Research on the Production Procedure of Escherichia coli and Salmonella Reference Material on Pork Matrix Using for Proficiency Testing

This study aims to develop the procedures for the production of Escherichia coli (E. coli) and Salmonella reference material on pork matrix, using for the proficiency testing in food safety assessment. Microorganisms are managed by freezing, deep freezing, and freeze-drying. The freezing method helps microorganisms survive and stabilize for a long time under normal temperature conditions. Freeze-drying is a complicated technique and requires research on possible substrate components and preservatives to ensure solubility, porosity, and high survival rate of the final product as microbiological reference material. Two considered important characteristics of the reference material are homogeneity and stability. The compositions of the input material were identified to create a stable state and a good recovery rate by evaluating the homogeneity and continued stability monitoring. The procedure includes: i) Preparation of microorganisms and material creation; ii) Assessment of physical properties of the material: porosity, uniformity rate, dissolubility; iii) Quantitative testing the homogeneity and the stability of the freeze-drying bacterial reference material; and iv) Application of the produced freeze-drying of E. coli and Salmonella reference material used in the proficiency testing program. The results show that the standard sample achieves a good physical state and meets the requirements for homogeneity and stability according to ISO 13528:2022.