Effect Of Barley Flour On Dough Properties And Bread Quality And Its Improver Study

Barley with special flavour is rich in nutrition. China is rich in barley resources which are in low price but best in quality. But compared with wheat flour, barley flour is able to form hard plastic dough rather than a iscoelastic dough. Especially when the supplementation of wheat flour with barley flour is more than30%, it will cause a significant decrease in quality of fermented flour products like bread. As a result, the use of barley in food, especially in fermented flour products, is limited. Therefore, the development of barley products is badly affected. And the key to solving the problem is to reveal the fundamental reason that how the fermented flour products quality is as affected by barley in order to find a suitable improver and study the improved mechanism.In this paper, two main influence factors gluten and β-glucan were elected to reveal the fundamental reason for bread quality deterioration affected by barley flour. Meanwhile, by combing the effects of β-glucan and β-glucanase, barley-wheat composite dough and bread quality affected by β-glucan were analyzed and the β-glucanase improved mechanism was investigated. The main study contents and results are as follows:1.10%-60%of wheat flour was substituted with whole barley flour (hereinafter referred to as barley flour), and the effect of barley flour on dough properties and bread quality were investigated. The results showed that, with increasing addition of barley flour, the barley-wheat composite flour color became darker and water absorption increased. Dough development time, stability time and C2(weakening value), as well as the dough extensibility and maximum resistance decreased. Meanwhile, microstructures of dough added with barley flour changed and coarser structures presented. In the range of20%-60%, the gas cells broke, and cell structures hardly be found. For bread quality, when the addition level of barley flour, the specific volume, springiness and sensory quality decreased, hardness of bread increased. Meanwhile, the area of cells decreased, holes increased, and slice brightness decreased. Although the bread quality decreased with10%-20%addition of barley flour, the overall sensory quality of bread could be accepted. However, the bread baking quality decreased significantly with excess barley flour (30%-60%), and grainy texture like sponge of bread disappeared.2. Focusing on the gluten protein and β-glucan, the main factors that influenced bread quality by barley flour and the effects on bread quality were investigated The results showed that, compared with wheat flour, barley flour was not lack of total protein and two structural protein (glutenin and gliadin) which can form gluten and sulfur-containing amino acid. However, with increasing addition of barley flour, the content of wet gluten decreased significantly. The main reasons were the ratio of glutenin and gliadin was not conducive to the formation of gluten and containing no HMW-GS in barley flour. Added certain wheat gluten could improve the farinograph properties of barley-wheat composite flour and relieve the shortage of barley flour lacking of gluten. The content of β-glucan in barley flour (5.4%) was much more than wheat flour (0.18%). The results showed that, when β-gulcan added into wheat flour more than0.5%, wheat dough resistance to extension increased, while, tensile length, development time, stability time and C2of wheat dough decreased significantly; when β-gulcan added into wheat flour more than1.5%, the specific volume and springiness decreased, while hardness increased. These results indicated that dough appeared very obvious degradation affected by P-glucan. Therefore the main factors that barley flour caused deterioration in the bread quality were gluten and β-glucan.3. The influence of different levels (0.02%,0.04%,0.06%and0.08%, based on composite flour) of P-glucanase on the properties of dough and bread from barley (30%)-wheat (70%) composite flour were studied. These results indicated that, the viscosity of with composite flour decreased with increasing addition of β-glucanase; although dough development time, dough stability and protein weakening value decreased obviously, dough properties such as softness and elasticity as well as microstructure was improved. β-glucanase also significantly improved the volume and texture of composite bread, bringing it a better taste, flexibility and overall sensory quality of baking. Meanwhile, β-glucanase chould help to improve the anti-aging properties of bread, thus extending the shelf life of products. The use of an optimal enzyme concentration (0.04%) increased specific volume (57.5%), springiness (21%), and reduced crumb firmness (74%).4. On the base of bread qualities affected by β-glucan and β-glucanase, the degradation effect of β-glucan as well as the improvement mechanism of β-glucanase on barley-wheat composite dough and bread quality was studied. These results indicated that the weakening effect of β-glucan was closely related to its molecular weight. B-glucanase decreased β-glucan molecular weight significantly; the results of FT-IR, Raman, SEM and NMR showed that high molecular weight β-glucan with water formed high viscosity gel. On the one hand, the high viscosity gel attached to the surface of gluten network structure, which affected secondary structure of gluten, on the other hand, it competed water with gluten; Therefore, functional performances of gluten were decreased. However,β-glucanase could eliminate the negative effect of the viscous gel. Therefor, it improved the gluten network structure indirectly, and increased the elasticity of wheat gluten.The improvement effects of β-glucanase on barley-wheat composite bread qualities are as follows:(1) the high holding water and high viscosity performances of P-glucan decreased by degrading high molecular weight of β-glucan to low molecular weight oligosaccharide fragments. This effect could promote crosslinking between the gluten protein molecules, thereby alleviating the negative impact of the β-glucan;(2) water in dough were redistributed when water molecules transferred from β-glucan to gluten, which provided the prerequisites for wheat gluten formation and development;(3) β-glucosaccharase, which was produced during yeast activity process, hydrolyzed low molecular weight oligosaccharides to reducing sugar that could be used by yeast. Therefore, carbon source used yeast using increased and the yeast gas ability improved.5. The six parameters were screened by FFD on the basis of bread comprehensive score and the formula of composite improver was optimized, in order to develop barley bread (containing barley flour55%) with both excellent nutrition and quality. The results showed that comprehensive score could be significantly affected by β-glucanase, wheat gluten and a-amylase, and the importance ranking is β-glucanase>wheat gluten>a-amylase; when the transglutaminase, sucrose ester and Vc were added in a certain level, the addition level of the three important factors were optimized by CCD on the base of steepest ascent design result, and the composite improver addition level were β-glucanase0.0649%, wheat gluten7.5269%, a-amylase0.0089%, transglutaminase0.0900%, sucrose ester0.3000%and Vc0.0125%.Improvement effect on barley bread was investigated using C-Cell and texture analyzer. The results showed that the barley bread wrapper length and the number of cells all increased area of holes decreased and specific volume increased by45%compared with the bread without composite improver. Meanwhile, the texture characteristics of fresh and storage period bread were all significantly improved: hardness decreased, springiness increased, and chewiness, as well as appearance quality improved. As a result, the composite improver was suitable for barley food like barley bread with high content barley flour.