Postharvest UV-C irradiation stimulates the non-enzymatic and enzymatic antioxidant system of ‘Isabel’ hybrid grapes (Vitis labrusca×Vitis vinifera L.)

Ultraviolet light type C (UV-C) was studied as a tool to increase enzymatic and non-enzymatic antioxidant defenses and phytochemical levels in 'Isabel' grapes (Vitis labrusca×Vitis vinifera L.). Grapes were exposed to 0, 0.5, 1.0, 2.0, or 4.0kJm-2 UV-C and stored for 1, 3, or 5days post-treatment. One day after UV-C irradiation, the activities of grape antioxidant enzymes and thiols were increased, especially at 1.0 and 2.0kJm-2. These doses increased total phenolic content by almost 20%, while 0.5 and 4.0kJm-2 had no effects. Total monomeric anthocyanin content was increased by >35% by UV-C at 1.0kJm-2; however, anthocyanin profile was unchanged. Grape skin antioxidant capacity was also improved by UV-C irradiation. The 1.0kJm-2 UV-C was considered the hormetic dose. Postharvest UV-C had an elicitor effect on 'Isabel' grapes, positively impacting the antioxidant capacity and phytochemical content.