Quantitative description and microscopic mechanism of ginsenosides' reactions during the thermal-driven processing of...

P. ginseng is prized for its nutritional and medicinal properties, primarily due to the presence of ginsenosides. During thermal processing, ginsenosides undergo complex chemical reactions, including hydrolysis and elimination, generating rare ginsenosides with enhanced bioactivity. Deciphering these reaction patterns and mechanisms is crucial for optimizing processing techniques.

P. ginseng samples were processed at various temperatures and for different durations, and ginsenoside content was analyzed using UPLC. Thermodynamic parameters were calculated using Gaussian software, and molecular mechanics and frontier orbital theories were applied to predict reaction sites and explore mechanisms. Simulated reactions of reference solutions were used to verify the quantitative rules.

Significant variations in ginsenoside content were observed across different temperatures and durations. Rb1 transformation peaks under moderate heat, selectively forming Rg5. Rg1 was readily transformed, producing Rh4 under harsh conditions and Rk3 under mild ones, allowing for product-specific tuning. Thermodynamic calculations revealed that most reactions had negative Gibbs free energy changes (ΔG), indicating spontaneity, with ΔG decreasing at higher temperatures. The HOMO-LUMO energy gaps of ginsenosides were less than 0.4, indicating high ginsenoside reactivity, and the energy difference between the LUMO of ginsenosides and the HOMO of H₂O influenced hydrolysis reaction rates.

This study provides valuable insights into the chemical reaction patterns of ginsenosides during thermal processing. Temperature significantly impacts reaction direction, extent, and product selectivity. The findings establish a mechanistic foundation for optimizing P. ginseng processing conditions to achieve the desired ginsenoside profiles.