Study On The Correspondence Between Test Methods Of Coliforms In Foods And Its Current Limts

The standard detection methods of coliforms on foods stipulated by the state are GB/T 4789.3-2003 which is referred as 2003 method and its units is MPN/100g(mL)and GB 4789.3-2010. In GB 4789.3-2010, two counting methods are used, including coliforms MPN enumeration and coliforms plate enumeration, both of which are referred as 2010 MPN enumeration method and VRBA method, their units are MPN/g(mL) and CFU/g(mL) respectively. Nowadays, a great number of limit indexes of coliforms in foods are formulated according to the 2003 method. Because of the lack of the corresponding parameter values with the 2010 version, many companies and inspection agencies are still very confusing about selection method and judge of indexes, so easily leading to miss. So, the corresponding relation between the 2010 version of coliforms detection method and coliforms values in the product was studied in this paper.In this study, the sensitivity and the difference between method 2003 version and 2010 version MPN enumeration were firstly investigated by comparison of standard strain and samples. Then, the sensitivity and applicability of the two detection methods described in 2010 method were investigated. Finally, the corresponding relation between coliforms detection method in four kinds of foods(pickles,ice cream,pastries,meats) and coliforms values in the product was studied, which was used to establish the limit indexes of coliform correspond to 2010 version MPN enumeration. Meanwhile, the reasons of the number set parameter values in four kinds food and its applicability for various detection methods were analyzed.The main contents and conclusions were as follows:(1)The comparison of different testing methods showed that the sensitivity of 2003 version method was lower than the 2010 version, as bile salts of 2003 version was replaced sodium lauryl sulfate of 2010 version in beginning of fermentation medium by testing of standard strain and 50 samples. Besides, coliforms were modified by sodium lauryl sulfate.(2)Comparative study of VRBA method and plate counting method by standard strains, test results were 3.9×106MPN/mL,4.7×106MPN/mL respectively. It was proved that VRBA method had better sensitivity in the detection of E. coli.120 samples were detected by the 2010 version MPN enumeration and the VRBA method, It was shown that the unqualified rates were 10.8%,12.5%, respectively; Different sensitivity of 2010 version and VRBA was relatively low by comparision and and the VRBA method had better sensitivity. Because the MPN enumeration was the maximum probability, the VRBA method was accurate quantify,respectively; Hence,VRBA method should be used to detect food of infants and elderly people and related food,and should be modified the corresponding parameter values.(3)The results of the corresponding relation between coliforms detection method in four kinds of foods and index values in the product are shown below:The measured results of 50 units pickles in bags, ice cream, cold-working pastries were all qualified using 2003 version and 2010 version MPN enumeration whose index values was less than or equal to 0.3MPN/g,4.5MPN/g, 3MPN/g, respectively. Detection index was recommended in production and processing for pickles in bags and ice cream.It was shown that the unqualified rates of 50 units pickles in bags were 8%, 12%, respectively, the corresponding parameter values should be less than or equal to 0.9MPN/g, the unqualified rates of 50 units hot-working pastries were 6%,10%, respectively, the corresponding parameter values should be less than or equal to 3MPN/g.Meat:The current index research of 200 cooked meats with either jerky, dried meat floss, sauce braised meat or smoked and cooked ham. The results showed that the unqualified rates of method 2003 version were 0%,2%,10%, 4%, respectively; 2010 version MPN enumeration were 4%,4%,16%,6%, respectively. And limited index was less than or equal to 0.3MPN/g,0.4MPN/g, 1.5MPN/g,0.9MPN/g, respectively. Unqualified products originate from bulk products, it is suggested that the state should strengthen supervise of the bulk food, especially the sauce braised meat, and make appropriate adjustments for the index.The measured results of 25 units frozen poultry meat were qualified using 2003 version and 2010 version MPN enumeration whose index values was less than or equal to 100MPN/g. However, the reject rate of fresh meat was 2%, index values was less than or equal to 50MPN/g. It is not ideal that coliform was used as frozen food indicator bacteria because of damage for coliforms in frozen. Suggested that enterobacteriaceae will be used as frozen indicator bacteria and the test be set in the carcass before packing frozen after.(4)Eventually the 2010 edition will gradually replace the 2003 version of the method leading to the corresponding product standards being follow. That imply the index value of coliforms will also be updated. Due to the MPN enumeration method of the 2010 edition was over the 2003 version, the enterprises were proposed to pay attention to improve product quality, strengthen the production and health management.