Degradation kinetics and structural characteristics of pectin under simultaneous sonochemical-enzymatic functions

• Mild ultrasound enhanced the enzymatic degradation of the pectin molecular weight.
• Degradation of the pectin molecular weight fitted the second-order kinetics.
• The degree of methoxylation of the sonoenzymolysis pectin significantly decreased.
• The sono-enzymatic reaction severely degraded pectin’s homogalacturonan regions.

This study investigated the degradation kinetics and structural properties of pectin with combining ultrasound and pectinase treatment. Ultrasound at an intensity of 4.5 W mL−1 and a time of 10 min significantly enhanced the enzymatic degradation of pectin weight-average molecular weight (MwMw). The degradation kinetics model of pectin followed 1/Mwt−1/Mw0=kt1/Mwt−1/Mw0=kt, suggesting the randomness of the degradation process. Synergistic effects of ultrasound and pectinase were observed at 20–60 °C and were more effective at lower temperatures. Furthermore, the degree of methoxylation (DM) of sonoenzymolysis pectin significantly decreased whereas the degree of acetylation (DAc) remained unchanged compared to the original and enzymolysis pectin. Simultaneous functions of ultrasound and pectinase caused severe decomposition in pectin homogalacturonan (HG) regions without altering the monosaccharides types, configurations and glycoside linkages of the pectin samples. The complex polymeric structures of pectin transformed into smaller units with simpler branches and shorter chains after sonoenzymolysis reactions.