Systematic NMR-based determination of Gallic Acid as a putative marker that reflects the impact of oenological practices

Gallic acid is one of the most important phenolic acids in wine, contributing to oxidative stability, copigmentation and organoleptic properties. This study maps concentration variations of this compound and evaluates it as a putative marker reflecting the cumulative impact of winemaking practices using Nuclear Magnetic Resonance (NMR) spectroscopy. A total of 277 wine samples was analyzed, focusing on emblematic indigenous varieties from Greece (Agiorgitiko, Xinomavro, Assyrtiko, Moschofilero) and Cyprus (Mavro, Maratheftiko, Xynisteri), alongside selected international varieties. The dataset was stratified into commercial and non-commercial experimental vinifications. Identification was confirmed by 2D NMR and spiking experiments. Statistical analysis revealed a clear distinction between baseline varietal potential and the impact of oenological practices. In non-commercial red vinifications, gallic acid ranged from 47.37-146.28 mg/L (Agiorgitiko) and 38.65-133.49 mg/L (Xinomavro), while commercial samples extended up to 409.97 mg/L and 197.14 mg/L, respectively. In white wines, non-commercial baselines were up to 18.94 mg/L (Assyrtiko) and 11.19 mg/L (Moschofilero), whereas commercial wines ranged up to 201.26 mg/L and 88.06 mg/L, respectively. These differences relate to practices like oak barrel use, maceration intensity and aging. Overall, this NMR approach highlights gallic acid as a putative marker for evaluating oenological practices and phenolic evolution.