WATER-UNEXTRACTABLE CELL-WALL MATERIAL FROM WHEAT-FLOUR .1. EXTRACTION OF POLYMERS WITH ALKALI

Water-unextractable cell wall material (WUS) prepared from wheat flour was extracted sequentially with saturated Ba(OH)2, 1 M KOH and 4 M NaOH. The resultant extracts, which together contained 96% of the total WUS in the flour, were enriched in arabinoxylans, (1 → 3,1 → 4)-β-glucans and glucomannans, respectively. The remaining 4% of the wheat flour WUS was mainly cellulose. Methylation analysis of the arabinoxylans showed that the xylopyranosyl residues were substituted at 0-3 or 0-2,3 with mainly terminal arabinofuranosyl residues. Only minor amounts of 0-2 substituted xylose were found. The degree of substitution of xylopyranosyl residues was highest in the NaOH extract and lowest in the first Ba(OH)2 extract, with that in the second Ba(OH)2 extract and in the KOH extract being intermediate. Only minor differences in protein content and amino acid composition were observed among the extracts. Alkali-extractable arabinoxylans had slightly higher apparent molecular weights than water-extractable arabinoxylans. The alkali-extractable (1 → 3,1 → 4)-β-glucans and (gluco)mannans had substantially lower apparent molecular weights than the arabinoxylans. © 1992, Academic Press Limited. All rights reserved.