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Resveratrol and its glucoside, piceid, are the primary stilbenes present in wine. These compounds are well known for their pharmaceutical properties. However, these compounds can undergo chemical transformations in wines, such as polymerization in the presence of metallic reagents. This study investigates the oxidative coupling of resveratrol and piceid to form dimers, including δ-viniferin and δ-viniferin-diglucoside. These dimers were synthesized using silver acetate. The formation of these stilbenes was monitored in wine model solutions and red wines. The results indicated that resveratrol and piceid underwent transformation during heat treatment, forming their respective dimers. The polymerization of both compounds is temperature-dependent, with higher conversion rates at elevated temperatures. Notably, piceid was more reactive than resveratrol in wine. Finally, the anti-inflammatory effects of these compounds were evaluated on the RAW 264.7 macrophage cell line. [ABSTRACT FROM AUTHOR]

BACKGROUND: Stilbenoid extracts, such as those originating from grapevine by‐products (e.g. canes), are of interest for use as biopesticides in vineyard owing to their antimicrobial activities. However, stilbenoids are unstable in the environment, especially under light. This study aimed to chemically characterize the effect of UV light on stilbenoids present in a grapevine cane extract (CE), and to evaluate the antimicrobial activities against two major grapevine pathogens (Plasmopara viticola and Botrytis cinerea) of grapevine extracts exposed to UV. RESULTS: Treatment with UV (365 nm) on a grapevine CE led to degradation of stilbenoids (up to 71% after 1 h). The stilbenoid stability depended on their chemical structure: only those possessing CC, as trans‐resveratrol and trans‐ε‐viniferin, were affected with first their isomerization and secondly their oxidation/cyclization. As a consequence, UV‐exposed extracts (UV‐CEs) showed reduced antimicrobial activities against the two pathogens (mycelium and spores). For instance, regarding P. viticola, an UV‐CE exposed during 4 h showed an almost total loss of its activity on oomycete development and a 2.4‐fold inhibition of zoospore mobility in comparison to CE. For B. cinerea, the inhibition capacity of the same UV‐CE was reduced by only 1.1‐fold on mycelial development and by 3.2‐fold on conidial germination compared to CE. CONCLUSION: UV light triggered modifications on the structure of bioactive stilbenoids, resulting in losses of their antimicrobial activities. Photoprotection of stilbenoids has to be considered in the perspective of using them in vineyards as biopesticides. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]