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

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.