Effect of sporulation and recovery medium on the heat resistance and amount of injury of spores from spoilage bacilli

Aims: To assess the influence of sporulation media on heat resistance, and the use of stress recovery media to measure preservation injury of spores o f five representative spoilage bacilli. Methods and Results: Bacillus spores prepared on nutrient agar supplemented with Ca2+, Mg2+, Mn2+, Fe2+ and K+ were more heat-resistant than spores ob tained from nutrient agar with Mn2+. This increased heat resistance correla ted with a decrease in the protoplast water content as determined by buoyan t density sedimentation. The degree of preservation injury severity could b e assessed on media containing NaCl at moderate pH and organic acids at aci d pH. Ca-DPA, K+ or proline were added to the recovery media to demonstrate that heat probably caused injury to both spore germination and the outgrow th system. Significance and Impact of the Study: The metal content of sporulation medi a can strongly effect the validity of preservation resistance studies. The distinctive recovery media developed here can be relevant for assessing and comparing new preservation technologies.