Synergistic Effect and Mechanisms of Combining Ultrasound and Pectinase on Pectin Hydrolysis

Abstract

The current study aimed to investigate the synergistic effect of ultrasound and pectinase on pectin hydrolysis. Effects of ultrasound on the hydrolysis rate of pectin, enzymatic kinetics parameters and pectinase structures (determined by the DNS method, Michaelis–Menten equation, chemical reaction kinetics model, fluorescence spectroscopy and circular dichroism spectroscopy) were also studied in order to illuminate the mechanisms of the synergistic effect. The hydrolysis rate of pectin achieved maximum value with ultrasound treatment at 4.5 W mL−1 intensity and ultrasound time of 10 min, increasing by 32.59 % over the control. The optimum temperature for the hydrolysis reaction was 50 °C and kept unchanged with ultrasound treatment. Besides, the value of V max increased whereas K m decreased in the sonoenzymolysis reaction compared with that in the routine enzymolysis reaction. Results indicated that under ultrasound irradiation, pectin was hydrolyzed at an elevated rate and the pectinase exhibited stronger affinity to the substrate. Fluorescence spectra revealed that ultrasound favorably decreased the amount of tryptophan on the pectinase surface; while the far-UV circular dichroism spectra showed an increased fraction of β-sheet and a reduced fraction of random coil in the secondary conformation. Changes in the pectinase structures contributed to the enhancement of pectinase activity and the consequent promotion of the hydrolysis process. Results of pectin degradation kinetics certified the synergistic effect of ultrasound and pectinase at the temperature range of 20–50 °C, which were evidenced from the positive values of the synergistic coefficients.