Mechanism Study On The Effects Of Barley β-glucan On The Properties Of Wheat Dough

In recent years, there is an increasing interest in barley β-glucan(BBG), which has been proven to lower plasma cholesterol, improve lipid metabolism and reduce glycaemic index in humans. As a traditional staple food in China, steamed bread has a tremendous consuming market. Incorporating BBG into wheat flour to prepare steamed bread, can not only enhance its health benefits as a dietary fiber, but also improve the product quality as a hydrocolloid.This paper systematically studied the effects of BBG on the properties of wheat flour and wheat dough, and further explored the interaction between BBG and the main componments in wheat flour(starch and gluten), and finally investigated the effects of addition of 1.0%BBG on the quality of steamed bread.Firstly, effects of BBG on the properties of wheat dough were evaluated with Rapid visco-analyzer, Mixolab mixer, rotational rheometer and fourier transform infrared spectroscopy. Results showed that the wet gluten content reduced significantly(p<0.05). The peak, trough, breakdown and final viscosities increased with the rise of BBG content, while the setback value gradully decreased. Addition of BBG gradually increased the water absorption of wheat dough from 58.1% to 60.7%. However, the development time, dough stability, weakening value and back value had shown a decreasing trendency. The presence of BBG could reduced the elastic modulus and the viscous modulus of wheat dough. Fourier infrared spectra results indicated that the addition of BBG had induced the redistribution of bound water in the dough system. The gluten secondary structure had also changed, theβ-turn ratio decreased from 34.75% to 32.79%, while the β-sheet ratio and random structure ratio increased.Secondly, the influence of BBG on the pasting, rheological and retrogradation properties of wheat starch was investigated and the interaction between wheat starch and BBG was studied with High Performance Size Exclusion Chromatography. Results showed that addition of BBG induced a significantly increase of pasting viscosities and the amount of leached amylose(p<0.05). Higher elastic modulus and viscous modulus of pastes were also observed, indicating that BBG promoted the swelling and pasting process of wheat starch.The gel hardness and retrogradation enthalpy decreased during the storage time. It showed that the mixture could form more compact and uniform structure when stored at 4℃ for 14 days, demonstrating that the long-term retrogradation of wheat starch was evidently inhibited in the presence of BBG. From the molecular weight distributions results, it could be seen that the average weight molecular of amylose was significantly increased while no apparent changes in the weight molecular of amylopectin were observed(p<0.05).Then, based on the measurments of water binding capacity, rheological properties, freethiol content and gel electrophoresis, effects of BBG on gluten were studied. Addition of BBG had increased the water binding capacity of gluten and decreased elastic modulus and viscous modulus of gluten ball. Meanwhile, the free thiol content gradully increased. The gel electrophoresis results showed that the gluten structure was more unstable in the presence of BBG, and more gliadin aggregation could be extracted by SDS while the molecular distribution of glutenin showed no differences under reducing conditions.Finally, 1.0% BBG was added into wheat flour to prepare steamed bread and the specific volume, gas cell characteristic, texture properties and sensory scores of steamed bread during cold storage were evaluated. It demonstrated that the specific volume showed no significant changes with the addition of 1.0% BBG(p﹥0.05). The gas cell number decreased from 4245 to 2891, and the average gas area increased from 62.83 mm2 to 87.03 mm2. Compared with the control steamed bread, addition of 1.0% BBG significantly reduced the hardness and resilience of steamed bread during the storage time(p<0.05), indicating that BBG could effectively promote the storage quality of steamed bread. The sensory scores of 1.0% BBG steamed bread were lower than the control steamed bread before the cold storage, but higher during the cold storage.