Interactions between polyphenols in thinned young apples and porcine pancreatic α-amylase: Inhibition, detailed kinetics and fluorescence quenching

• Total and individual polyphenols in young apples were studied for their inhibition against amylase.
• Real (maize) starch granules were used and observed to analyse α-amylase inhibition.
• Dixon and Cornish-Bowden plots were used to determine inhibition constants (Kic, Kiu).
• Fluorescence quenching of α-amylase by polyphenols in thinned young apples were analysed.
• The correlation of IC50, competitive inhibition constant and quenching constant was discussed.

Young apple polyphenols (YAP) and nine types of phenolic compounds were investigated regarding the inhibitory activity against porcine pancreatic α-amylase (PPA) in vitro. Tannic acid, chlorogenic acid and caffeic acid in YAP showed relatively high inhibition with the IC50 values of 0.30, 1.96 and 3.69 mg/mL, respectively. A detailed kinetics of inhibition study revealed that YAP and tannic acid were competitive inhibitors of PPA, whereas chlorogenic acid and caffeic acid were mixed inhibitors, exhibiting both competitive and uncompetitive characteristics. The fluorescence of PPA could be significantly quenched by YAP and the three polyphenols, and their quenching constants were determined. The results showed that for the polyphenols investigated, the order of the apparent static quenching constants (KFQ) was in agreement with that of the reciprocal competitive inhibition constants (1/Kic) (tannic acid > chlorogenic acid > caffeic acid > epicatechin); both of the parameters were contrary to the order of the IC50 values. Thus, combining detailed kinetics and fluorescence quenching studies can be applied to characterise the interactions between polyphenols in young apples and α-amylase.