Effect of gamma irradiation on inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes on pistachios.

This study evaluated the efficacy of gamma irradiation to inactivate food-borne pathogens on pistachios (Pistacia vera L.). Pistachios inoculated with Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes were subjected to gamma irradiation in the range of 0, 0·5, 1, 3 and 5 kGy, and colour change was evaluated after treatment and during storage at room temperature. Pathogen populations decreased with increasing treatment doses. A gamma irradiation dose of 5 kGy decreased the three pathogens on pistachios to under the detection limit (1·0 log CFU per g) without effecting colour change. During storage following treatment, pathogens were reduced due to the postirradiation effect. D-values of pathogens on pistachios showed that L. monocytogenes was more resistant to gamma irradiation than was E. coli O157:H7 or S. Typhimurium. During gamma irradiation treatment, L, a and b values of pistachios did not significantly change but these values changed during storage. These results show that gamma irradiation has potential as a nonthermal process for inactivating food-borne pathogens in pistachios without inducing colour changes. SIGNIFICANCE AND IMPACT OF THE STUDY: Generally, nuts have lower water activity which precludes the growth of food-borne pathogens. But, food-borne outbreaks due to pathogen-contaminated nuts have been reported in the last few decades. Pistachios are one of the most popular nuts and have many health beneficial effects. However, many pasteurization interventions have been used to reduce pathogens on pistachios, but most of them are not effective. This study confirms the effectiveness of gamma irradiation on pasteurization of pistachios. This may be helpful in nut processing industries to ensure the microbial safety of nuts.