Structure Characterization and Gelling Properties of Rg-I-Enriched Pectins Extracted from Citrus Peels Using Four Different Methods

Abstract

In recent years, rhamnogalacturonan-I (RG-I)-enriched pectin (RGP) has been recognized as a novel gelling food additive with potentially health benefits. However, the impacts of extraction methods on the chemical structures and gelling properties of RGP remain unclear. This study compared the structural characteristics and gelling properties of RGPs extracted from citrus peel by four distinct methods (low temperature-alkali, high temperature-high pressure, citric acid, and enzyme-assisted extraction). Both the low-temperature alkali and citric acid extractions achieved a satisfactory enrichment effect (54.8 mol% and 51.9 mol%, respectively) by disrupting the HG region; among the methods, while citric acid extraction yielded the highest pectin output (15.5%). Furthermore, selective preservation of neutral sugar side chains was observed in these two methods. The low-temperature alkali method preserved longer side chains with a higher galactose content (18.6 mol%), leading to a compact conformation capable of forming a hard gel by reinforcing the gel structure via strong entanglement. Citric acid extraction resulted in a highly branched RG-I region with increased rhamnose content (5.4 mol%), facilitating more intramolecular hydrophobic interactions and contributing to gel resilience with a higher cross-linked network. These findings offer insights for the further development and production of RGP as a novel, health-promoting gelling agent.

Keywords: Citrus, pectin, RG-I, chemical structure, gelling property