Effects Of Sheeting Conditions On The Properties Of Chinese Steamed Bread

In the production of Chinese steamed bread, the sheeting of the dough has played an very important role. The changes of sheeting process could lead to a varieties of differences of steamed bread. Based on the single factor experiments which we’ve determined the best conditions of mixing dough with 3 different kinds of flour, we chose medium strength flour and designed different levels of sheeting times, folding methods, roll gap width, chiangmian quantity to study the effects of sheeting conditions on the basic qualities of steamed bread. By response surface experiments, the specific effects laws of sheeting conditions on the inflation properties, extending properties, continuous fermentation properties and TPA properties of steamed bread were discussed. The interactions of all the conditions were considered, either. The results of above experiments were validated by slice staining micro-graphy and SEM. Finally, we briefly analyzed moisture distribution differences caused by sheeting times. Main results were as following.(1)Low strength flour(LSF), medium strength flour(MSF), high strength flour(HSF) required different dough mixing processes. With the water of 30 degrees Celsius,addition of 42 percent, the best mixing time of LSF was 5-10 min, that of MSF was 15-20 min, that of HSF was 20-25 min. Steamed bread made with MSF had the highest sensory scores.(2)In terms of sheeting conditions,single-factor tests showed that sheeting 25 times, 45-degree or 90-degree folding methods, roll gap of 14 mm, 1% chiangmian quantity would lead to a larger specific volume, a higher whiteness and a lower hardness.(3)According to the RSM results, during the inflation, tolerable stress and the extensibility would be affected by the factors in the descending order as folding methods, sheeting times, chiangmian quantity, roll gap width, while that of the whole strength as folding methods, chiangmian quantity, roll gap width, sheeting times.(4)According to the RSM results, during the extending, tolerable stress would be affected by the factors in the descending order as folding methods, roll gap width, chiangmian quantity, sheeting times, while that of the extending distance as sheeting times, folding methods, roll gap width, chiangmian quantity. There were significant interactions between sheeting times and folding methods. In general, sheeting 31 times, 11 mm roll gap width, 45-degree folding, 0.79% chiangmian quantity would result in a balance of extending properties.(5)According to the RSM results, during the fermentation, the maximum height and the volume stability of dough would be affected by the factors in the descending order as sheeting times, folding methods, roll gap width, chiangmian quantity, that of the gas capacity as folding methods, sheeting times, roll gap width, chiangmian quantity. There were significant interactions between sheeting times and folding methods. In general, sheeting 23 times, 17 mm roll gap width, 90-degree folding, 0.60% chiangmian quantity would lead to a relatively better fermentation properties.(6)According to the RSM results, the springiness of steamed bread would be affected by the factors in the descending order as folding methods, sheeting times, roll gap width, chiangmian quantity, while that of the cohesiveness as folding methods, roll gap width, ciangmian quantity, sheeting times. The factors which affected the chewiness were complex, and there were significant interactions among all the four factors. In general, mezzo sheeting times and roll gap width, multiaxial folding methods, lower chiangmian quantity would result in higher springiness and chewiness, lower cohesiveness.(7)By slice staining micro-graphy and SEM, we observed that appropriate sheeting times and roll gap width could make the gluten network expend fully and stably. Lack of sheeting or excessive sheeting might destroy the gluten network. Uniaxial sheeting made he gluten expend in a parallel way, while multiaxial sheeting made the network uniform. Excessive chiangmian would result in a network destroy by starch granule.(8)According to the NMR experiments, sheeting 15 times led to a high level of free water and loose bound water quantity in the dough, and a low strong bound water quantity. Sheeting 25 times made strong bound water more, and both free water and loose bound water less. Sheeting 35 times made strong bound water keep in high level, while some of loose bound water become free water.In general, sheeting process had strong effects on properties of dough and streamed bread. We could change the sheeting conditions to control the quality of steamed bread, for there might be different requirements in different situations.