THE SELECTIVE EXTRACTION OF GLUCURONOARABINOXYLANS FROM SORGHUM ENDOSPERM CELL-WALLS USING BARIUM AND POTASSIUM HYDROXIDE SOLUTIONS

Various populations of hemicellulosic material were solubilised from w ater-unextractable cell wall material (WUS) of sorghum (Sorghum vulgar e cv. Fara Fara) by sequential extractions with alkali. Saturated Ba(O K)(2)-solutions, followed by distilled water, 1 M KOH, 4 M KOH and 4 M KOH containing 4% (w/v) H3BO3 were used to extract primarily glucuron oarabinoxylans (GAX) from sorghum WUS. Cellulose remained in the resid ue. In total over 90% of all GAX originally present in the WUS were re covered, particularly in the saturated Ba(OH)(2), 1 M KOH and 4 M KOH extracts. Saturated Ba(OH)(2) was found to be the most selective of th e extractants tested for GAX. (1-->3), (1-->4)-beta-D-glucans were fou nd predominantly in the fraction obtained by washing with water after the extraction with saturated Ba(OH)(2). All extracted arabinoxylans w ere highly substituted (arabinose/xylose>1) and contained, besides L-a rabinose and D-xylose, the acidic sugars D-glucuronic, 4-O-methyl-D-gl ucuronic and D-galacturonic acid. The average molecular weight ranged from 210 000-1 300 000, which corresponds with DPs of c. 1500 to 9300. The selectivity of the extractant was apparently enhanced by the pres ence of a bivalent cation.