Structural characteristics and gelling properties of citrus pectins after chemical and enzymatic modifications: Conformation plays a vital role in Ca-induced gelation.

Due to the excellent health benefits of rhamnogalacturonan I (RG-I)-enriched pectin, there has been increasing research interest in its gelling properties. To elucidate its structure-gelation relationship, chemical modifications were used to obtain RG-I-enriched pectin (P11). Then, enzymatic modification was performed to obtain debranched pectins GP11 and AP11, respectively. The effects of RG-I side chains on structural characteristics (especially spatial conformation) and gelling properties were investigated. Among the low-methoxylated pectins (LMPs), AP11, with a loose conformation (Dmax 52 nm) showed the poorest gelling, followed by GP11. In addition to primary structure, spatial conformation (Dmax and Rg) also showed strong correlations (r > 0.8) with gelation. We speculate that compact conformation may shorten distance between pectin chains and reduces steric hindrance, contributing to formation of strong gel network. This is particularly important in LMPs with abundant side chains. The results provide novel insights into relationship between spatial conformation and gelling properties of RG-I-enriched pectin.