Abstract

The present study aimed to optimize microwave-assisted extraction (MAE) conditions for enhancing the recovery of phenolics, flavonoids, and antioxidant activity from Graptophyllum pictum (L.) Griff. leaves. Response surface methodology (RSM) with an I-optimal design was used to evaluate the effects of solvent-to-solid ratio (10–15 ml/g) and pH (2–6) on total phenolic content (TPC), total flavonoid content (TFC), and antioxidant capacity assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. The experimental runs revealed significant variation among treatments (p < 0.05), with the highest TPC (2.81 ± 0.10 mg GAE/g DW) and DPPH capacity (2.11 ± 0.01 μmol TE/g DW) observed at a ratio of 15:1 and pH 5.92, while the highest TFC (6.50 ± 0.07 mg QE/g DW) and FRAP activity (13.09 ± 0.48 μmol TE/g DW) were recorded at a ratio of 13.25:1 and pH 2.8. The desirability function identified an optimal condition at a ratio of 15:1 and pH 6.0, yielding predicted values of 2.481 mg GAE/g DW (TPC), 6.159 mg QE/g DW (TFC), 2.337 μmol TE/g DW (DPPH), and 13.395 μmol TE/g DW (FRAP), with a desirability score of 0.940, indicating high overall optimization performance. Model validation yielded residual standard errors (RSE) of −6.55% (TPC), 0.54% (TFC), −6.12% (DPPH), and 6.47% (FRAP), all within ±10%, confirming predictive accuracy. These findings indicate that MAE coupled with RSM is a reliable and efficient strategy to maximize bioactive compound recovery from G. pictum leaves, supporting their potential in pharmaceutical and nutraceutical applications.

Key words: Graptophyllum pictum, microwave-assisted extraction, response surface methodology, phenolics, flavonoids, antioxidant activity