Characterization of cell wall polysaccharides from Sicana odorifera fruit and structural analysis of a galactan-rich fraction pectins as side chains

Sicana odorifera is a Brazilian native fruit. In this work, cell wall polysaccharides from S. odorifera pulp were isolated by sequential extraction with water, citric acid, and sodium hydroxide solutions. The monosaccharide composition of crude polysaccharide fractions was determined. The aqueous fractions displayed the highest yields and they were constituted by pectins, having mainly galactans as side chains. The citric acid fraction (SCA) had galactose as the main component. The hemicellulosic fractions consisted mainly of xylose, mannose, galactose, and glucose, suggesting the presence of xyloglucans, xylans and mannans. The SCA fraction was further purified, resulting in a linear galactan (SCAI2). NMR and methylation analysis showed that SCAI2 was a β-(1→4) d-galactan with molar mass of 17,560 g/mol, determined by light scattering. The presence of a linear galactan in free form in fruits is unusual because these polymers usually occur as side chains of type I rhamnogalacturonans.