion The homogeneity,storage stability and transportation stability of E.coli reference materials prepared in this study can meet the requirements for reference materials and has good applicability,which can be used for quality control of food testing laboratory and evaluation of detection results of E.coli in food.