Study On The Effect Of Oat Or Buckwheat Flour On Properties Of Mixed Dough And Quality Of Chinese Steamed Bread

Oat and buckwheat are larger output and higher nutrition coarse cereals in our country. The influence factors of higher replacement level of oat or buckwheat flour on dough properties and quality of Chinese steamed bread(CSB) were mainly studied in this thesis in order to provide theoretical guidance for improving the quality of higher content of oat or buckwheat CSB. It’s very important for grains staple food industrialization and improving the human diet. The main research contents and results were as follows:The wheat flour was substituted by oat or buckwheat flour at different levels(0%, 10%, 20%, 30%, 40% and 50%) and the rheological properties of mixed dough and quality of CSB were analyzed. The results showed that with the increase of replacement ratio, the content of wet gluten in mixed flour significantly decreased. Farinographic properties of oat-wheat mixed flour and buckwheat-wheat mixed flour showed different change trends but the extension resistance, extensibility, stretching ratio and the area under the extensographic curve all decreased with the increase of oat or buckwheat flour substitution. Meanwhile, the final viscosity, retrogradation value and the viscoelastic moduli(G’ and G’’) all increased, while the pasting breakdown values increased firstly and then decreased. The gas holding properties of mixed dough decreased, the startup time of air leakage shortened and the p H of mixed dough were higher than that of wheat dough. And with the replacement level increased, the specific volume and springiness of CSB decreased and its hardness increased. In brief, the higher oat or buckwheat flour replacement rate(more than 30%) was unable to produce high quality CSB.Based on the 50% substitution ratio, the yeast gas productivity, wheat gluten, bran and starch, which influenced dough properties and CSB quality with higher oat or buckwheat flour substitution rate, were researched. The results were as follows.Higher oat or buckwheat flour replacement rate would decrease the gas production of yeast during dough fermentation. Moreover, compared with the gas-producing rate of yeast in wheat dough, the gas-producing rates in oat-wheat and buckwheat-wheat dough were lower at early stage of fermentation(before 90 minutes), while higher at later stage of fermentation(after 90 minutes), which indicated the addition of oat or buckwheat flour would affect the fermentation activity of yeast in mixed dough.The addition of gluten could significantly improve the rheological properties of mixed dough, increase the dough stability, while decrease softening degree. The extension resistance, extensibility and the area under the extensographic curve all increased as gluten added. The gas holding properties of mixed dough were also improved. The specific volume and springiness of CSB all increased and the hardness of CSB decreased and the pore distribution of crumb were improved, indicating that the dilution of gluten protein by higher substitution levels of oat or buckwheat flour was an important factor in deterioration of dough properties and CSB quality. The improving mechanisms of wheat gluten on mixed dough properties and CSB quality were the content of wet gluten and disulfide bonds of mixed dough significantly increased by wheat gluten addition, hydrophobic force significantly enhanced(p ? 0.05), while ionic bonds gradually weakened. And hydrogen bonds in oat-wheat dough gradually weakened but in buckwheat-wheat dough gradually enhanced. These chemical interactions were close to those in wheat dough by appropriate extra gluten addition, which improved the conformation and microstructure of gluten protein in mixed dough. The properties of mixed dough and quality of CSB were improved to a certain extent.Removing bran made the pasting parameters of oat flour all decreased except pasting temperature increased and made the final viscosity and retrogradation value of buckwheat flour increased, while the breakdown values and pasting temperature decreased. The gas production declined, while the holding gas properties of mixed dough were slightly improved by removing bran. Oat flour without bran greatly delayed the time of dough air starting leakage and made the mixed dough pH apparently decreased. But removing bran had little effect on pH of buckwheat-wheat dough. Shortly, removing bran was good for oat steamed bread but had negative impact on buckwheat steamed bread.The effect of oat β-glucan on quality of CSB and β-glucanase on quality of oat-wheat CSB were studied. The results revealed that more than 0.50% β-glucan content would decrease wheat CSB specific volume and elasticity, while increase its hardness, and darken the color of CSB, indicating that the higher content of β-glucan in oat flour was another important factor to deteriorate the quality of oat-wheat CSB. Adding 0.15% β-glucanase could significantly improve the oat-wheat CSB quality, obtaining higher specific volume, springiness and lower hardness of CSB, while adding β-glucanase has little effect on the color of CSB.The properties of wheat, oat and buckwheat starch and its simulative dough were further investigated. These three kinds of starch were all typical A-type crystal structures. But compared with the wheat starch, the water-holding and swelling capacities of oat starch were higher and the solubility was lower. While the water-holding, solubility and swelling capacities of buckwheat starch were all lower than those of wheat starch. Scanning electron microscopy also showed that their starch granules form were different, which oat and buckwheat starch particles were significantly smaller than wheat starch and furthermore, wheat starch was ellipsoidal with smooth surface, oat starch was uneven and had compound grain structure and buckwheat starch was polyhedral shape with smooth edges and corners and there were evacuation pores in its particle surface. These different characteristics among grain starch made the simulative dough exhibit different properties. The gluten network of simulative dough was damaged by oat and buckwheat starch, suggesting that the starch was also one of the important factors to affect the mixed dough properties.