Inactivation of Salmonella in steamed fish cake using an in-package combined treatment of cold plasma and ultraviolet-activated zinc oxide

Abstract

An intervention technology combining in-package atmospheric discharge cold plasma (CP) treatment with ultraviolet (UV)-activated zinc oxide (ZnO) treatment was developed to decontaminate steamed fish cakes in commercial plastic packages. Efficacy of the simultaneous treatment of UV-activated ZnO treatment and CP treatment (ZnO&CP treatment) in inactivating Salmonella (1.8 log CFU/g) did not differ significantly from that of the CP-only treatment (P > 0.05). The CP treatment immediately after UV-activated ZnO treatment (ZnO-CP treatment) led to higher inactivation of Salmonella (2.4 log CFU/g) than the ZnO-only (0.4 log CFU/g) or CP-only (1.7 log CFU/g) treatments. Inactivation of Salmonella by ZnO-CP treatment increased as the ZnO or CP treatment time increased, the number of samples in the package decreased, and upon shaking the package during the CP treatment. The difference in Salmonella counts between ZnO-CP treated and untreated samples were maintained at 1.3–1.8 log CFU/g and 1.1–1.6 log CFU/g when samples were stored at 4 °C and 10 °C for 21 days, respectively. The ZnO-CP treatment did not alter the moisture content, water activity, color, pH, and gel strength of the steamed fish cake at both storage temperatures. However, the ZnO-CP treatment reduced the total volatile base nitrogen content in the steamed fish cake stored at 10 °C. These results demonstrated the potential of applying a combined treatment approach for microbial decontamination of steamed fish cake in plastic packages.