DISPERSE, SURVIVE, PROPAGATE: MICROBIAL RESILIENCE IN THE SPOILAGE OF COMMERCIALLY PROCESSED FOODS

Abstract

Commercial spoilage in processed foods is an economic burden for manufacturers, and the etiological agents in these incidents represent some of the most resilient microorganisms in the food processing environment. Bacterial spores and the sexual spores of some filamentous fungi are the two most thermostable food-relevant propagules. Ascospores, hyphae, yeast cells, and conidia are each uniquely adept for dispersal in the production environment, while aciduric, thermophilic bacterial spore formers can survive and propagate under prototypical processing and storage conditions. Therefore, the goal of this project was to characterize the prevalence of microbial food spoilage incidents, identify the production conditions which select for particular spoilage organisms, and develop practices and controls to minimize the likelihood and severity of spoilage incidents. A survey of over 50 fruit and vegetable juice manufacturers revealed that 64% of respondents had faced quality threats from heat resistant molds and 78% were concerned with Alicyclobacillus spoilage. The vast majority (90%) of manufacturers indicated better control over microbial spoilage would increase profits and reduce waste. A prediction model was developed from an observational study assessing the ecology of fungi isolated from spoiled products submitted by industry collaborators. The outcomes at terminal nodes following recursive partitioning were included if they represented a ≥15% probability, which resulted in a decision tree with actionable outcomes for industry. Two examples from this collection of observations were explored further. Mucor circinelloides spoilage of yogurt was characterized under different thermal treatments, incubation conditions, and preservative regimes. Depending on a company’s control over sanitation programs and degree of risk aversion, maintenance of the cold chain or variable amounts of natamycin (>10 ppm) were determined to be sufficient intervention strategies to minimize spoilage from this post-processing, dimorphic contaminant. The spoilage potential variability of a collection of 53 food-sourced Alicyclobacillus isolates was also evaluated in various model systems. Citric acid was determined to significantly reduce the synthesis of guaiacol, the causative spoilage metabolite, which was produced variably across species from differing isolation sources. Collectively, these results may be useful in the development of in-plant quality controls and the selection of targets in validation and challenge studies.