Phenolics from Sterculia nobilis Smith pericarp by-products delay carbohydrate digestion by uncompetitively inhibiting α-glucosidase and α-amylase.

Sterculia nobilis Smith pericarp is a by-product of tropical and subtropical fruit Sterculia nobilis Smith, the functional activity and phytochemical composition of which have not been widely reported. In this work, LC-ESI-MS/MS-MRM technique was used for the qualitative and quantitative analysis of 16 phenolic compounds in the ethyl acetate fraction of Sterculia nobilis Smith pericarp extract (EAF). Luteolin-7-O-glucoside, epicatechin gallate and apigetrin were the principal phenolics in the EAF. The hypoglycemic activity of EAF was examined by α-glucosidase and α-amylase inhibition models. EAF inhibited both α-glucosidase and α-amylase activities reversibly and uncompetitively with half-inhibitory concentration (IC 50) values of 69.390 ± 1.410 μg/mL and 2.151 ± 0.044 mg/mL, respectively. Enzyme inhibition mechanism of EAF was studied by spectroscopic methods. The results showed that EAF altered the secondary structure and microenvironment of tyrosine and tryptophan residues of the enzymes. This research demonstrates that Sterculia nobilis Smith pericarp is a potential raw material for production of functional foods at low cost. • Sixteen phenolics were identified in Sterculia nobilis Smith pericarp. • EAF had better inhibitory effects on α-glucosidase than α-amylase. • EAF inhibited both α-glucosidase and α-amylase in uncompetitive manner. • EAF exhibited different fluorescence quenching mechanisms for α-glucosidase and α-amylase. • EAF can decrease postprandial blood sugar levels by delaying the digestion of carbohydrates. [ABSTRACT FROM AUTHOR]