Response Surface Methodology Applied to the Optimization of the Preparation of Antioxidant and Antidiabetic Extracts from Phragmanthera capitata (Spreng.) Balle: Effect of Particle Size, Powder-to-Solvent Ratio, and Temperature

Phragmanthera capitata is a medicinal plant used in traditional medicine to treat several diseases, including diabetes. Its antioxidant properties and inhibitory effects on enzyme-carbohydrate digestion activities have been demonstrated. The present study aimed to provide data that can contribute to rationalizing the preparation of antioxidant and antidiabetic extracts from this plant. P. capitata (whole plant) growing on Persea americana was harvested at the fruiting stage. A response surface design-type central composite was applied to maximize the extraction yield, phenolic contents, and antioxidant and antidiabetic properties of the ethyl acetate extract of P. capitata. The influencing extraction factors were temperature, powder particle size, and solvent-to-powder ratio. The total phenolic content, total antioxidant capacity (TAC), DPPH scavenging ability, ferric reducing antioxidant power (FRAP), and antidiabetic (α-amylase and α-glucosidase inhibitory) effects of the extracts were determined using conventional methods. A temperature above 55°C contributed to the degradation of the extract, which was reflected in the GC-MS profile by a significant reduction in the number of compounds it contained. The optimal conditions were defined as 24.42°C for temperature, 250 µm powder particle size, and 8.30 (v:w) solvent-to-powder ratio. This extraction protocol resulted in more than twice the extraction yield (3.05%), TTC (62.30 mg TAE/g), TAC (41.41 mg AAE/g), FRAP (186.56 mg AAE/g), and α-amylase (IC(50) 15.05 µg/mL) and α-glucosidase (IC(50) 21.14 µg/mL) inhibitory activities compared to our previous results. Additionally, these optimal conditions led experimentally to the extraction of higher phenolic content and to the attainment of higher antioxidant and antidiabetic activity, which closely matched the predicted values. Using these conditions, it is possible to prepare an antidiabetic phytomedicine from P. capitatathat can prevent oxidative stress complications. However, further complementary studies should be carried out considering other factors that influence the composition and pharmacological properties of the extract.