| Okara is the by-product of tofu, soybean milk and other soybean products. With the increase of theconsumption of soy products, a large number of okara were produced every year. Okara is rich in dietaryfiber, protein and other nutrients. Furthermore, okara is abundant and cheap. Therefore, it is a goodresource of dietary fiber. Bread is a popular food in the world. Adding okara can improve the nutritionalvalue of bread. This paper studied the effects of okara’s size and addition on physiochemical property ofwheat bread flour, rheological and textural properties and ultrastructure of dough, the optimal processingtechnology and glycemic index of okara bread.1. The water content of mixed flour decreased with the addition of okara powder, but the ash contentincreased with the addition of okara powder. At the same addition level,the smaller of okara powder size,the lower of ash content was. The whiteness of mixed flour decreased with addition of okara powder, andthe smaller of okara size, the lower of whiteness was. Protein content of okara powder was higher slightlythan wheat bread flour. The peak viscosity, trough viscosity, breakdown, setback, final viscosity, peak timeof mixed flour decreased with the addition of okara powder. The results indicated that adding okara canimprove the thermal stability and anti-aging ability of wheat bread flour.2. The water absorption and development time of mixed flour increased with the addition of okarapowder. At the same addition level, the doughs made from the small size okara powder had higher waterabsorption than the other size okara powder. With the addition of okara powder, the stability time of doughincreased firstly and then decreased, and the weakness of dough reduced significantly. The area under theextensigraph curve, resistance,extensibility, and resistance/extensibility of dough reduced with the increaseof okara powder. The area under the extensigraph curve and resistance of large size okara dough werehigher than the other sizes. The biggest extensibility and resistance/extensibility appeared at10-15%additon for large size okara.3. The hardness of dough increased with the addition of okara powder, and increased fast after20%okara addition. Springiness, cohesiveness, gumminess and chewiness of dough presented a wavy changewith the addition of okara powder, and the biggest values were appeared at10%~15%addition. Okarainceased slightly dough resilience and the biggest value was presented at10%addition. The smaller ofokara powder size, the lower of dough adhesiveness was. The textural properties of dough decreased significantly after fermentation.The results showed that10%~15%addition of okara powder producedoptimal values for most textural properties of dough.4. Scaned electrical micrography showed that with the addition of okara powder the gluten-starchmatrix changed from continuous to discontinuous. The gluten network of dough became poor. Becauselarge particle and irregular shape of large size okara, it can contain some gas during dough mixing. Thedilution and packing effects of large size okara on gluten network were lower than the other okara powders,so the dough quality was better. However, when the addition of okara was higher than15%, the dilutionand packing effects on gluten network were stronger too much. In addition, the doughs made from smalland medium okara powder had denser structure and bigger dilution than doughs made from large okaraflour at the same substitution.5. Three particle sizes okara powder were used to make bread at10%,15%substitution. The resultsshowed that10%addition for large size okara powder was optimal for bread making. The compoundimprovers were optimized by response surface methodology, and the optimal addition were konjac flour0.5%, glucose oxidase0.0007%, calcium stearoyl lactylate0.41%and diacetyl tartaric acid ester ofmonoglycerides0.7%. In vivo and in vitro assessment of the glycemic index (GI) of okara bread was49.09and52.53, respectively, indicating the okara bread belongs to low GI food. |
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