α-amylase is a key enzyme in the production of beer due to the breakdown of starch into fermentable sugars. During the preparation of the brewing mash, the enzyme can be affected by polyphenols present in the mixture. Our aim was to evaluate the kinetics and equilibrium of the interaction of α-amylase with some polyphenols (chlorogenic, caffeic, ferulic acids and quercetin) present in beer in the usual range of mashing temperatures (40 - 80 °C), and to treat the results with integrated Michaelis-Menten and Stern-Volmer equations. The results showed a competitive inhibition model for all compounds with Ki values around 30 umol.L-1. The binding constants (Kb) revealed increasing values with temperature up to 323 K, corroborating the enzymatic data. Values for ΔH and ΔS revealed an entropy-driven association mechanism. Structure-activity relationships demonstrated a positive correlation between the biological activity of α-amylase and the polar nature descriptors of the polyphenols. Binding assays of the enzyme with chlorogenic acid at different pH and ionic strength support the structure-activity and thermodynamic data and suggest a plausible interaction of the carboxylate ion of the ligand with basic groups in the vicinity of the catalytic site of the enzyme.
Keywords:
α-amylase; polyphenols; binding; kinetic; beer
