Daily Preharvest UV-C Light Maintains the High Stilbenoid Concentration in Grapes.

The fact that it is possible to induce stilbenoid synthesis in grapevine (Vitis vinifera) by UV-C light allows the possibility of stimulating grapevine phytoalexin production to increase disease resistance and immunity, and subsequently to limit the use of pesticides in vineyards. UV-C light was applied daily during three days before the harvesting of table grape variety Crimson seedless to study the accumulation of stilbenoid compounds during ripeness. The E-resveratrol concentration was monitored during daily preharvest UV-C light application and compared with that after a single application. Daily periodic preharvest UV-C light treatment showed a cumulative effect on grape stilbenoids. An 86-fold stilbenoid level increase (sum of E-resveratrol, E-piceatannol, ε-viniferin, E-piceid, isorhapontigenin, ω-viniferin, and Z-piceid) in grapes was achieved. The effects of UV-C light on stilbenoid in grape cane was also addressed for the first time. Stilbenoid oligomers such as hopeaphenol, ampelopsin A, and r-viniferin were quantified in cane samples. Quality grape parameters indicated an acceleration of ripening in UV-C samples.