The influence of water activity and molecular mobility on pectinmethylesterase activity in salt and glucose–maltodextrin model systems

The effect of water activity (aw) and viscosity on the pectinmethylesterase (PME) activity in pectin buffered solutions was investigated. The awmodulation was carried out using two ligands (glucose and sodium chloride) whilst viscosity was changed by adding a thickener (maltodextrin, DE 8.7). The change of “reduced viscosity” due to the addition of substrate, ligands and/or maltodextrin indicated interactions of ligands and thickeners with pectin and among themselves. In ternary systems, the awreduction was the most important factor in the inhibition of PME activity whilst the viscosity increase was less effective. In quaternary systems, at equal awvalues, the increase of viscosity upon maltodextrin addition generally determined an enhancement of the PME activity ascribable to the increase of the “reduced viscosity”. On the basis of the excluded volume theory, this increase determined a crowding effect that positively affects the enzymatic activity. Viscosity and awbeing equal, PME activity was lower in glucose ternary solution than in sodium chloride–maltodextrin quaternary solution despite the lower T'g of the former; this likely due to molecular crowding. The results obtained in this study widen previous knowledge on the effect of aw, viscosity and T'g on the enzymatic activity, highlighting that the relative importance of these factors can largely depend on the type of enzyme, the nature of the components in the system, and their interactions, which, in turn, can increase the enzymatic activity due to macromolecular crowding.