Responses of phytonutrients and tissue condition in persimmon and cucumber to postharvest UV-C irradiation

Postharvest UV-C irradiation is expected to be a widely applicable sterilization technology for fruit and vegetables. In this study, the effects of UV-C irradiation on phytonutrients and tissue conditions in persimmon and cucumber were investigated. UV-C having a peak wavelength of 253.7 nm was irradiated on their surface (12.9 W m(-2)) for 0 to 15 min. The UV-C irradiation was not effective for the enhancement of phytonutrients (polyphenol, beta-carotene, ascorbic acid, chlorophyll) in persimmon and cucumber. However, some responses of tissue condition to UV-C irradiation appeared. Some persimmon fruit became blackened during storage, and the transfer of tannin from the parenchyma to the epidermal tissue was observed in the fruit. We also evaluated the factors responsible for the color change in the fruits. In addition, electrical impedance was measured, and electrical properties were obtained by equivalent circuit analysis. These properties reflected the tissue conditions. In particular, the extracellular resistance of UV-C-irradiated cucumber exhibited clear differences from non-irradiated samples.