Purpose: The objectives of the present study were to examine the efficacy of UV-C in reducing populations of Escherichia coli O157:H7 and Salmonella spp. on apricot fruit, and to evaluate the survival of E. coli O157:H7 and Salmonella spp. during post-UV storage.
Methods: Ultraviolet-C (UV-C, 254 nm, 0-1326 mJ/cm2) light was applied to inactivate 4-5 individual strains of E. 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. The survival of E. coli O157:H7 and Salmonella spp. after exposure to 74 and 442 mJ/cm2 of UV-C were evaluated during post-UV storage at 2 and 20°C.
Results: Results showed that E. coli and Salmonella spp. populations decreased rapidly (1-2 logs) with increasing UV-C doses of 0 to 74 mJ/cm2, which was statistically significant (P < 0.05). Further increases in UV-C dosage achieved only limited additional reductions in bacterial populations. Correspondingly, Shiga toxin-negative bacteria and attenuated S. Typhimurium strains, along with S. Typhimurium LT2, responded similarly to 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 442 mJ/cm2 decreased rapidly at both storage temperatures. After 8 days at 20°C or 21 days at 2°C, 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.
Significance: Our results suggest that surface-inoculated bacteria survived poorly following UV-C treatment of apricots.