Optimization and kinetics of polyphenol recovery from raw mango (Mangifera indica L.) peel using a glycerol-sodium acetate deep eutectic solvent system

Microwave-assisted extraction is a potential clean-energy technology processing raw materials like mango peel into bioactive polyphenolic compounds and using residues as bioenergy (biofuels, heat, and electricity). Mango fruit has been reported as a source of bioactive compounds, although information about their peel is very limited. Generally peels are not used for any commercial purposes, which create a major waste disposal problem, thereby, contributing to pollution. Mangiferin is the main polyphenol in the mango peel in terms of antioxidative capacity. Deep eutectic solvents (DESs) are fast emerging green extractants. The present investigation intends to develop microwave-assisted deep eutectic solvent extraction (MADESE) for recovering polyphenolic antioxidants from mango peels. Glycerol:sodium acetate (Gly:SA) provided the highest TPC from mango peel among all the investigated DES systems. In order to evaluate the interactive effects of the three most relevant operating variables, the Box–Behnken design (BBD) matrix and response surface methodology (RSM) were used in the experimental design. The effects of microwave power (150–450 W), time (10–20 min), and liquid to solid ratio (40–60 mLg⁻¹) on TPC of raw mango peels were examined in this study. Most favorable conditions for MADESE were planned by BBD layout, which consisted of 20% water in Gly:SA (3:1, mol/mol) as the extraction solvent, microwave power (440.18 W), time (12.10 min), and liquid to solid ratio (59.99 mLg⁻¹). By employing optimized conditions, recovery of TPC obtained was 155.28 mg GAE g⁻¹ dw, which was higher than other organic solvents like distilled water or 70% (v/v) methanol. Kinetics study revealed that the extraction rate was very slow for Gly:SA DES system due to their higher viscosity. Thus, MADESE-based extraction methods can be applied for extracting bioactive compounds from biomass at industrial level, which has major applications in the areas of food and medicine.