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Fate of E. coli O157:H7, Salmonella spp. and potential surrogate bacteria on apricot fruit, following exposure to UV-C light

Yun, Juan, Yan, Ruixiang, Fan, Xuetong, Gurtler, Joshua, Phillips, John
International journal of food microbiology 2013 v.166 no.3 pp. 356
Escherichia coli O157, Salmonella typhimurium, apricots, bacteria, hardness, sanitizers, temperature, ultraviolet radiation
Some soft fruit, such as tree-ripened apricots, cannot be washed with aqueous sanitizers, due to their innate softness and delicate surfaces. In this study, ultraviolet-C (UV-C) light was investigated for its efficacy in inactivating 4–5 individual strains of Escherichia coli O157:H7 and Salmonella spp. on apricots, in addition to a four-strain composite of Shiga toxin-negative E. coli O157:H7 and a cocktail of three attenuated strains of Salmonella Typhimurium and Salmonella Typhimurium LT2. Also, the survival of E. coli O157:H7 and Salmonella spp. after exposure to 74 and 442mJ/cm2 of UV-C was evaluated during post-UV storage at 2 and 20°C. The fruit was spot inoculated and the areas (ca. 1.5cm2) of fruit surface with the inoculated bacteria were exposed to UV-C at 7.4mW/cm2. E. coli O157:H7 and Salmonella spp. populations decreased rapidly (1–2 logs) (P<0.05) with increasing UV-C doses of 0 to 74mJ/cm2. Further increases in UV-C dosage achieved only limited additional reductions in bacterial populations. Shiga toxin-negative bacteria and attenuated S. Typhimurium strains, along with S. Typhimurium LT2, responded similarly to corresponding pathogenic E. coli O157:H7 and Salmonella spp. During storage at 2 or 20°C, populations of pathogenic E. coli O157:H7 and Salmonella spp. on untreated fruit decreased slowly; however, populations on fruit treated with 442mJ/cm2 decreased rapidly at both temperatures. After 8days at 20°C or 21days at 2°C, E. coli O157:H7 and Salmonella spp. populations on UV-C treated fruit were at least 2logCFU/g lower than on non-treated controls. Our results suggest that surface-inoculated bacteria survived poorly following UV-C treatment of apricots.