Importance of strain selection to conduct challenge test and assess food spoilage

Introduction: To comply with EC regulation, it is the responsibility of the food business operator to control microbial hazards in foods under foreseeable conditions of production, storage, purchase, and use. For that matter, predictive mathematical models and challenge testing are recognized approaches used to validate control measures within the HACCP system, as well as to assess microbiological food safety and quality. Purpose: This work aimed at the industrial application and transfer from mathematical models validated for pathogens to Bacillus spp., in order to assess potential rope spoilage in bread. Methods: Growth cardinal values are microbiologically relevant parameters. Even though time consuming, the determination of such values enable the determination of growth/no growth boundaries for given food product formulation and storage conditions (pH, water activity (aw), temperature). Based on known cardinal values of Bacillus spp. strains, challenge testing was performed with artificial spore inoculation into bread dough. After baking, the enumeration of Bacillus spp. from bread in storage (30°C) was performed. Growth kinetics were ?tted to mathematical models to further enable in silico simulations during bread shelf-life for storage scenarios mimicking Mediterranean temperature. Results: Growth/no growth boundaries clearly showed variable growth abilities in bread for the different Bacillus strains selected. A challenge test was performed with the strain isolated from wheat grain that showsed wider growth abilities regarding low aw. In silico simulations were performed to quantify Bacillus spp. populations during shelf-life and to determine the probability of overpassing a given ?ve log/g contamination. Growth simulationsunderline that rope spoilage showed rapid evolution and, mainly, occurs in the summer season in Mediterranean countries. Significance: To facilitate the practical use of generic and recognized mathematical models, several user-friendly tools exist for growth prediction. Besides the importance of using real-life strains, this study further underlined the importance of characterized collections for the selection of the bacterial strain(s) to be used in the challenge test to ensure food quality and safety during shelf-life.