Inactivation of Bacillus subtilis spores by combined pulsed light and thermal treatments

Abstract

The combined effect of pulsed light (PL) and heat processing was evaluated on the inactivation of Bacillus subtilis spores. Those processes were applied separately and the time between both treatments was modified to evaluate whether the effect of the first treatment is maintained for a longtime. B. subtilis spores subjected to sublethal pretreatments were more sensitive to subsequent treatments (PL or thermal treatments) than untreated spores. Heating followed by PL was the most effective combination in reducing B. subtilis counts. Bacterial spores remained sensitized to subsequent treatment for at least 24 h of storage in water, whatever the temperature was (4 or 30 degrees C). Sensitivity of B. subtilis cells to PL or heat processing increased after germination in a nutrient broth, being equally sensitive from 3 to 24 h. Vegetative cells maintained their enhanced sensitivity to subsequent processing after spore germination. The results of this work demonstrate that the combination of heating and PL treatment is a promising preservation method for microbial inactivation. (C) 2015 Elsevier B.V. All rights reserved.