It is well known that storage modulus (G′) represents solid-like behaviour, whereas loss modulus (G″) symbolises liquid-like behaviour. The damping factor (tan δ) is the ratio of G″ to G′. An amplitude sweep test was performed to detect the structural stability, strength, and dynamic yield point in the dough and to determine the Linear Viscoelastic Region (LVE) of the dough. The yield point is where G′ and G″ crossover and generally, a higher G′ and a lower tan δ suggest a more elastic and solid-like behaviour. At a strain of 4.61% which was a crossover point of G′ and G″ of WWF dough, tan δ of WWF, WWF plus 10% of SBH-T, and WWF plus 10% of SBH-C doughs were 1.06 ± 0.1, 1.13 ± 0.08, and 1.43 ± 0.12, respectively, suggesting that, under same strain, WWF plus SBH-T dough showed more liquid-like behaviour, followed by WWF plus SBH-C dough, and lastly WWF dough. This increase in liquid-like behaviour with DF content enhanced expansion of WWF dough during processing. The effect of fibre on dough viscoelastic properties, then, appears to increase dough elasticity to affect the water–flour ratio.
The influence of inulin addition on the rheological properties of common wheat dough and bread quality were evaluated using farinograph and dynamic rheological measurements, the results showed that G′ gradually increased and tan δ decreased with increasing levels of inulin HP and HP-gel, which contribute to the overall dough elasticity and strength ( Peressini & Sensidoni, 2009). In our study, it was observed that the 10% addition of SBH-T into WWF slightly affected the dough viscoelastic behaviour, which may be desirable in dough performance.
4. Conclusions
There is an increasing interest in maximising the utility of waste streams from processed fruit and vegetable in order to boost economic efficiency and reduce waste. In this study, the yellow soybean hulls, one of many possible waste streams, was processed by mimicking different environments of the human digestive system, such as the acidic environment of the stomach and basic environment of the human small intestine, to purify dietary fibre by digesting/removing starch, protein, fat, and pigments. This study may allow an improved utilisation of this resource, which is currently underexploited.
Because the way of processing this agricultural byproduct determines the physicochemical properties and functionality of fibres, differences among the TDF, IDF, and SDF, as well as the potential applications, are considered in this study. The results indicated that colour of lightness was significantly improved. There was also an approximately 50% increase in TDF in the treatment compared to the control. Significant differences were observed in physicochemical and functional properties between treatment and control, with the treatment exhibiting significantly lower WAI and WSI. The mean particle size in SBH-C and SBH-T were 225.6 ± 1.1, 182.7 ± 0.7 μm, respectively. Additionally, the whole wheat flour with 10% SBH-T showed more liquid-like behaviour, which affected the dough viscoelastic property slightly, suggesting possible use in the development of fibre enriched foods. To the best of our knowledge, this is the first study to develop dietary fibre from yellow soybean hulls. It is also the first rheological evaluation of the application of soybean hull fibres in dough. Fibers from yellow soybean hulls could have great potential in various food applications due to their functional properties. Further investigations are needed to establish the precise functions of fibre components on human health and nutrition.