Radiosensitivity of Feline Calicivirus F9 on Iceberg Lettuce Surface after Combined Treatments with γ-Radiation

Abstract

The surface of iceberg lettuce (Lactuca sativa L.) is favorable to the survival of pathogens such as bacteria, parasites, and viruses such as norovirus. The present study was conducted to investigate the antiviral properties of treatment with cranberry juice (CJ), ozone (O3), and γ-radiation alone or in combination against feline calicivirus (FCV) F9 present on the surface of iceberg lettuce. The lettuce leaves were inoculated with virus suspensions at ∼6 log TCID50 (50% tissue culture infective dose)/mL and treated with CJ, O3, and γ-radiation alone and in combination during storage at 4°C. The D10-values of 1.21 kGy, 2.23% CJ, and 14.93 ppm of O3 were obtained when samples were treated with various radiation doses, CJ, and O3, respectively. Relative radiosensitization of FCV-F9 virus on lettuce was 1.20, 1.50, 1.09, and 1.00 after combined CJ treatments of 0.1, 0.25, 0.50, and 1.50%, respectively. Optimum treatments were 5 ppm for 7.5 min for O3, 0.25% CJ, and γ-radiation at 1.5 kGy when each treatment was used alone. The combination of the three treatments produced the highest reduction of 2.15 log TCID50/mL (from initial inoculation of ∼7 log TCID50/mL) during 10 days of storage at 4°C. Antibacterial properties of treatments and physicochemical quality of lettuce were investigated during 13 days of storage at 4°C. The treatment of lettuce with γ-radiation alone (1.5 kGy) reduced the total flora by 3 log CFU/g; however, the combination of CJ (0.25%) with irradiation (1.5 kGy) reduced it by ∼5 log CFU/g after 13 days of storage at 4°C. The texture and color of the lettuce treated with the combined treatments changed slightly during storage, and chlorophyll increased by 3.81 μg/mL after 10 days of storage at 4°C. Significant differences in taste and color were observed in lettuce without treatments after 5 days of storage, whereas no difference was observed after the 0.25% CJ or the combined treatments.