Molecular weight distribution and content of water-extractable β-glucan in rye crisp bread

Rye crisp doughs and breads were made from three rye flours with different falling numbers (i.e. different enzyme activity), with or without oat bran rich in β-glucan (OBG) added, and with different fermentation times. The aim of the study was to investigate the effect of endogenous enzymes in the flour on molecular weight and content of water-extractable β-glucan in the doughs and breads. The molecular weight distribution of β-glucan was unimodal for the flours, with a calcofluor average molecular weight of about 90×10⁴ g/mol for the rye flours, and 150×10⁴ g/mol for rye flours with added OBG. The molecular weight decreased with increasing fermentation time for all doughs, but was almost unchanged during oven-baking. The calcofluor average molecular weight was highest in doughs and breads made of flour with highest falling number (i.e. lowest enzyme activity), indicating that the endogenous enzymes in the flour were responsible for the breakdown of β-glucan. During fermentation, water-extractable β-glucan was released from the insoluble matrix, probably by the endogenous enzymes in the flour. When the molecular weight of the water-extractable β-glucan decreased, they probably associated with each other or with other components in the dough to form unextractable complexes. The content of water-extractable β-glucan did not change during oven-baking.