Effects of suboptimal growth conditions on the subsequent UV-C resistance of Listeria monocytogenes in coconut liquid endosperm and apple juice

摘要

This study determined the ultraviolet-C (UVC) resistance ofListeria monocytogenesin coconut liquid endosperm and apple juice after previous exposures to suboptimal growth conditions.L. monocytogenes1/2c and 4b strains were individually exposed to gradual acidification (final pH 4.5), desiccation (aw0.96), heating (40?°C), and all their simultaneous combinations. Results showed that regardless of prior growth conditions and fruit beverage suspending medium,L. monocytogenesexhibited log-linear inactivation behavior. The UV-C energy dose necessary to reduce microbial population by 1 log cycle (DUV-C) varied across growth conditions and between fruit beverages. Regardless of growth condition,L. monocytogenesexhibited greater resistance in apple juice. In coconut liquid endosperm, the greatest UV-C resistance was observed in cells previously exposed to acidification and heat (A+H) (DUV-C37.32?mJ/cm2), while cells previously exposed to acidification and desiccation (A+D) exhibited the greatest resistance to UV-C in apple juice (DUV-C726.76?mJ/cm2).L. monocytogenesexhibited least UV-C resistance in coconut when previously exposed to heating (DUV-C25.40?mJ/cm2), while exposure to A+H resulted in least UV-C resistance when suspended in apple juice (DUV-C298.81?mJ/cm2). These results suggest that in addition to intrinsic suspending medium properties, implicit microbial physiology also affect the efficacy of UV-C treatment.