•Mechanism study in the interaction of high molecular weight procyanidin and porcine pancreatic α-amylase.•Comprehensive assessment in binding mode and constant of sorghum procyanidins trimer to porcine pancreatic α-amylase.•Secondary structure analysis of porcine pancreatic α-amylase to evaluate the effects of sorghum procyanidins trimer.To examine the mechanisms in the interaction of sorghum procyanidins trimer (SPT) with porcine pancreatic α-amylase (PPA), fluorescence quenching, circular dichroism, and UV spectra methods were adopted. The procyanidins binding mode, binding constant and effect of procyanidins on protein stability and conformation were determined. The fluorescence spectroscopy results showed that the Stern–Volmer quenching constant KSV of SPT on PPA, bimolecular quenching constant kq, and apparent static quenching constant K were 2639.5 M−1, 2.6395 × 1011 M−1 s−1, and 495.19 M−1, respectively. In addition, binding constant KA and number of binding sites were 872.971 M−1 and 1, respectively. Circular dichroism study revealed that PPA conformation was altered by SPT with a major reduction of β-sheet, increase of β-turn, minor change of random coil. UV spectra indicated that SPT influenced the micro-environment of aromatic amino acid residues in PPA. These findings directly elucidate the mechanisms of high molecular weight SPT in interaction with PPA.

Procyanidins are abundant in sorghum episperm. In this study, the effects of procyanidins from Sorghum bicolor (L.) moench episperm (sorghum procyanidins, SPC) in preventing dental caries were investigated through analysis on SPCs’ effects on cariogenic bacteria and ability in scavenging superoxide anion free radicals. In addition, the SPC with activity in preventing dental caries were identified. The ESI-MS/MS analysis results revealed that the compositions of SPC purified by macroporous resin were dimmers, trimers, tetramers, pentamers and hexamers of procyanidins and catechin/epicatechin monomers. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of SPC on Streptococcus mutans (Ingbritt C) and Streptococcus sobrinus 6715 were 8 and 16 mg/ml, respectively. The SPC had a remarkable inhibition effect (P < 0.05) on acid production of S. sobrinus (Ingbritt C) and S. mutans 6715 compared with the control group, and a dose-dependent relationship was observed. By increasing the concentration of SPC in the experimental condition (200–600 mg/L), the scavenging ratio of superoxide anion radicals increased significantly, indicating that SPC could be used as a potential dental-caries-preventative medicine with its antibacterial and antioxidant ability.Research highlights► This study firstly identify the components of procyanidins in sorghum episperm from northern China. ► This study also research the effect of oligomeric procyanidins in sorghum episperm on preventing dental caries in vitro bacteria causing dental caries growth and acid product. ► This study also prove oligomeric procyanidins can scavenge superoxide anion free radical and can be used as a medicine to prevent dental caries or diseases caused by superoxide anion free radical.