A novel hydrogen-incorporated carbon dioxide supercritical system for extracting phytochemicals from grape peels: Response surface methodology–based modeling and optimization

• Sp-CO₂-H₂ method enables selective enrichment of phytochemicals rather than solely increasing total phenolic content (TPC) • The highest TPC (33.75 mg GAE/100 mL), DPPH (62.02%), and ABTS (65.47%) were obtained at 80 bar, 60 °C, and 5 min • Moderate RSM model performance can still provide reliable optimization outcomes in complex multi-response extraction systems • Multivariate analyses reveal a consistent decoupling between total phenolic content and antioxidant activity • PCA and correlation patterns support selective extraction behavior under optimized Sp-CO₂–H₂ conditions • Sp-CO₂–H₂ increased the TPC, DPPH, and ABTS of extracts by 55%, 44%, and 24%, respectively, compared to the classical Sp-CO 2 method The supercritical hydrogen-incorporated carbon dioxide (Sp-CO 2 –H 2 ) extraction was evaluated as a hybrid solvent system for the recovery of phytochemicals from grape peels, utilizing response surface methodology (RSM), mathematical modelling, and optimization techniques. The independent variables (pressure, temperature, and time) were optimized using RSM for total phenolic content (TPC), antioxidant activity, and individual phenolic compound levels. The optimum Sp-CO 2 –H 2 conditions were determined as 80 bar, 60 °C, and 5 min. The developed RSM models showed acceptable performance, with coefficients of determination (R²) ranging from moderate to high values and statistically significant model terms (P