Optimizing Polyphenolic Extraction from Wild Guava Leaves: A Response Surface Methodology Approach to Antioxidant and α-Glucosidase Inhibitory Activities

Objective Elevated concentrations of total phenolic content (TPC) and total flavonoid content (TFC) in extracts from wild Psidium guajava L. leaves are associated with their antioxidant and α-glucosidase inhibitory activities. This study aimed to determine the optimal ultrasound-assisted extraction conditions to maximize TPC, TFC yield, as well as antioxidant and α-glucosidase inhibitory potential. Methods The central composite design (CCD) of Response Surface Methodology (RSM) was employed for empirical model development with three levels of factors, including ethanol concentration (33.18 to 66.82% in distilled water), extraction time (1.59 to 18.41 min) and solvent-to-solid ratio (5.79 to 14.20 mL/g). Results The results indicated that under optimal conditions, the total phenolic content (TPC) and total flavonoid content (TFC) values were 152.954 mg GAE/g DW and 113.871 mg QE/g DW, respectively. These conditions included an ethanol concentration of 51.94%, an extraction time of 9.56 min, and a solvent-to-solid ratio (v/w) of 10.84 mL/g. Furthermore, the maximum values for DPPH and ABTS radical scavenging activities were 124.990 mg TE/g DW and 194.730 mg TE/g DW, respectively and the lowest IC 50 for α-glucosidase inhibitory activity recorded at 11.946 µg/mL. The validated models exhibited strong consistency between the predicted and experimental values, with variations of less than 5% under optimal conditions. Additionally, Principal Component Analysis (PCA) also confirmed the appropriate model to predict the extraction yield of total polyphenol and flavonoid content, as well as their biological activities, including DPPH and ABTS radical scavenging and alpha-glucosidase inhibitory activities. Conclusions The enhancement of antioxidant and antidiabetic extraction processes in both the pharmaceutical and food industries through the use of ultrasound-assisted extraction from Wild Guava leaves can increase production to meet high demand. This efficiency is particularly noteworthy, as it demonstrates the advantages of using ultrasound in the extraction process.