ISOLATION, SEPARATION AND CHARACTERIZATION OF WATER-SOLUBLE NONSTARCH POLYSACCHARIDES FROM WHEAT AND RYE

The water holding capacity of the dough and the freshness of the bread made of rye and wheat are much dependent upon their content of non-starch polysaccharides (NSP), most of which are polymers of xylose and arabinose, i.e. pentosans. The yield of water soluble pentosans from rye flour (1.76%) was higher than that of wheat flour (0.59%), and the xylose to arabinose ratio of rye pentosans was 1:36 while it was 1:16 for wheat pentosans. The galactose content in wheat pentosans was 17% of the total monosaccharides. In rye pentosans the content of galactose was lower (3.5% of the total monosaccharides). The total content of monosaccharides in wheat pentosans (65%) was slightly lower than that in the rye pentosans (71.7%). The weight average molecular weight of rye pentosans (770 000) was higher than that of the wheat pentosans (255 000). The number average molecular weight of the pentosans from rye was 90 000 while the corresponding figure for wheat was 61 000. The rye pentosans showed a higher degree of polydispersity in solution than the wheat pentosans. The separation of the pentosans on a DEAE-Sephadex column resulted in five fractions. The first two fractions contained mainly arabinose and xylose and the protein content in these fractions was approximately 1%. The protein content of the fractions increased with the increased concentration of the borate. The Xyl:Ara ratio was 2:23 and 2:39 in fractions I and II of wheat and 1:63 and 2:32 in fractions I and II of rye. Galactose appeared in fractions IV and V in wheat and fractions IV, V-A and V-B in rye along with some arabinose which suggests the presence of arabinogalactans in these fractions.