| In order to provide some related theoretical basis for the industrial production of Jiaozi sourdough steamed bread, firstly, the influence of making condition of sourdough on the biochemical indexes of the dough during the fermentation process was studied and the variation of corresponding index in the process was explored. On this basis, the effects of fermentation conditions: the fermentation time of sourdough, the add amounts of Jiaozi, fermentation temperature on the quality of steamed bread were studied, and the optimal fermentation condition of sourdough was optimized and determined with the response surface method. Then, the flavor properties of different steamed bread samples were analyzed by electronic nose and GC-MS technology in order to provide some reference for further flavor research and analysis of traditional flavor steamed bread. Finally, the effects of sourdough on the dynamic rheological properties of dough and the quality of steamed bread were studied. The main results of the study were as follows:Jiaozi add amounts and fermentation temperature were set as single variable factors, measuring the change of biochemical indexes during the long-time fermentation of the dough. When Jiaozi add amounts changed, add amount of jiaozi was 3%-5%, yeast and lactic acid bacteria contents were relatively high; Under different add amount conditions, and after fermenting for 15 h, pH value remained constant between 3.79 to 4.01, TTA also tended to be stable; Under different add amount conditions, water activity of the sourdough showed waving change trend; There were no significant variations in moisture content of the sourdoughs with different jiaozi add amounts; When fermentation temperature changed, as fermentation temperature varied from 25?-35?, yeast and lactic acid bacteria in the sourdough had good growth momentums and a large number of quantities; The higher the fermentation temperature was, pH value decreased sooner, TTA value increased more quickly, but during post-fermentation period, pH and TTA value tended to be stable; At different fermentation temperatures, the water activity was presented waving change, but the overall change showed downward trend; The moisture content changes of the sourdoughs fermented in different fermentation temperatures differed from each other,and there was no obvious regularity.The fermentation time of sourdough, Jiaozi add amounts and fermentation temperature were set as single factor variables, seeking for the effects of fermentation conditions on the quality of steamed bread, and optimizing the conditions. In the single factor test, when fermentation time varied from 15 h to 30 h, height-diameter ratio of steamed bread was relatively bigger, and specific volume was relatively larger. When fermentation time was in the range of 10 h to 25 h, bread had a better color, the whiteness of bread core and skin were higher. When fermentation time changed from 15 h to 40 h, bread had a better texture quality. When fermentation time changed from 15 h to 25 h, the sensory score of bread was higher. When Jiaozi add amount was 3%, bread had the biggest specific volume and a higher height-diameter ratio. When added amount was within the range of 1% to 3%, bread had a better whiteness. When add amounts was 3% and 9%, the samples had a similar, better texture quality. When the dosage varied from 1% to 5%, there were better sensory score for breads. When fermentation temperature changed from 25? to 30?, there was bigger specific volume and smaller height-diameter ratio. During the whole study scope of 20? to 40 ?, with the temperature rose, the whiteness of bread skin and core showed decreasing trend. When fermentation temperature ranged from 25? to 30?, we would get a relatively better texture quality, At the same time, there was a higher sensory score of bread. Optimizing and verificating the making process of Jiaozi sourdough steamed bread by response surface method, we found that the optimum process conditions were fermentation time 21 h, Jiaozi add amounts 4%, fermentation temperature 27?.There were 15 kinds of common flavor compounds in all samples, including 5 kinds of alcohols, 5 aldehydes, 2 esters, 1 benzodiazepines, 1 heterocycles and 1 condensed ring compounds, the ethanol content was the most. The variety and content of flavor compound in the steamed bread fermented by mixed fermentation agent was higher than the single yeast agent one, especially about alcohols and esters. Sourdough fermentation could improve the type and content of the bread flavor substances. Edible alkali added caused the reduction of type and content of bread flavor substances to a certain degree, obviously in aldehydes, ketones, esters, acids. But the base would lead to the generation of new substances, such as formic acid hexyl acrylate, 4-vinyl-4, 5-dihydro-pyrazol-3H-. All these factors, such as difference of fermentation agent and fermentation methods and edible alkali added, would impact bread flavor to some extent. The flavor difference between fresh yeast bread and other bread samples was most obvious, and sourdough fermentation could improve bread flavor, Effect of edible alkali on Jiaozi bread flavor was greater than its effect on yeast bread.Sourdough added in dough changed the viscoelasticity of dough obviously. Under the frequency scan mode, with the proportion of sourdough added increasing in the dough, the elastic modulus and viscous modulus of dough would reduce and the loss factor would increase, indicating that the dough intermolecular crosslinking system was weakened and the quantity of polymer reduced. Under temperature scanning mode, with the proportion of sourdough increasing, the gelatinization of starch was delayed, but the process time was shortened, and the end temperature was decreased. The right amount of sourdough added in the dough could improve specific volume of bread and bread color, and assure the texture and sensory quality of steamed bread. In general, when sourdough dosage changed from 20% to 60%, steamed bread showed better quality. |
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