UV-C Enhances Phenolics Metabolism and the Production of the Related Bioactive Compounds in Green Chi-fah Chili (Capsicum annuum L. cv. Chi-fah Kiaw) Fruit

Abstract

One of the fruit vegetables that is a favorite for consumers of spicy food worldwide is chili (Capsicum annuum). Thus, the external and internal quality attributes of harvested chili fruit, such as peel color and fruit antioxidants, are of interest for different cooking needs. UV-C is the shortest wavelength of ultraviolet radiation that can harm the living organisms. However, short-term exposure to this physical stress might have many advantages for crop species. This research studied the post-harvest effect of UV-C exposure for different times (0, 10, and 20 min) on the green fruit of Chi-fah chili. The results showed that the percentage of fruit with red peel color increased rapidly during storage after UV-C irradiation, especially in the 10-minute treatment 75% of fruit had red color after 6 days. UV-C treatment also promoted phenolic biosynthesis in green Chi-fah chili fruit as 10 and 20 min of UV-C exposure elevated phenolic contents in both the pulp and placenta with the maximum of 30 and 45 mg gallic acid/gFW, respectively. Exposure to 20 min of UV-C irradiation seemed to inhibit flavonoid production, whereas 10 min UV-C irradiation increased flavonoids in both the pulp and placenta (0.72 and 0.87 mg rutin/gFW, respectively). Of particular interest to the consumers, UV-C treatment could increase the capsaicin amount in green Chi-fah chili fruit. Only the fruit irradiated with UV-C for 10 min had the highest level of phenylalanine ammonia-lyase (PAL) activity in the pulp one day after storage, while the placenta had the highest level of PAL activity from day 1 to day 3. The 10 and 20 min UV-C irradiation led to the highest peroxidase (POD) activity in the pulp and the placenta, respectively. In conclusion, UV-C could be used to enhance the production of phenolics and related bioactive compounds, such as flavonoids and capsaicin in green Chi-fah chili fruit during postharvest storage.