A novel (1 → 4)-α-d-glucan isolated from the fruits of Opuntia ficus indica (L.) Miller

A water-soluble polysaccharide (PS-1) was isolated from the fruits of Opuntia ficus indica (L.) Miller by hot water extraction, anion-exchange and gel-permeation chromatography (yield 167.5 mg/kg raw fruit; [α]D161 + 192° (c 1.0, H2O); total neutral sugar content 96.60% w/w; weight–average molecular weight (Mw) ∼360 kDa). Structural characterisation was performed by monosaccharide analysis and linkage analysis (methylation analysis, periodate oxidation and Smith degradation) on full and partial acid hydrolysates, followed by alditol acetylation, and product quantification by GC/GC–MS. Spectroscopic analysis (FT-IR and 1H/13C NMR) was also performed. Polysaccharide PS-1 was found to be an α-d-glucan with a (1 → 4)-linked α-d-Glcp backbone, with (1 → 6)-linked (1 → 4)-α-d-Glcp side chains, side chains being short in length with no additional branching, and a minimum branching of ∼1 in every 9–11 backbone units. The distribution of side chains lengths and corresponding branching density requires further investigation.