Prior physicochemical stress exposures and subsequent UV-C resistance of E. coli O157:H7 in coconut liquid endosperm

Abstract

This study determined the effects of prior exposures to individual acid, desiccation, and heat stress, and all their possible simultaneous combinations, on the subsequent ultraviolet-C (UV-C) inactivation kinetics of E. coli O157:H7 in a coconut liquid endosperm suspending medium. Sublethal injury rates determined in the cells after stress exposure and acclimation in the suspending medium ranged from 0.00% (acid stressed) to 84.24% (desiccation+heat stressed). Regardless of the previous stress to which cells were exposed, a logarithmic linear inactivation behavior was observed in the cells. The decimal reduction energy (DUV-C) of the stressed cells ranged from 152.17mJ/cm2 (acid+desiccation+heat stressed) to 209.81mJ/cm2 (acid+heat stressed). No apparent relationship was observed between % injury and DUV-C values possibly because the nature of the injury the cells incurred after exposures to the stresses was not determined. Cells previously exposed to the combined acid and heat stress exhibited the highest D ratio (DUV-C stressed/ DUV-C control), indicative of heterologous adaptation that resulted in cells 30% more resistant towards UV-C. The results established in this study contribute in further understanding the utility and limitations of UV-C radiation as an alternative nonthermal processing technique for fruit juices.