Effect of degradation methods on the structural properties of citrus pectin

- The molecular mass and structure of degraded pectin with different methods were investigated.
- The pectin degraded by acid, ultrasound-assisted acid and ultrasound with different time had equivalent molecular mass.
- The main chain of degraded citrus pectins with different methods could be preserved.
- Acid degraded pectin was completely free of neutral sugar-side chains.
- The morphology of original pectin was different from that of degraded pectins by AFM analysis.

The molecular mass and its distribution of citrus pectin degraded by different methods were investigated. The primary structure and nanostructure of the degraded products were also identified. The results indicated that acid (80 °C, 12 h), ultrasound-assisted acid (25 °C, 2.5 h) and ultrasound (25 °C, 1.5 h) degraded pectins had equivalent molecular mass. The molecular mass distribution of ultrasound-assisted acid and ultrasound degraded pectins were less polydisperse than that of acid degraded pectin. According to HPLC, IR and NMR analysis, the main chain of ultrasound degraded pectin could be preserved. By contrast, acid degraded pectin was completely free of neutral sugar-side chains. Furthermore, the esterification level of ultrasound-assisted acid and ultrasound degraded pectins was considerably lower than that of original pectin, whereas that of the acid degraded pectin was nearly equal to zero. AFM analysis indicated that the morphology of original pectin was different from that of degraded pectins. The length of linear chains of degraded pectins was shorter and density of branches was lower, compared with that of original pectin. The results indicated that the ultrasound degradation method has the advantage of being timesaving, milder and environment-friendly.