Galactan side chains dominate thermal aggregation of RGI-Rich pectin during drying resulting poor solubility

Rhamnogalacturonan I (RG-I) pectin, abundant in fruit and vegetable waste, exhibits great potential for applications in the food and cosmetics industries. However, RGI-rich pectin tends to aggregate during heat-drying, leading to poor solubility, which severely restricts its utilization. This study delves into the role of RGI side chain structures in aggregation. Different RGI-rich pectins were extracted from citrus and potato and modified enzymatically. The results showed that the solubility of the hydrolyzed pectins (arabinose or galactose side chain shortened to about 50 % of their original length, respectively) was significantly improved, even more than doubled for citrus RGI-rich pectin. Galactose side chain removal showed a more pronounced effect. Meanwhile, the soluble and insoluble fractions were separated, and their structural characteristics were determined. The results showed that the insoluble fraction was found to have a higher length of arabinose and galactose side chains, with greater branching, which contributed to tighter molecular conformations. Additionally, the introduction of urea to disrupt inter-molecular hydrogen bonding significantly enhanced solubility, emphasizing that hydrogen bonds mediate entanglement of RG-I side chains. These findings provide new insights into the thermal aggregation mechanism of RGI-rich pectin, paving the way for strategies to boost its solubility and industrial application performance.