Structural analyses of apricot pectin polysaccharides

Abstract

Apricot pectin polysaccharides' fine structure was performed using HPSEC, HPAEC-PAD, GC-MS, NMR and FTIR spectroscopies. Purified pectin fraction (F1AP) was composed of D-galacturonic acid, L-rhamnose, D-arabinose and D-galactose, Mw ∼ 1588 kDa. F1AP was eluted by water and with 0.2 M NaCl from DEAE Sepharose fraction resulting in two distinct fractions, F1AP1 and F1AP6, with different structures, molecular weights, and conformations, providing insights into their structural diversity. F1AP1 neutral properties were related to its association with protein. F1AP1 had a backbone of (1 → 4)-linked-D-galacturonic acid and (1 → 2)-linked-L-rhamnopyranosyl residues branched with arabinogalactan including multiple glycosidic linkages of T-α-Araf, 3-α-Araf, 5-α-Araf, T-α-Arap, 2-α-Arap, t-Galp, 2-Galp, 3-Galp, 4-Galp, 6-Galp, 2,4-Galp, 3,4-Galp, 3,6-Galp and 4,6-Galp side chains, having methyl and acetylated groups, and a high molecular weight (1945 kDa). The Mark-Houwink exponent was 0.276, indicating a compact spherical conformation. While the other F1AP6 fraction consists predominately of less methylated HG regions of pectin polysaccharides. The molar mass of this fraction was 117.5 kDa, which adopted a stiffer and random coil conformation. This knowledge allows us to evaluate how the balance of chemical structure and physical properties of the two pectin domains may manifest itself in the isolated structure of apricot pectin and its applications.

Keywords: Apricot; Apricot pectin; Arabinogalactan; HG; Molecular weight; NMR spectroscopy; RG-I.