The Carbohydrates of the Gramineae. XI. The Constitution of the Water-Soluble Polysaccharides Derived from Bread Crumb./p> K. A. Gilles, W. F. Geddes, and F. Smith. Copyright 1961 by the American Association of Cereal Chemists, Inc. /p> The so-called "soluble starch" of bread consists of starch and a pentosan. "Soluble starch" from fresh bread represented, on a dry weight basis, 4.3% of the crumb and contained 11.7% pentosans; whereas, in stale bread from the same lot, the "soluble starch" represented 3.3% of the crumb and contained 19.3% pentosans. Water-soluble pentosans present in the "soluble starch" inhibited the retrogradation of amylose. Acetylation of the "soluble starch" fraction followed by fractional precipitation of the resulting acetate yielded a fraction, [alpha]D27-44.5 degrees in pyridine, which upon deacetylation and hydrolysis gave a polysaccharide complex containing xylose, arabinose, and glucose in the mole ratio five to four to three (5:4:3) respectively. This pentosan-rich fraction consumed 0.87 mole of periodate per pentose residue with the formation of formic acid corresponding to an average "repeating unit" of about 9. The pentosan fraction was methylated via the acetate and fractionally precipitated. Hydrolysis and quantitative analysis of the resulting glycosides by the phenol-sulfuric acid procedure showed D-xylose (1 mol.), 2-O-methyl-D-xylose (1 mol.), 2,3-di-O-methyl-D-xylose (2.7 mol.), and 2,3,5-tri-O-methyl-L-arabinose (1.7 mol.). These methylation results show that the pentosan in the water-soluble polysaccharides of bread crumb possesses a highly branched structure and that it is structurally similar to the pentosan in the original flour. | |
