Abstract
The resistance formation of spores in general and of Bacillus atrophaeus in particular has long been the focus of science in the bio-defense, pharmaceutical and food industries. In the food industry, it is used as a biological indicator (BI) for the evaluation of the inactivation effects of hydrogen peroxide in processing and end packaging lines’ sterilization. Defined BI resistances are critical to avoid false positive and negative tests, which are salient problems due to the variable resistance of currently available commercial BIs. Although spores for use as BIs have been produced for years, little is known about the influence of sporulation conditions on the resistance as a potential source of random variability. This study therefore examines the dependence of spore resistance on the temperature, pH and partial oxygen saturation during submerged production in a bioreactor. For this purpose, spores were produced under different sporulation conditions and their resistance, defined by the D-value, was determined using a count reduction test in tempered 35% liquid hydrogen peroxide. The statistical analysis of the test results shows a quadratic dependence of the resistance on the pH, with the highest D-values at neutral pH. The sporulation temperature has a linear influence on the resistance. The higher the temperature, the higher the D-value. However, these factors interact with each other, which means that the temperature only influences the resistance when the pH is within a certain range. The oxygen partial pressure during sporulation has no significant influence. Based on the data obtained, a model could be developed enabling the resistance of BIs to be calculated, predicted and standardized depending on the sporulation conditions. BI manufacturers could thus produce BIs with defined resistances for the validation of sterilization effects in aseptic packaging/filling lines for the reliable manufacture of shelf-stable and safe food products.
Highlights
In the food and pharmaceutical industry, sterility in production and packaging is extremely important in many instances
Certain standard BI strains have been established, and these are routinely applied at the industrial level in validation test runs of filling machines, for instance. These BIs have a high level of resistance against certain inactivation methods using, e.g., H2 O2, which covers the requirements in specific situations, e.g., in the food industry, filling neutral liquid products, or in the pharmaceutical industry
In order to be able to investigate the influence of the sporulation conditions on the resistance of the spores, a model had to be developed with which it is possible to make statistically significant statements about the influences on the resistance by varying the sporulation conditions
Summary
In the food and pharmaceutical industry, sterility in production and packaging is extremely important in many instances. Pathogenic and spoilage-inducing spore formers can be dangerous, since the spores, because of their high resistance, can survive pasteurization and inadequate sterilization processes and germinate, contaminating the sterile product filled into nonsterile containers As a result, they either significantly reduce the shelf life of the food or can even be harmful to consumers. Certain standard BI strains have been established, and these are routinely applied at the industrial level in validation test runs of filling machines, for instance These BIs have a high level of resistance against certain inactivation methods using, e.g., H2 O2 , which covers the requirements in specific situations, e.g., in the food industry, filling neutral liquid products, or in the pharmaceutical industry.
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