Optimization of Flavonoid Extraction and Antioxidant Capacity from Acanthus ilicifolius Using Microwave-Assisted Extraction and I-Optimal Response Surface Methodology

Acanthus ilicifolius is a medicinal plant from the Acanthaceae family commonly found in mangrove forests. Its extract contains antioxidant properties attributed to secondary metabolites, particularly flavonoids. Achieving optimal flavonoid content requires careful consideration of the extraction method. This study focuses on optimizing ethanol concentration and extraction time using I-optimal response surface methodology to maximize total flavonoid content (TFC) and antioxidant capacity in A. ilicifolius leaf extracts. The extraction was performed using varying ethanol concentrations and extraction duration. TFC was measured using a nanospectrophotometer, and antioxidant capacity was evaluated through CUPRAC (cupric ion reducing antioxidant capacity) and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) assays. Statistical analysis identified optimal conditions, with the highest TFC of 0.479 mg GAE/g DW obtained at 69.3% ethanol concentration and an extraction time of 130.2 seconds. Higher ethanol concentrations and longer extraction times generally enhanced flavonoid content and antioxidant activity. The highest antioxidant capacity, as measured by CUPRAC, was achieved at 76.6% ethanol and 138 seconds, yielding 14.149 µmol TE/g DW. The optimized extraction conditions resulted in predicted TFC and antioxidant capacities that closely matched experimental results, demonstrating the accuracy and reliability of the optimization model.