title: Promoting Bacillus cereus spore germination for subsequent inactivation by mild heat treatment.
abstract: Sublethal heat treatment may activate dormant spores and thereby potentiate the conversion of spores to vegetative cells. As the germinated spore is known to possess lower heat resistance than its dormant counterpart, it has been postulated that double heat treatment, i.e., spore heat  activation followed by germination and then by heat inactivation, can be used to control spores in foods. Production of refrigerated processed foods of extended durability often includes more than one heat treatment of the food components. This work simulates conventional heat treatment procedures  and evaluates double heat treatment as a method to improve spore control in model food matrixes of meat broth and cream sauce. Bacillus cereus NVH 1230-88 spores were supplemented in food model matrixes and heat activated at 70°C and then heat inactivated at 80 or 90°C. The  samples were held at 29 to 30°C for 1 h between primary and secondary heat treatments, to allow spore germination. Nutrients naturally present in the food matrixes, e.g., amino acids and inosine, could act as germinants that induce germination. The levels of germinants could be too low  to produce effective germination within 1 h. Following primary heat treatment, some samples were therefore supplemented with a combination of L-alanine and inosine, a germinant mixture known to be effective for B. cereus spores. In both matrixes, a combination of double heat treatment  (heat activation, germination, and inactivation) and addition of germinants gave a reduction in spore counts equivalent to or greater than that obtained with a single heat treatment for 12 min at 90°C. Addition of germinants was essential to induce effective germination in cream sauce  during 1 h at 29 to 30°C, and germinants were therefore a crucial supplement to obtain an effect of double heat treatment in this matrix. These data will be valuable when setting up temperature-time-germinant combinations for an optimized spore reduction in mild-heat-treated foods.
authors.affiliation: Nofima AS, Department of Process Technology, P.O. Box 8034, N-4068 Stavanger, Norway.
authors.forename: Irene Stranden
authors.initials: IS
authors.lastname: Løvdal
authors.forename: Maria Befring
authors.initials: MB
authors.lastname: Hovda
authors.forename: Per Einar
authors.initials: PE
authors.lastname: Granum
authors.forename: Jan Thomas
authors.initials: JT
authors.lastname: Rosnes
mesh_terms: D001409:Bacillus cereus / Q000502:physiology*; D015169:Colony Count, Microbial; D005506:Food Contamination / Q000032:analysis / Q000517:prevention & control*; D005516:Food Microbiology; D059022:Food Safety; D006358:Hot Temperature; D006801:Humans; D008461:Meat Products / Q000382:microbiology*; D013171:Spores, Bacterial