Effect of postharvest UV-B or UV-C irradiation on phenolic compounds and their transcription of phenolic biosynthetic genes of table grapes.

Ultraviolet (UV) irradiation has been related to the extension shelf-life and maintenance of postharvest quality in fruits. However, the comparison of UV-B and UV-C treatment on the biosynthesis of phenolic compounds of grape remain unclear. This study provides a comparison on the mechanism of phenolic secondary metabolism at the same dose of 3.6 kJ m-2 UV treatment. Total phenolic compounds, total flavonoid, total flavanol, and total anthocyanin content and antioxidant activities of grapes after UV-C treatments were higher than those of the control and UV-B treatment. Among the evaluated parameters of individual phenolic compounds, the content of trans-resveratrol showed the highest percentage increase after the UV application. The transcriptions of PAL, CHS, F3H, LAR, ANS and STS were higher in grapes treated by UV-C than in those treated by UV-B. The CHS, LAR, ANS and STS genes were more induced in UV-B treatment than in control group. The same applied dose of UV-B or UV-C irradiation have different impact on gene expression and phenolic metabolites synthesis. The UV-C irradiation stimulated a higher gene expression of the phenolic compounds biosynthesis and also induced a greater accumulation of these metabolites at the same applied dose.