Previous stress exposures influence subsequent UV-C resistance of Salmonella enterica in coconut liquid endosperm

- Logarithmic linear inactivation behavior was observed in all stressed organisms.
- Sublethal injury was observed in all stressed organisms but were not significantly different.
- Heterologous adaptation to UV-C was observed in singular and combined stresses.
- Heat stress induced highest resistance to ultraviolet-c irradiation.

This study determined the effects of prior exposures to stresses commonly encountered by cells in food production and processing environments on the subsequent UV-C inactivation rates of Salmonella enterica in coconut liquid endosperm. Seven different strains of S. enterica were separately exposed to individual stresses such as gradual acidification (final pH 4.5), abrupt desiccation (aw 0.96), or heat stress at 40 °C for 24 h, after which the test strains were cocktailed and subjected to UV-C challenge. Cells were also exposed to all possible combinations of the individual stresses and thereafter subjected to UV-C challenge. Cells exposed to all individual and combinations of stresses exhibited 1st order, log-linear inactivation behavior (R2 0.903 to 0.998). Cells previously exposed to singular heat stress had the highest UV-C resistance (DUV-C 43.8 mJ/cm2), while cells exposed to all simultaneous pH, aw, and heat stresses had the least (DUV-C 22.5 mJ/cm2). Heterologous adaptive mechanisms were observed after S. enterica cells were exposed to acid, acid + desiccation, heat, and acid + heat, with individual heat stress exposure resulting in the significantly most UV-C resistant cells. Results obtained in this study provide baseline information on the selection of appropriate challenge organism for establishment of UV-C process schedule for coconut liquid endosperm and similar commodities.