Microbial test organisms for sterilization processes in food industry

Sammanfattning: The importance of sterilization processes has been a major topic in the food manufacturing industry since it preserves the quality and provides longer shelf-life by preventing microbiological recontamination of products. Aseptic packaging is an alternative technique to pack commercially sterile products into containers with a very low recontamination rate, thus, the entire production chain must be designed according to the aseptic condition, including the packaging material, the filling machines, and the surrounding area where the process takes place. To evaluate a sterilization process, there is a validation test in which the process is challenged with certain test organisms. VDMA or Verband Deutscher Maschinen- und Anlagenbau (German Engineering Federation) has published a guideline (FS NuV No. 10/2005 Appendix A) containing the recommendation of the required outcomes for the validation test of the filling machines depending on the sterilization processes and test organisms. Furthermore, the guideline has motivated us to obtain further confidence data on the performance of the test organisms. The present study aimed to investigate and compare the resistance of spore-producing organisms, A. brasiliensis, B. atrophaeus, and B. subtilis, against different disinfection/sterilization processes relevant to the food industry as indicated by VDMA, i.e. chemical (hydrogen peroxide and peracetic acid products of Oxonia), thermal (steam, hot water, and dry heat), as well as UV irradiation. A review of existing research was then compiled with the laboratory results to suggest suitable test organisms depending on the sterilization processes applied. Based on the observations, B. subtilis spores are the test organism that showed highest resistance against H2O2 and Oxonia sterilization process with D60 °C = 6,17 s and Dambient = 13,89 s respectively. This result was in accordance with the guidelines of VDMA. For the thermal processes, VDMA suggested A. brasiliensis spores as the recommended test organisms. However, our findings resulted that for disinfection and sterilization processes that employ hot water and dry heat, B. atrophaeus spores were found as the ideal test organism exhibiting the desired resistance towards the given processes with a D90 °C and D121 °C of 8,1 min and 71,94 min. Our review study on steam sterilization suggested G. stearothermophilus as the suitable test organisms for steam sterilization, although VDMA suggested A. brasiliensis spores. Throughout the study, A. brasiliensis spores have demonstrated rapid reductions for all the sterilization process evaluated, indicating low resistance and therefore were not considered as an ideal test organism to use. However, when looking into the available literature on UV irradiation, it was found that A. brasiliensis could be a possible test organism to assess its effectiveness considering its black spore pigment, aspergillin, which is responsible to the high UV resistance as it absorbs high amounts of the UV radiation to protect the cell.