Creation and Functional Evaluation of a Novel Antioxidant Compound via UV-Induced Structural Transformation of Epicatechin from White Wine Pomace

Plant-derived polyphenols, particularly flavonoids, have attracted considerable attention for their antioxidant activity and their potential to prevent aging and lifestyle-related diseases. White wine pomace, a winemaking byproduct, contains abundant nonpigmented polyphenols; however, most remain unutilized and are typically discarded. Herein, epicatechin (EC), a major flavonoid in white wine pomace, was irradiated with ultraviolet (UV) light at 302 nm, producing a novel compound, designated as compound X. Compound X was isolated and purified by preparative high-performance liquid chromatography (HPLC). Structural characterization using nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and mass spectrometry (MS) revealed a bicyclo[2.2.2]-octane-type skeleton featuring an intramolecular C-C bond between the A and B rings and a ketone group at the C-5 position. Electron spin resonance (ESR) analysis showed that compound X had substantially stronger hydroxyl radical (^·OH)-scavenging activity than epigallocatechin gallate (EGCg, IC₅₀ = 395.9 μM), vitamin C (IC₅₀ = 1327 μM), Trolox (IC₅₀ = 1436 μM), and EC (IC₅₀ = 2755 μM), with an IC₅₀ of 71.42 μM. In all five pomace samples tested, a peak corresponding to compound X (<i>m</i>/<i>z</i> 289.0712) was observed following UV irradiation, confirming conversion of flavan-3-ols such as EC into compound X. These results highlight the potential to generate high-value bioactive compounds from white wine pomace via photoinduced structural modification, offering a sustainable approach for valorizing underutilized agro-industrial resources.