Mechanism of Effect of Caffeic Acid on Terpene Volatility in Wine

Terpenes are typical varietal aroma compounds in wine, and their volatilization and aroma expression are influenced by the matrix effect of phenolic compounds present in wine. Caffeic acid is a representative phenolic acid in wine and can affect the volatilization loss of terpene flavor compounds during wine storage. To elucidate the molecular interaction mechanism between terpenes and caffeic acid, a model wine system containing seven terpenes was prepared. Different concentrations of caffeic acid (0, 62.5, 125, 250, 500, and 750 mg/L) were added, and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry was employed to monitor the changes in terpene concentrations during 90 days of storage at room temperature (25 ℃). Subsequently, sensory analysis was conducted to evaluate the effect of caffeic acid on the olfactory perception of terpenes in wine. Thermodynamic analysis and quantum chemical calculations were performed to investigate the terpene-caffeic acid interaction mechanism from both experimental and theoretical perspectives. Finally, chemical bond disruption experiments were carried out to validate the proposed interaction mechanism. The results showed that caffeic acid suppressed the volatilization of terpenes, with concentrations of 500 mg/L or higher exhibiting the most pronounced effect. After 90 days of storage, the total terpene content in the 750 mg/L caffeic acid treatment group was 113.42% of that in the control group, indicating a significant reduction in volatilization loss. Sensory analysis further corroborated these findings: compared with the control, the 750 mg/L caffeic acid treatment group induced highly significant differences (P < 0.01) in the recognition rates of aroma perception changes for all seven terpenes. Thermodynamic parameters determined by ultraviolet-visible spectroscopy revealed that both ΔH° and ΔS° were positive, indicating that hydrophobic interactions constituted the primary driving force for the non-covalent interaction between terpenes and caffeic acid. In contrast, quantum chemical calculations yielded negative values for ΔH° and ΔS°, suggesting that hydrogen bonding was the key stabilizing factor in terpene-caffeic acid complexes. The chemical bond disruption experiments confirmed the synergistic presence of both hydrophobic interactions and hydrogen bonding in the terpene-caffeic acid system. It was concluded that the addition of caffeic acid at concentrations of 500 mg/L or higher during wine storage could mitigate the volatilization loss of terpenes, and that caffeic acid and terpenes could form stable complexes through hydrophobic interactions and hydrogen bonding. This study was expected to provide technical support and a theoretical basis for the regulation of terpene volatilization and aroma expression in wine, as well as the evaluation of the polyphenolic matrix effect.