Analysis of wheat arabinoxylans from a large-scale isolation

Abstract

Dietary fibre is of interest because of its nutritional activity and its role in the aetiology of some diseases. Arabinoxylans form the major part of wheat dietary fibre and this paper describes the large-scale aqueous and alkaline (0·2 M NaOH) extractions of a wheat milling by-product which yielded approximately 450 g and 1200 g of arabinoxylan-rich materials, respectively. The structures of the arabinoxylans were investigated using acid hydrolysis, methylation analysis and 1- and 2D-NMR experiments. The polysaccharide is confirmed to be a β-(l-4)-xylan substituted with a-L-arabinose (arabinose:xylose ratio of approximately 0"60) substituted at 02 and 03. Methylation analysis and ¹H-NMR data indicated that the arabinoxylans from the aqueous extraction were very similar in structure to those isolated by alkaline extraction. Both were similar to arabinoxylans isolated directly from wheat by similar laboratory scale procedures. Detailed ¹H-¹H-NMR homonuclear and ¹H-¹³C-NMR heteronuclear correlation spectroscopy analysis of a partially depolymerized sample confirmed the structure of the arabinoxylans and allowed an almost complete assignment of resonances in both the ¹H- and ¹³C-NMR spectra. It was concluded that the nutritional activities ascribed to these materials are also likely to occur when they are ingested as components of complete foods.