Abstract: The extraction of bound phenolics from fresh lotus seeds from Jianning was optimized using a central composite design. Optimization experiments were carried out by investigating the effect of solvent pH, alkali concentration, solid-to-solvent ratio and extraction time on extraction efficiency. The extract was fractionated with solvents of different polarities and the resulting fractions were comparatively evaluated for their antioxidant activity by total antioxidant capacity, 1,1-diphenyl-2-picrylhydrazyl (DPPH), and hydroxyl radical scavenging assays. The results showed that the optimum extraction conditions were determined as follows: NaOH concentration, 2.8 mol/L; solid-to-solvent ratio, 1:25 (g/mL); and extraction time, 3.7 h. Under these conditions the yield of bound phenolics was (8.483 ± 0.063) mg/g of dry matter. In addition, all the fractions possessed high total antioxidant capacity, DPPH and hydroxyl radical scavenging capacity in a dose-dependent manner. Among these, ethyl acetate and n-butanol fractions showed higher antioxidant activity. In conclusion, fresh lotus seeds contained abundant bound phenolics and the ethyl acetate and n-butanol fractions exhibited higher antioxidant capacity.

Key words: fresh lotus seed, bound polyphenols, central composite design, antioxidant activity