Unraveling the effect of dietary fibre on biopolymer structures and interactions in (frozen) dough products
Dietary fibre (DF) is a vital ingredient in our diet that has nutritional benefits regarding alleviation of the risk on non-communicable diseases. DF fractions can affect the dough rheology and bread quality negatively but DF may be used to reduce the negative effects of freezing on dough and bread quality. Therefore, this research was designed to evaluate the effect of inclusion of different soluble DF on water mobility, protein structures and interactions, dough rheology and bread quality of fresh and frozen dough products. Soluble DF extracted (enzyme-assisted aqueous extraction methods) were used in 4.0 and 8.0% (w/w) flour substitution levels to produce fibre-enriched bread loaves. Substitution with DF increased the percent water absorption as expected, in line with the high-water absorption capacity associated with DF. DF extracted from wheat bran (WDF) and quinoa (QDF) substitution increased the bread volume but these DF also increased the pore sizes in the crumb. A loaf volume increase was observed for the 4.0% substitution level with barley DF (BDF). Soluble flax gum (SFG) substitution caused an increase in the bread loaf volume and yielded an acceptable crumb texture and structure. BDF and SFG substitution both affected dough water mobility, freezable water content, dough rheology and gas retention ability. SFG did not result in a reduction in water mobility but an increase. SFG at 8.0% caused a reduction in G′ and G” in dough displaying a lower resistance to deformation with higher extensibility. SFG at 8.0% yielded larger bread loaf volumes after 8 weeks of frozen storage of dough. Bread crumb hardness values and the starch retrogradation rate in SFG breads were lower than BDF and control. Higher bulk viscosity observed for SFG dough liquor may have a positive effect on the stabilization of gas cells in the dough which improves the bread crumb structure. Findings of this research indicate that both BDF and SFG can be used to partially substitute wheat flour without compromise the bread quality. Among two DFs SFG showed a promising effect in reducing damage caused to dough structure during frozen storage and in reducing the staling rate of bread.