Content and Molecular-Weight Distribution of Dietary Fiber Components in Whole-Grain Rye Flour and Bread

Abstract

Content of dietary fiber and dietary fiber components in whole-grain rye (n = 18) were analyzed. The average total content, when fructan was included, was for dietary fiber 19.9% (range of 18.7−22.2%) and for extractable dietary fiber 7.4% (range of 6.9−7.9%). Arabinoxylan was the main dietary fiber component, with an average total content of 8.6%, followed by fructan (4.1%). During baking of whole-grain rye bread, only small changes in total content of arabinoxylan, arabinogalactan, and β-glucan occurred, while the content of resistant starch increased and the content of fructan decreased in a baking-method-dependent manner. The molecular-weight distribution of extractable arabinoxylan in the flour was analyzed with a new method and ranged from 4 × 10⁴ to 9 × 10⁶ g/mol, with a weight average molecular weight of about 2 × 10⁶ g/mol. During crisp bread making, only a limited degradation of arabinoxylan molecular weight was detected, while a notable degradation was observed in sour-dough bread. The molecular weight of extractable β-glucan in the whole-grain rye flour ranged from 10⁴ to 5 × 10⁶ g/mol, with a weight average molecular weight of 0.97 × 10⁶ g/mol. During bread making, the molecular weight of the β-glucan was substantially degraded.