Comparison of enzymatic de-esterification of strawberry and apple pectin at elevated pressure by fungal pectinmethylesterase

Water soluble pectin was isolated from strawberries. Sugar composition, degree of esterification and molar mass were compared with commercial apple pectin. Both pectins were subjected to enzymatic de-esterification by recombinant Aspergillus aculeatus pectinmethylesterase (PME). Rate of enzymatic de-esterification at elevated pressures (0.1–500 MPa) and temperatures (20–60 °C) was assayed by measuring the release of methanol as a function of time. Optimal activity was observed at 200–300 MPa combined with 45–55 °C. At all conditions investigated, both pectins were de-esterified at similar initial rates. However, after prolonged enzymatic treatment at atmospheric pressure and 30 °C, apple pectin was de-esterified to a significantly lower degree of esterification (7%) than strawberry pectin (32%). The mode of action of A. aculeatus PME was investigated by enzymatic fingerprinting of de-esterified pectin chains. The enzyme de-esterified according to a “multiple chain, multiple attack” mechanism, irrespective of the substrate.status: publishe