Effects of soluble and insoluble fibres on pasting and retrogradation of wheat flour and quality of bread

Abstract

This study aimed to investigate the effect of selected fibres on pasting as well as short-term and long-term retrogradation of starch in wheat flour and to investigate the quality of fibre-added white pan breads. Two soluble fibres, tara gum (TG) and k-carrageenan (CAR), and one insoluble fibre, cellulose (CEL), were added to wheat flour at different levels (1.0, 1.5 and 2.0%). Regarding pasting behaviour, addition of soluble fibres was found to cause an increase in peak, trough, breakdown, and final viscosity. Meanwhile the addition tended to decrease setback viscosity and pasting temperature. In contrast, insoluble fibre addition posed a minimal effect on the pasting properties of wheat flour. Regarding starch gelatinisation, all fibres minimally affected gelatinisation temperature but did reduce the gelatinisation enthalpy (ΔHG). To monitor long-term retrogradation, enthalpy of retrogradation (ΔHR) of the samples stored for 6, 10 and 14 days was observed. It was found that most of the fibre reduced in ΔHR while TG at all concentrations caused an increase. As of gel firmness, fibre addition was shown to increase firmness of the freshly prepared flour gel, with CAR samples exhibited the highest firmness. However, during storage, the fibre-added samples demonstrated a slower increase in gel firmness than the control. At 14 days of storage (4°C), all gel samples, except 1.5% TG and 2.0% TG, possessed significantly lower gel firmness as compared to the control (p≤0.05). Based on the above study, the optimum concentration (1.0% TG, 1.5% CAR and 2.0% CEL) were selected and added in white pan breads to investigate quality of freshly prepared bread (Day 0) and of those stored at room temperature for 6, 10 and 14 days. At the beginning of the storage, moisture content of all breadcrumbs was similar in value. However, during prolonged storage (≥10 days), both soluble and insoluble fibres were found to help retain moisture. As to specific loaf volume, CEL bread interestingly displayed the highest value while CAR resulted in a bread with the lowest specific loaf volume. In terms of textural property, both soluble and insoluble fibres significantly demonstrated lower hardness than the control. The decrease in hardness, gumminess and chewiness and an increase in springiness and cohesiveness signified that the fibres play a role in maintaining quality of the breads. All fibre-added breads had smaller and evenly distributed air cells when compared to the control. All the breadcrumbs were yellow in colour, with orange-yellow bread crust. Both crumb and crust colour demonstrated minimal changes during storage. In summary, both soluble and insoluble fibres proved to have a positive effect on quality of the freshly baked as well as the stored breads.