Complex influence of structural characteristics of low-methoxyl pectins on rheological properties of semi-solid Ca-gels.

The semi-solid Ca-gels were prepared from low-methoxyl pectins (methoxylation degree DM 4-36 %) of Oberna behen, Potamogeton natans, Tanacetum vulgare, Comarum palustre, Bergenia crassifolia, and Heracleum sosnowskyi. Pectins are characterized by Mw of 77-556 kDa and different content of HG and RG-I. The gels were prepared by addition of Ca ions at varying stoichiometric ratios, R = 2 × [Ca]/[COO], of 0.2-0.6, and a fixed pectin concentration of 10 g/L. It was shown that the presence of certain sets of structural characteristics in low-methoxyl pectins from different sources leads to the formation of gels with similar rheological properties. Pectins with Mw 77-98 kDa, DM 6-14 % form stiffer Ca-gels than pectins with Mw 218-253 kDa, DM 24-36 % at the same R. Pectins with Mw 346-556 kDa form the strongest Ca-gels. Their high Mw compensates for the influence of DM on the properties of Ca-gels. The stability of gels in PBS (pH 7.4) is determined mainly by proportion of 1,4-linked non-methoxylated GalA in pectins. Pectins with DM 4-14 % form more stable Ca-gels in PBS than pectins with DM 21-36 %.