Influences On The Production Quality Of Traditional Steamed Bread With Different Processing Degree

In this study, eleven wheat flour with different processing precision were made up by the material of four basic flour, bran, and germ, and the impact of the processing precision on the quality and flavor in traditional flavor steamed bread along the whole making process was investigated. First, the characteristics of flour and dough were measured to study the relationship among processing precision, flour quality and dough characteristics.Then,through making and detecting quality standard of steamed bread, such as fermentation characteristics, color grade, texture, sensory evaluation and so on,the quality differences were investigated and the relationship among processing precision, starter culture and quality of the steamed bread were pointed out definitely. In addition, wheat flour with yield of 40%,60%,100% was selected to analyze the influence of processing precision and starter culture on composition and content of volatile flavor, exploring the variety reason of volatile compounds.Finally, the trends and relationships that acidity and content of organic acid produced in the fermentation process were compared between yeast starter dough and traditional Laojiao starter dough,and biochemical reactions and mechanisms in the fermentation process were investigated. The experimental conclusion was as follows:1. The basic indicators of wheat flour with different processing precision were studied,and results indicated that: With the decrease of processing precision, the content of ash and crude protein was increased significantly. Meanwhile, the content of crude starch and falling number were reduced obviously, and wet gluten content increased firstly and then decreased.Both the color value and whiteness of flour were degraded, and the flour turned to become yellow and red. As the flour yield was exceeded to 80%, bran speck of flour was increased as sharply as black dot area of flour. As for solvent retention capacity, the solvent of distilled water, sodium carbonate, sucrose showed an increasing trend, while the retention capacity of lactic acid was decreased obviously. This appearance indicated that the content of pentosan was increased, the characteristic of gluten was deteriorated, the content of damaged starch was raised, and flour retention capacity of water was improved.2. The properties of dough with different processing precision were analyzed, and results were as follows: The decrease of processing precision caused negative impact on the gelatinization property of flour. As for farinograpH?tensile properties and bubble consistency properties, when the flour yield was 50%~76%, the dough had a lot of features, such as good viscoelasticity, long formation time, high stability, low degree of softening and high flour quality index. The dough not only had large stretching area, but also good extensibility and stretchability, which were in favor of volume increasing and retaining of dough. When the flour yield was exceeded 80%, tensile properties of dough was decreased, toughness became large, ductility was poor, and this indicated that addition of bran brought negative impact on the dough property of starch. As the raise of flour yield, fermentation time T1 increased,fermentation expansion height Hm decreased, and(Hm-h)/Hm also declined. Moreover, the present time for the dough hole Tx decreased, the total volume of gas release reduced, and retention coefficient R decreased. The gas holding strength was weak, the fermentation process slowed down, and the dough was easy to leak gas. With flour yield of 60%,performance of fermentation characteristic was the best, but performance of fermentation characteristic was declined obviously as the flour yield exceeded 80%. In summary, when the flour yield was greater than 80%, the qualities of the dough became worse obviously, which brought negative impact on the quality of flour products.3. With the decrease of the flour processing precision, the colour grade,specific volume and sensory evaluation of steamed bread became poor, the height to diameter decreased firstly and then increased. As for textural properties, hardness, viscosity, plastic viscosity and chewiness increased overall, while elasticity, cohesion and response values decreased. When steamed bread were made with wheat flour yield of 40%~76%, the color grade, specific volume, height-diameter ratio changed slowly, and sensory evaluation score were high.However the color grade, specific volume and sensory evaluation decreased sharply, while height-diameter ratio increased as the flour yield was exceeded to 80%. Compared steamed bread made of yeast with Laojiao, the sensory evaluation score had no apparent differences,and they had their advantages and disadvantages in quality respectively. The specific volume,4. color, softness of steamed bread made of Laojiao were inferior to steamed bread made of yeast, but the steamed bread made of Laojiao had better appearance, close structure,chewy,better flavor and taste.5. The volatile compounds was analyzed:With the decrease of the processing precision,the volatile compounds of flour, dough, steamedbread were increased obviously. The kind of volatile compounds in Laojiao production process was higher than that in yeast production process with the same processing precision, which meaned Laojiao starter made the flavor more full-bodied.The result, in a manner, indicated that the microbial activity,metabolism and flavor compounds generation influenced by the processing precision of flour and type of starter cultures. In the process of making steamed bread, volatile compounds were different from flour, dough to steamed bread. The major volatile compounds in flour were aldehydes, alcohols, hydrocarbons, benzene substances. While the major volatile compounds in dough were alcohols, esters, benzene, aldehydes, and ketones. The major volatile compounds in the steamed bread were hydrocarbons, alcohols, aldehydes and esters in turn.6. The acidity and organic acid content were analyzed in the fermentation process of dough: With the increase of fermentation time, the acidity of fermentation dough went up, the content of main organic acid such as lactic acid and acetic acid also showed an increasing trend. The acidogenic ability and content of lactic acid,acetic acid from Laojiao fermentation dough were stronger obviously than that from spontaneous fermentation dough and yeast fermentation dough. With the decrease of processing precision, the pH and TTA of dough showed an increasing trend, and the content of lactic acid also increased significantly, while the content of acetic acid didn't show an obvious law.