Optimizing solvent composition for enhanced extraction of phenolic content and antioxidant activity from Coleus scutellarioides through I-optimal mixture design

Background: Reactive oxygen species are unstable molecules that contribute to oxidative stress and are associated with numerous degenerative diseases. The leaves of Coleus scutellarioides are rich in phenolic and flavonoid compounds, which possess strong antioxidant properties.Objectives: This study aimed to optimize the composition of water, ethanol, and methanol as solvents using the I-optimal mixture design to enhance the extraction of total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, and ferric reducing antioxidant power (FRAP).Methods: Each extraction was performed by macerating 1 g of powdered C. scutellarioides leaves in 20 mL of the designated solvent mixture. The maceration process was conducted at 25°C for 24 h with intermittent stirring. After extraction, the mixture was filtered, and the filtrate was analyzed for TPC, DPPH radical scavenging activity, and FRAP. Raw data were processed using Microsoft Excel, and Design-Expert software (version 13) was used for model fitting and optimization. Model performance was evaluated using contour plots and numerical optimization, and verification was performed using relative standard error (RSE), where values below 10% indicate good predictive accuracy.Results: The highest TPC (25.74 mg gallic acid equivalent/g dry weight) was obtained using 21.79% water and 78.21% methanol. The strongest DPPH scavenging activity (5.107 μmol trolox equivalents [TE]/g dry weight) was observed with 100% methanol, while the highest FRAP (228.267 μmol TE/g dry weight) was achieved using 49.73% water and 50.27% ethanol. The optimal solvent composition was identified as 26.02% water and 73.98% methanol, with a desirability value of 0.938. Model validation showed that all response variables had RSE values below 10%, confirming the model’s strong predictive performance.Conclusion: These findings highlight the importance of solvent selection in optimizing antioxidant extraction from C. scutellarioides, offering valuable guidance for efficient phytochemical extraction from medicinal plants.