Abstract
Bacterial spores often survive thermal processing used in the food industry, while heat treatment leads not only to a decrease in the nutritional and organoleptic properties of foods, but also to a delay in fermentation of fermented foods. Selective reduction of undesirable spores without such impediments is an ongoing challenge for food scientists. Thus, increased knowledge of the spore-forming bacteria is required to control them. In this study, the heat resistance results (D100°C) of the spores of four Bacillus species were determined and compared to previous literature, and found that B. cereus has significantly lower heat resistance than the other Bacillus species, B. coagulans, B. subtilis, and B. licheniformis. Using the spores of these strains, this study also evaluated the effects of single and combined supplementation of calcium (0.00–2.00 mM) and manganese (0.00–0.50 mM) on heat resistance (D100°C). The results revealed that the spores of B. licheniformis and B. cereus displayed the smallest heat resistance when sporulated on media rich in calcium. Conversely, B. coagulans spores and B. subtilis spores exhibited the greatest heat resistance when sporulated under calcium-rich conditions. The opposite results (stronger heat resistance for B. licheniformis spores and B. cereus spores, and smaller heat resistance for B. coagulans spores and B. subtilis spores) were obtained when the spores were formed on media poor in the minerals (particularly calcium). Based on the results, the Bacillus species were divided into two groups: B. licheniformis and B. cereus; and B. coagulans and B. subtilis. The study provides valuable insight to selectively reduce spores of undesirable Bacillus species in the food industry.
Highlights
Spore-forming bacteria form a dormant, metabolically inert structure called a spore when encountering environmental stress factors such as nutrient exhaustion or starvation
Heat resistance profiles of spores of B. licheniformis, B. cereus, B. coagulans, and B. subtilis formed on basal media without mineral supplementation were compiled in Figure 2
It is noteworthy that, for the above comparison, all literature data as much as possible were collected based on the following criteria: (1) minerals should not be added into the sporulation media in spore crop preparation and (2) D100◦ C-values should be obtained through heat treatment in a solution with a pH of approximately 7.0
Summary
Spore-forming bacteria form a dormant, metabolically inert structure called a (endo) spore when encountering environmental stress factors such as nutrient exhaustion or starvation. The application of conventional sterilization methods is often limited in food processing since high-intensity treatments can decrease the nutritional value and organoleptic characteristics of foods. Excessive heat treatment can reduce the number of beneficial bioactive microorganisms in fermented foods and/or delay the fermentation of foods (Mah et al, 2019), which limits the application of sterilization processes to the production of fermented food products. Due to this, eliminating or reducing spore contamination is one of the keys to guarantee the safety of foods such as fermented food products. Information on the heat resistance of spores in various environments is important for the development of a precise heat treatment process that minimizes both the risk of spores and the loss of nutrients in the food industry
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