WATER UNEXTRACTABLE POLYSACCHARIDES FROM 3 MILLING FRACTIONS OF RYE GRAIN

Water unextractable material from bran, an intermediate milling fracti on and sieved flour of rye grain were sequentially extracted at room t emperature with saturated barium hydroxide, water, 4 M potassium hydro xide and water followed by extraction with 2 M potassium hydroxide in a boiling water bath, giving repeatable recoveries of extracts and pol ysaccharide residue compositions in collected fractions. Total recover ies of polysaccharide residues in extracts and residue from the differ ent water unextractable materials were 78-88%. Extracts in which 90-93 % of the carbohydrates were arabinose and xylose residues were obtaine d by extraction with saturated barium hydroxide. Subsequent extraction with water yielded a fraction in which 64-68% of the carbohydrates we re glucose residues. The extraction with hot alkali resulted in extrac ts in which 85-89% of the carbohydrates were arabinose and xylose resi dues. The ara/xyl ratio in the collected fractions ranged from 0.1-1.3 , with the lowest ratios in fractions that precipitated after neutrali sation of the 4 M potassium hydroxide extract and the highest ratios i n the unextractable residues. Structural characterisation with H-1-NMR spectroscopy revealed varying substitution patterns for arabinoxylans in the different extracts and that glucose residues in the extracts e ssentially originated from mixed-linked beta-glucan. The proportion of disubstituted xylose residues was lower in barium hydroxide extracts compared to the other main extracts. A highly branched heteroxylan was extracted with hot alkali. The polysaccharides found in the correspon ding extracts for all the starting materials had generally similar str uctural features, but the yield differed considerably. Copyright (C) 1 996 Elsevier Science Ltd