Combined effect of sodium hypochlorite and gamma-irradiation for the control of Vibrio vulnificus in fresh oyster and clam

Abstract

This study investigated the synergistic bactericidal effects of treatment with a combination of sodium hypochlorite (NaOCl) and gamma irradiation against Vibrio vulnificus on shucked oysters and clams. The V. vulnificus population decreased to 1.1–4.8 and 1.2–4.8 log10 colony forming units/g in oysters and clams, respectively, after treatment with a combination of NaOCl (20–80 ppm) and gamma irradiation (0.1–2.0 kGy). V. vulnificus was not detected on oysters or clams after exposure to 60–80 ppm NaOCl and then 2.0 kGy gamma irradiation, where a >2-log synergistic reduction in bacterial population was observed. Based on the Weibull model, 5D-values for 5-log reductions were calculated for treatment with 60 ppm NaOCl with 1.1 kGy irradiation and 80 ppm NaOCl with 0.9–1.0 kGy gamma irradiation. These results indicate treating V. vulnificus populations 5 logs in size with a combination of 60 or 80 ppm NaOCl and 0.9–1.1 kGy gamma irradiation could be a strategy used in post-harvest processing of seafood and distribution to enhance the microbial safety of molluscan shellfish.