Interaction of Structurally Diverse Phenolic Compounds with Porcine Pancreatic α-Amylase

A blood glucose level lowering effect is postulated for polyphenols (PPs), which is in part attributed to the inhibition of alpha-amylase. To estimate structure-effect relationships, chlorogenic acid (CA), phlorizin (PHL), epigallocatechin gallate (EGCG), epicatechin (EC), and malvidin-3-glucoside (Mlv-3-glc) were used as inhibitors in an enzyme assay, on the basis of the conversion of GalG(2)CNP by alpha-amylase. The detection of CNP was performed by UV/vis spectroscopy. The data reveal that the inhibitor strength decreases as follows: EGCG > Mlv-3-glc > EC > PHL similar to CA. Detection of the substrate conversion by isothermal titration calorimetry supports these results. All PPs showed mixed inhibition, except for CA and EGCG wherein the competitive proportion was predominant. Investigations by saturation transfer difference NMR revealed interaction of PPs with alpha-amylase prevalently based on interactions with the aromatic or conjugated system. A correlation between the extent of the conjugated system and the IC50 of the PP could be found.