The selective extraction of glucuronoarabinoxylans from sorghum endosperm cell walls using barium and potassium hydroxide solutions
Verbruggen, M.A. | Beldman, G. | Voragen, A.G.J.
Various populations of hemicellulosic material were solubilised from water-unextractable cell wall material (WUS) of sorghum (Sorghum vulgare cv. Fara Fara) by sequential extractions with alkali. Saturated Ba(OH)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 glucuronoarabinoxylans (GAX) from sorghum WUS. Cellulose remained in the residue. In total over 90% of all GAX originally present in the WUS were recovered, 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 the extractants tested for GAX. (1 leads 3), (1 leads to 4)-beta-D-glucans were found predominancy in the fraction obtained by washing with water after the extraction with saturated Ba(OH)2. All extracted arabinoxylans were highly substituted (arabinose/xylose> 1) and contained, besides L-arabinose and D-xylose, the acidic sugars D-glucuronic, 4-O-methyl-D-glucuronic 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 presence of a bivalent cation.
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