Glucuronoarabinoxylans from maize kernel cell walls are more complex than those from sorghum kernel cell walls

Abstract

Water-unextractable solids (WUS) were isolated from maize kernels. They contained 7% of protein, 8% of starch and 57% of non-starch polysaccharides (NSP). These NSP were composed mainly of glucose, xylose, arabinose, and glucuronic acid. Sequential extractions with a saturated Ba(OH)2-solution (BE1 extract), and distilled water (BE2 extract) were used to solubilize glucuronoarabinoxylans from maize WUS. Cellulose remained in the insoluble residue. The glycosidic linkage composition of the extracts and their resistance to endo-xylanase treatment indicated that the extracted glucuronoarabinoxylans were highly substituted. In the maize BE1 extract 25% of the xylose was unsubstituted, 38% was monosubstituted and 15% was disubstituted. A new measure for the degree of substitution is defined. The resulting degree of substitution for maize BE1 arabinoxylan (87%) is higher than for sorghum BE1 arabinoxylan (70%). The glucuronoarabinoxylans in maize BE1 can be degraded by a sub-fraction of Ultraflo, a commercial enzyme preparation from Humicola insolens. The digest contains a number of series of oligomers: pentosen, pentosenGlcA, pentosenhexose, and pentosenGlcA2.