Head space indicators monitoring the growth of B. cereus and Cl. perfringen in aseptically packed meat soup

The growth characteristics of Bacillus cereus and Clostridium perfringens were followed in meat soup during the preincubation period at 30°C for 14 d. The microbes were UV-treated before inoculation. The control group was inoculated without UV-treatment. The food packs were sealed in plastic bags containing different headspace gas constituents (20% oxygen + 80% nitrogen or 100% nitrogen). The growth of the test bacteria were recorded every 2 d by cultivating and checking the headspace oxygen and carbon dioxide. The UV-treatment did not have a significant effect on the outcome of the growth of either bacterium. B. cereus grew well in both nitrogen and air-flushed packages whereas C. perfringens did not survive as well in air-flushed packs. The production of CO₂ was influenced by the initial headspace composition which was also checked by powder-based redox indicators sealed in the packages. The colour changes measured through the package laminate by Minolta Chromameter correlation well with microbial growth in the food packs.