Title: Fate of E. coli O157:H7, Salmonella spp. and potential surrogate bacteria on apricot fruit following UV-C light Authors
Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 2013
Publication Date: August 3, 2013
Citation: Yun, J., Yan, R., Fan, X., Gurtler, J., Phillips, J.G. 2013. Fate of E. coli O157:H7, Salmonella spp. and potential surrogate bacteria on apricot fruit following UV-C light. International Journal of Food Microbiology. 166:356-363. Interpretive Summary: Some fruit growers/packers market high maturity fruit to satisfy consumer’s increasing demand for high quality fruit. However, these so-called “tree ripe” fruits can not be washed with aqueous sanitizers due to their softness. To minimize the risk of human pathogens on this type of fruit, non-aqueous technologies are needed. This research investigated the efficacy of ultraviolet (UV) C light in reducing population of two human pathogenic bacteria on apricot and the survival of the bacteria during post-UV storage. Results suggest that UV-C reduced the population of bacteria by up to 99.6% and the bacteria survived poorly on apricots following UV treatment. Therefore, this simple technology may be used by the fruit industry to enhance the microbial safety of soft fruits.
Technical Abstract: 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 S. Typhimurium LT2. Also, the survival of E. coli O157:H7 and Salmonella spp. after exposure to 74 and 442 mJ/cm2 of UV-C was evaluated during post-UV storage at 2 and 20C. The fruit were spot inoculated and the areas (ca. 1.5 cm2) of fruit surface with the inoculated bacteria were exposed to UV-C at 7.4 mW/cm2. E. coli O157:H7 and Salmonella spp. populations decreased rapidly (1-2 logs) (P less than 0.05) with increasing UV-C doses of 0 to 74 mJ/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 20C, populations of pathogenic E. coli O157:H7 and Salmonella spp. on untreated fruit decreased slowly; however, populations on fruit treated with 442 mJ/cm2 decreased rapidly at both temperatures. After 8 days at 20C or 21 days at 2C, E. coli O157:H7 and Salmonella spp. populations on UV-C treated fruit were at least 2 log CFU/g lower than on non-treated controls. Our results suggest that surface-inoculated bacteria survived poorly following UV-C treatment of apricots.