Effect of extraction condition on the antioxidant, antiglycation and α-amylase inhibitory activities of Opuntia macrorhiza fruit peels polysaccharides

In this study, the effect of acidic, neutral and alkaline medium extraction of polysaccharides from Opuntia macrorhiza fruit peels was evaluated. The extraction yields ranged from 6.8 to 13.7%, and the highest content in uronic acid was observed in the acidic extract (50.5%). Likewise, Fourier transform infrared (FT-IR) spectroscopy showed the presence of uronic acids in the methyl ester and free forms, with a degree of esterification of 46.9, 39.3 and 48.3% for the acidic, neutral and alkaline extracts. Monosaccharide composition showed that the extracted polysaccharides were principally composed of arabinose, rhamnose, galactose and glucose, with an average molecular weight of 208,000, 1460,000 and 1380,000 g/mol, respectively. Therefore, this finding indicates that extracts are a low methoxyl pectic polysaccharides. Finally, all polysaccharides exhibited good antioxidant activity, especially acid extract significantly inhibits lipid peroxidation and in vitro protein glycation in BSA-glucose glycation model and alkaline extract inhibits α-amylase with a competitive type.