Effects of substitution level and particle size of extruded soybean hull fractions on physicochemical and sensorial properties of high-fiber pan bread during storage.

The effect of adding different fractions of extruded and non-extruded soybean hull to wheat flour at 20% and 30% and two-particle size levels (smaller and larger than 150 µm) was studied on the physicochemical, sensorial properties, and the shelf-life of high-fiber molded bread. Increasing the amount of all different fractions of the soybean hull raised the water absorption of the dough. It also increased the ash and crude fiber contents, bread crust lightness, redness and yellowness, bread crumb hardness as well as the cells number per unit area of the crumb. Moreover, it reduced the moisture content, specific volume, porosity, and overall acceptability of the pan bread. The treatments containing the fractions with larger particle sizes of the soybean hull had higher dough stability time, bread-specific volume, porosity, and lightness, as well as lower crumb hardness and moisture content, and crust redness and yellowness than the corresponding ones with finer particle sizes. The samples prepared with the extruded fractions with smaller particle sizes showed lower moisture content, hardness, porosity, and specific volume. After studying the bread staling, moisture content and overall acceptance of the samples decreased. In addition, the enthalpy in differential scanning calorimetry (DSC) and the signal intensity in x-ray diffraction (XRD) increased during storage. In many cases, the bread with the large-sized extruded fractions of soybean hull at the substitution level of 20% was the most suitable product in most of the variables studied.

Optimization of the extrusion process through response surface methodology for improvement in functional and nutritional properties of soybean hull.

Soybean hull as a rich and inexpensive source of dietary fiber and because of its health properties, is a good option for supplying dietary fiber to various food industries. Optimization of the extrusion process and the effects of its variables [Feed moisture (35-45%), screw speed (160-200 rpm), and temperature (75-95 °C)] were investigated on the structural, nutritional, and functional properties of soybean hull by response surface methodology. Based on response surface analysis, the maximum soluble dietary fiber content and water absorption index in addition to the minimum specific mechanical energy and anti-nutritional composition of tannin were obtained at a feed moisture content of 42.58%, screw speed of 182.46 rpm, and temperature of 87.43 °C. The extrusion process also increased the rate of swelling capacity, solubility index, yellowness, and redness of the samples. It also reduced the oil absorption index and lightness in comparison with the control. The FTIR spectroscopy did not show a new functional group and the urease test (trypsin inhibitor activity) was negative in the extruded samples.