Improvement Of Dietary Fibre Characteristics Of Bran
Aktaş Akyıldız, Eda
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As the use of dietary fibre (DF) in food formulations is challenging and the intake of DF is lower than the recommended levels, the need for high fibre food ingredients, without deteriorative effects on quality, has been increasing during the last few decades. Therefore, in the current study, the effect of steam explosion (SE) and extrusion treatments on microstructure and enzymatic hydrolysis of wheat bran were investigated. The chemical composition of laboratory-scale extracted soluble β-glucan (BG) from oat (16 and 32% BG) and barley fractions (12 and 32% BG), and stability of dispersions prepared from water extracts were also studied. Wheat bran was treated at different steam temperatures and residence times, and then hydrolysed with a commercial enzyme. SE increased the water extractable arabinoxylan (WEAX) and reducing sugar contents of wheat bran. The effect was more pronounced with increased SE temperature and residence time. The highest carbohydrate solubilisation was observed at the severest SE conditions. Enzymatic incubation further increased WEAX content. Supplementation of SE treated bran at 20% replacement level decreased the baking quality of bread. However, enzymatic hydrolysis compensated the negative effect of SE. Phytic acid content of bread supplemented with SE treated bran was lower than the one supplemented with untreated bran. Extrusion treatment was used to modify wheat bran microstructure and DF profile. Fibre solubility increased in all extrusion conditions and the screw speed was found to be the most effective parameter. Physicochemical properties of bran were affected from extrusion treatment. While the water-binding capacities of extruded brans were lower than that of non-extruded wheat bran, their water solubilities were higher. Enzymatic hydrolysis increased the soluble DF content of the bran samples as compared to those of respective samples at the beginning of incubation. Oat and barley fractions were hydrolysed with an enzyme preparation and BG was extracted from hydrolysed samples. Enzymatic hydrolysis resulted in medium and low molecular weight (MW) BG after 2 and 4 h incubation, respectively. MW and concentration of BG affected the stability of dispersions during storage. Barley fractions resulted in higher viscosities than oat fractions. MW of BG in soluble barley fractions was slightly higher than those of oat fractions. Barley extracts contained higher amounts of starch; however, starch did not have a distinct effect on viscosity. The results showed that SE and extrusion treatments can be used to disrupt the wheat bran microstructure and thus to increase the soluble fibre content. Enzymatic hydrolysis can also be used for increasing solubility further. It has also been found that oats BG is a more suitable ingredient for high fibre liquid food systems as compared to barley BG. The outcomes of this study can be utilized for improving the technological functionality of cereal fibres to develop high fibre ingredient for food applications.