Comparison of ozone and UV-C treatments on the postharvest stilbenoid monomer, dimer, and trimer induction in var. 'Superior' white table grapes

Postharvest treatment of seedless white table grapes (var. `Superior') with different gas ozone concentrations (3.88 and 1.67 g/h) for 1, 3, and 5 h induced an increase in stilbenoid biosynthesis [trans-resveratrol, piceatannol, and viniferinas (resveratrol dehydrodimers and dehydrotrimers)] during storage at 22 degrees C and 95% relative humidity. The maximal resveratrol concentration was reached after 2 days of storage, and this amount was similar to that induced by optimized UV-C treatments (1 min, 510 W, 40 cm). Although similar resveratrol concentrations accumulated in grapes after both UV-C and O-3 treatments (maximum ozone production and time), the ozone treatment was more efficient in inducing viniferins accumulation in grape berries. A sequence in the biosynthesis of stilbenoids was observed, starting with the resveratrol monomer, continuing with the resveratrol dehydrodimers epsilon-viniferin and delta-viniferin, and ending with four different resveratrol dehydrotrimers. These trimers were different from alpha-viniferin, a trimer previously reported to be induced in grapes after biotic and abiotic stresses. Two alpha-viniferin isomers were also detected in the ozone-treated grapes, although at very low concentrations that prevented their quantification.