Extracting citrus peel-derived polyphenols using hydrophobic deep eutectic solvents: Mechanism, optimization, and bioactivity evaluation

This study optimized hydrophobic deep eutectic solvent (HES) extraction of citrus peel polyphenols. Thymol-camphor-based HES (molar ratio of 1:1) showed a higher total polyphenol content (TPC) than other HESs. FTIR and 1 H NMR confirmed the formation of HES. Conductor-like screening model for real solvents (COSMO-RS) calculations indicated the relatively low viscosity/density of the HES and revealed synergistic extraction mechanisms (hydrogen bonding, hydrophobic interaction, and van der Waals force). The TPC of HES extract is about 2.78 % and 9.57 times higher than that of ethyl acetate and choline chloride-ethylene glycol-based deep eutectic solvent extract, respectively. The 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) free radical scavenging rate and ferric reducing antioxidant power (FRAP) of extract are 96.98 % and 152 % of that of vitamin C at the same concentration, respectively. The inhibition rate of the extract on α-glucosidase and α-amylase activity are respectively 92.27 % and 210 % of that of acarbose at the same concentration. The extract exhibited potent antioxidant and hypoglycemic activity.