Inactivation of Salmonella, E. coli and Listeria monocytogenes in phosphate-buffered saline and apple juice by ultraviolet and heat treatments

Two strains of Escherichia coli (K-12 and O157:H7), Salmonella (enteritidis and typhimurium) and Listeria monocytogenes (AS-1 and M24-1) were individually suspended in phosphate-buffered saline (PBS) and apple juice prior to exposure to UV radiation (220–300 nm) and heating at 55 °C. The calculated decimal reduction times (D value, min) varied with suspending medium and mode of inactivation. The AS-1 and M24-1 strains of L. monocytogenes were found to be most resistant to UV in PBS (0.28–0.29 min) while the AS-1 strain was most resistant in juice (1.26 min). The AS-1 strain of L. monocytogenes and E. coli O157:H7 were most heat resistant when suspended in PBS (4.41 min) and juice (4.43 min), respectively. Results obtained from this study may be used by apple juice processors in selecting appropriate organisms for UV irradiation or heat treatment lethality validations.