Analysis Of Wheat Quality Properties And Constructing For Evaluation System Of Steamed Bread Of Guanzhong Area In Shaanxi Province

In order to master wheat quality of field production in Guanzhong region of Shaanxi province, and improve techniques of quality analysis and evaluation of steamed bread, 92 wheat samples were taken as materials in Guanzhong region of Shaanxi province in 2008. On the basis of systematic analysis of grain physical quality, milling quality, protein quality, starch quality, dough rheological properties of wheat and edible quality of steamed bread, key indexes of wheat quality and production area of high quality wheat in Guanzhong region of Shaanxi province were determined, and this study was also to determine key indicators of steamed bread quality by combining sensory evaluation index, chroma meter index, and texture analyzer index. Evaluation system of steamed bread quality was constructed. Main test results were as follows:Test weight, grain hardness and protein content of wheat cultivars of field production in Guanzhong region of Shaanxi province were higher, but sedimentation value was lower, protein quality was poor, and general in rheological properties of dough. 15% wheat samples of field production reached the national standard of strong gluten wheat, 9% reached the national standard of weak gluten wheat, and other 76% were middle gluten strength wheat.In the three areas of Guanzhong region of Shaanxi province, wheat from Weinan area was higher in flour extraction, better in flour's color and gluten protein quality, but lower in grain protein content, the performance of farinograms and extensographs of dough were excellent. In Xianyang area, 1000-grain weight, test weight and grain color of wheat were more balanced, flour extraction, sedimentation value and protein content of wheat was lower, flour ash content, wet gluten content and gluten index was higher, farinograph parameter was excellent, extension of dough was small but more flexible. In Baoji area, grain hardness and test weight of wheat were relatively low, grain protein content was higher, but gluten protein quality was poor, the performance of farinographs and extensographs of dough was general.29 indexes of wheat quality properties can be compressed into seven common factors, namely protein quality factor, quality processing factor, starch pasting properties factor, gluten quantity factor, wheat physical quality factor, starch hot paste stability factor and starch setback factor. The accumulative variance contribution was more than 82.14%. Cluster analysis was conducted according to 13 key quality properties, namely flour L*, ash content, protein content, water absorption, softening degree, valorimeter value, maximum resistance, extension area, peak viscosity, pasting viscosity at the beginning of constant phase at 93℃, pasting viscosity at the beginning of cooling phase, pasting viscosity at the end of cooling phase and break-down, and 92 wheat samples were clustered into three categories, namely wheat samples from the northern part of Sanyuan County, Jingyang county and Wugong county which were drought area can be attributed to one type had better farinograms, excellent extensograms and starch gelatinization viscosity properties; the wheat samples from Linwei county and Pucheng county can be attributed to a second type with excellent farinograms, better extensograms, and ordinary starch gelatinization viscosity properties; the third type was from Pucheng county, along the provincial highway to Fuping county, Sanyuan county, Jingyang county, Wugong county, Fufeng county, Qishan county, and Fengxiang county. This area include eight counties (districts) of Weinan, Xianyang and Baoji city. This area had better water-fertilizer conditions, high yield and good processing quality, but the performance of farinograms, extensograms and starch gelatinization viscosity properties was poor.Wheat grain physical quality and milling quality have effect on appearance traits and surface color of steamed bread, especially the appearance and formation of structure of steamed bread and finally affect the total score of steamed bread. Protein content and gluten quantity are beneficial to surface color of steamed bread, increase specific volume of steamed bread and improve internal structure, which affect the total score of steamed bread. Modest extensibility and flexibility meet requirements of high quality steamed bread. Peak viscosity, pasting viscosity at the beginning of constant, pasting viscosity at the beginning of cooling phase, pasting viscosity at the end of cooling phase and pasting viscosity at the end of constant phase at 50℃were closely related to color, elasticity and toughness of steamed bread. Specific volume is one of the most key index of steamed bread quality.Wet gluten content, extension energy, falling number, maximum resistance, test weight, break-down, hardness and water absorption influenced the specific volume of steamed bread, and the degree of the affect decreased in turn, extension area had the biggest influential effect for specific volume of steamed bread. There was a positive correlation between extension area and specific volume,the prediction effect of extension area for teamed bread quality was better.Based on evaluation system of steamed bread quality, the specific volume had highly positive correlation with hardness, gumminess, elasticity, resilience and chewiness of texture analyzer TPA testing, L* were highly positive correlation with surface color, extension rate had significant negative correlation with height, textural properties(hardness * gumminess * chewiness) were positively related to the appearance of characteristic and internal structure, odor was positively related to compressed relaxation properties (elastic* cohesive * reversibility). The specific volume, L*, extension rate, texture, compression relaxation, flexibility, adhesion were regarded as key indicators for quality evaluation of steamed bread. Based on the results of weight distribution of seven key indicators and using reference principle and method of appraisal of wheat cultivars and quality, evaluation system of steamed bread quality was that, specific volume is 25 points, L* is 15 points, textural properties is 10 points, adhesion is15 points, compression relaxation properties is 15 points, springis15 points, extension rate is 5 points, and total score is 100 points. 22 field production wheat samples in 2009 were used as verified materials, according to sensory score of SB/T10137-1993 standard and evaluation system of steamed bread quality, classification results are in agreement. Evaluation system of steamed bread quality objectively reflects the quality characteristics of wheat flour, and the evaluation results will be more reliable.