Thermal Inactivation Kinetics of Sporolactobacillus nakayamae Spores, a Spoilage Bacterium Isolated from a Model Mashed Potato-Scallion Mixture

Sporolactobacillus species have been occasionally isolated from spoiled foods and environmental sources. Thus, food processors should be aware of their potential presence and characteristics. In this study, the heat resistance and influence of the growth and recovery media on apparent heat resistance of Sporolactobacillus nakayamae spores were studied and described mathematically. For each medium, survivor curves and thermal death curves were generated for different treatment times (0 to 25 min) at different temperatures (70, 75, and 80 degrees C) and Weibull and first-order models were compared. Thermal inactivation data for S. nakayamae spores varied widely depending on the media formulations used, with glucose yeast peptone consistently yielding the highest D-values for the three temperatures tested. For this same medium, the D-values ranged from 25.24 +/- 1.57 to 3.45 +/- 0.27 min for the first-order model and from 24.18 +/- 0.62 to 3.50 +/- 0.24 min for the Weibull model at 70 and 80 degrees C, respectively. The z-values determined for S. nakayamae spores were 11.91 +/- 0.29 degrees C for the Weibull model and 11.58 +/- 0.43 degrees C for the first-order model. The calculated activation energy was 200.5 +/- 7.3 kJ/mol for the first-order model and 192.8 +/- 22.1 kJ/mol for the Weibull model. The Weibull model consistently produced the best fit for all the survival curves. This study provides novel and precise information on thermal inactivation kinetics of S. nakayamae spores that will enable reliable thermal process calculations for eliminating this spoilage bacterium.