Study on low methoxyl pectin (LMP) with varied molecular structures cross-linked with calcium inducing differences in the gel properties

The gel properties of pectin are significantly connected with its molecular structure. In this paper, we investigated the relationship between low methoxyl pectin (LMP) molecular structure and gel strength in the same degree of esterification (DE) range. LMP with DE of 31% ± 2% was prepared from citrus peels by acid, alkaline, enzymatic, and citric acid/sodium citrate solution methods. And based on data from monosaccharide composition, Mw, and NMR spectroscopy, the proportion of structural regions was speculated. The result revealed that C-LMP (pectin de-esterified by citric acid/sodium citrate solution method) was a highly branched macromolecular polysaccharide with short HG and enriched RG-I, with HG and RG-I proportions of 19.37% and 76.96%. According to the gel property investigation, of all the LMP samples, A-LMP-0.7 (pectin de-esterified by acid method at pH 0.7), which possessed lengthy HG and enriched RG-I domain, exhibited the best gel strength. C-LMP, A-LMP-0.5 (pectin de-esterified by acid method at pH 0.5), and B-LMP (pectin de-esterified by alkaline) failed to form a complete gel due to the low HG linearity, sparse RG-I and low Mw, respectively.