Preparation of modified citrus pectin (MCP) using an advanced oxidation process with hydroxyl radicals generated by UV-H2O2

Abstract

An advanced UV-H2O2 oxidation system was developed to prepare modified citrus pectin (MCP) from citrus pectin. A rhamnogalacturonan I (RG-I) enriched MCP fraction with the weight-average molecular weight (Mw) of 44.9 kDa and a MCP recovery rate of 91.2% was obtained under a condition of 30 mM H2O2 and UV irradiation for 5 h. The kinetic study implied that UV-H2O2 oxidation process is more efficient in reducing the Mw than the most commonly used approaches. By comparison of the chemical compositions of MCP and relevant intermediates during continuous UV irradiation, we proposed a functional mechanism of the UV-H2O2 oxidation process. Pectin depolymerization started with an initial random scission, followed by main chain scission through selective oxidative degradation of galacturonic acid linkages, and ended with a chain-end scission. In a minor extent, β-elimination and de-esterification occurred simultaneously throughout the process.