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In this work, we have used spores of Bacillus subtilis that specifically induce bioluminescence upon initiation of germination as a rapid, real-time monitor of the effects of preservative treatments on germination. Using this tool, we have demonstrated that the combination of mild acidity (pH 5.5 to 5.0), lactic acid (0.5%), and a pasteurization step (90°C for 5 min) results in enhanced inhibition of spore germination compared with the effects of the individual treatments alone. Inhibition by the combination treatment occurred as a result of both direct but reversible inhibition, entirely dependent on the physical presence of the preservative factors, and permanent, nonreversible damage to the L-alanine germination apparatus of the spore. However, we were able to restore germination of the preservative-damaged spores unable to germinate on L-alanine by supplementing the medium with the nonnutrient germinant calcium dipicolinic acid. The demonstration that simple combinations of preservative factors inhibit spore germination indicates that food preservation systems providing ambient stability could be designed which do not adhere to the strict limits set by commonly accepted processes and which are based on precise understanding of their inhibitory action.Food manufacturers rely mainly on preservation by moist heat to produce ambient-stable products. These products are traditionally classified as low-acid foods, with pH values greater than 4.5, and medium-or high-acid foods, with pH values less than 4.5. The division is a reflection of the inability of spores of Clostridium botulinum and other mesophilic sporeformers to outgrow in foods with pH values of 4.5 or less (4). Thus, to ensure microbiological safety, low-acid foods are given severe heat treatments (121°C for 3 min or equivalent) which are designed to cause a 12-log reduction in the number of C. botulinum spores but which often result in foods with poor taste and organoleptic quality.The target organisms for any low-acid preservation system providing ambient stability are endospore-forming bacteria of the genera Bacillus and Clostridium. The bacterial spore acts as a survival stage which is characterized by high resistance to heat and other adverse conditions typically used to kill vegetative cells (reviewed in reference 20). In foods, the spore itself does not represent a hazard. However, despite being metabolically dormant, the spore has a functional environmental sensory mechanism that can trigger germination under favorable conditions. Thus, the process of germination, outgrowth and proliferation, and/or toxin formation can result in spoilage and/or food poisoning.Germination of Bacillus subtilis spores can be initiated upon exposure to two distinct types of nutrient stimuli: (i) L-alanine and (ii) a combination of L-asparagine, glucose, fructose, and KCl (AGFK) (28, 29). Subsequent work showed that metabolism of these nutrients did not occur during the process of germination (25) and that these molecules initiated germination by binding and activati...

Mathematical models have been developed which describe the effect of lowering the water activity on the growth kinetics of Staphylococcus aureus and Salmonella typhimurium. By treating the lag phase and exponential phase kinetics separately predictions can be made on the extent of microbial growth over successive time/temperature cycles. Staph. aureus was far more tolerant than Salm. typhimurium to lowered water activity and under near growth limiting conditions of water activity and temperature was showing lag periods as long as ca 40 d. The maximum lag period observed for Salm. typhimurium was ca 5 d. Under these conditions the predicted generation times for Staph. aureus were 2-3 d and for Salm. typhimurium.

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The distribution of micro‐organisms within batches of food is identified as log‐normal and this distribution has practical implications in the control of microbial hazards in foods. These implications are explained as effects upon counting procedures, changes in levels through processes, detection of low levels of micro‐organisms, the use of indicator groups, presence/absence tests, consumer safety calculations, and sample unit size analysed.