Study,on,the,Quality,Evaluation,of,Steamed,Bread,and,the,Physical,and,Chemical,Properties,of,Wheat
Fenglan ZHANG Chengmei WANG De LI
Abstract In this study, the different physical and chemical properties of wheat were studied, and on this basis, and the quality of steamed bread made was evaluated. We analyzed the correlation between the evaluation indexes of steamed bread and the basic physical and chemical indexes of wheat, and investigated important factors that affect the evaluation indexes of steamed bread, including flour extraction rate, protein content, amylose content, protein, added amount of yeast, fermentation time and other aspects. According to the study results, it was shown that different factors had different effect on steamed bread quality, with both positive correlation and negative correlation.
Key words Steamed bread quality evaluation; Wheat physical and chemical properties; Correlation analysis
Received: December 5, 2020 Accepted: February 23, 2021
Fenglan ZHANG (1978-), female, P. R. China, assistant engineer, devoted to research about Physical and Chemical indexes of wheat flour.
*Corresponding author. E-mail: 187387656@qq.com.
China has a vast land and abundant resources, and the wheat planting area accounts for about 17% of all cultivable areas in the world［1］. The varieties of wheat are very different, and the quality of wheat is also different. Wheat occupies an important position in Chinas grain production and is the second largest type of grain in grain production following rice. Steamed bread made from wheat occupies a very important position in Chinas traditional food culture. It is known as "Oriental Hamburger", and is an essential food for ordinary people, especially those in the north. The quality of steamed bread directly determines the taste buds of the people, and determines the quality of life of thousands of people. The current methods for evaluating the quality of steamed bread mainly come from the steamed bread production method and evaluation system in SB/T 10139-93 Steamed bread flour product standard issued by the Ministry of Commerce in 1993. This standard has been published for nearly 20 years. With the development of the economy, many contents have not kept up with the times. Meanwhile, the standard is affected strongly by subjective factors, and is quite different from the current steamed bread production process, so it can not reflect the quality of steamed bread. This study was in line with previous studies and analyzed the factors that affect the quality of steamed bread, with an attempt to obtain a newer judgment basis that can better reflect the quality of steamed bread. In fact, there are many factors affecting the quality of steamed bread, such as protein content, starch content in wheat flour, appraisers, flour extraction rate, wheat varieties, wheat storage time, addition amount of yeast and fermentation time. This study mainly started with the analysis of the main influencing factors.
Effect of Flour Extraction Rate on the Quality of Steamed Bread
The flour extraction rate is an important indicator reflecting the quality of flour, as well as an indicator used to measure the processing precision of flour. It not only affects the texture and structure of wheat endosperm, but also affects the quality of flour. The flour extraction rate of wheat is related to crude protein, ash, moisture, and wet gluten. With the increase of flour extraction rate, crude protein and ash are positively correlated, while moisture is negatively correlated, and the wet gluten content first increases and then decreases. Meanwhile, the flour extraction rate is also related to whiteness, specific volume, hardness, elasticity, cohesiveness, and biting type. With the increase of flour extraction rate, the mixing of wheat bran into flour results in the deterioration of the gluten protein network structure［2］, which also causes a certain degree of damage to the quality of steamed bread. With the deterioration of the network, the hardness and biting type of steamed bread increase, and the resilience decreases［3］. Therefore, different levels of flour extraction rate have a greater impact on the quality of steamed bread. Only by comprehensively considering various factors to determine the best flour extraction rate can higher-quality steamed bread be obtained. In this study, the excellent wheat variety Jimai 22 in Shandong area was selected as an example for research. The specific data are as follows.
Table 1 shows that the flour extraction rate was in the range of 35%-70%, and the specific volume, hardness, elasticity, cohesiveness, adhesiveness, biting type and resilience of steamed bred had little differences. When the flour extraction rate was in the range of 70%-97%, the adhesiveness and biting type of the steamed bread increased, but the cohesiveness and resilience decreased. The conclusions drawn from these data are similar to the results of previous studies.
Effect of Wheat Starch Content on Steamed Bread Quality
There are two types of starch, namely, amylose and amylopectin. In natural starch, amylose accounts for about 22%-26% and is soluble, and the rest is amylopectin. Although amylose occupies a small proportion, it occupies a relatively large proportion of the factors affecting the quality of steamed bread, and the effect is negative. Studies have shown that a higher ratio of amylopectin to amylose and a higher content of damaged starch have a better effect on the quality of steamed bread［4］. Steamed bread made from wheat with high amylose content has poor quality, poor elasticity and high viscosity, while steamed bread made from wheat with low amylose content has good elasticity, high quality and low adhesiveness. The higher the starch content, the worse the quality of steamed bread［5］. Wang et al.［6］ pointed out that amylose content is negatively correlated with the volume, specific volume, height and sensory score of steamed bread. The ratio of amylose to amylopectin in wheat starch is also an important factor affecting wheat quality. The proportion of amylopectin in wheat was about 3/4, and was positively correlated with the volume, specific volume, and height of steamed bread, as shown in Table 2.
From the data, it can be seen that the content of amylose in wheat was negatively correlated with specific volume, appearance, color, elasticity, and adhesiveness, and positively correlated with hardness, fracture, gumminess, biting type and resilience.
Effect of Wheat Protein on the Quality of Steamed Bread
The protein in wheat can account for about 11%, and its protein mainly includes leucosin, globulin, gliadin and glutenin, etc., the effects of which on wheat processing quality are very different［7］. Studies have shown that wheat albumin is significantly or extremely significantly negatively correlated with gluten and dry gluten content. Gliadin and glutenin are the main components of gluten. The quantity and ratio of the two determine the quality of gluten. Gliadin is rich in viscosity, ductility and swelling. Glutenin determines the elasticity of gluten. Its contents and quality in flour and gluten are related to the quality of steamed bread. There was a significant positive correlation between glutenin and volume and score of steamed bread. There is a large amount of residual protein in wheat that cannot be dissolved by water, salt, ethanol or dilute alkali. There is a good positive correlation between the amount of residual protein, and dough strength and steamed bread quality, which has an important influence on the quality of wheat varieties. The research on protein in this study referred to previous studies and literatures, and no specific research was done on specific data.
Effect of Hard and Soft Wheat on the Quality of Steamed Bread
Generally, wheat with a lot of protein is called durum wheat, which has high bulk density, more gluten, high quality of flour, and good palatability, and is suitable for all kinds of cooked wheaten food. On the contrary, soft wheat (starchy wheat) has more starch, less protein, soft texture, less gluten, slightly poorer flour quality, poor palatability, the made cooked wheaten food is too soft, and the steamed bread made is easy to crack. Durum wheat mainly includes hard white winter wheat, hard red winter wheat and hard red spring wheat. These types of wheat contain relatively high protein content, which means that more gluten can be formed. Durum wheat flour includes bread flour, gluten flour, and some whole wheat flour. Soft wheat includes soft white winter wheat and soft red winter wheat, which are suitable for making foods that do not require excessive fermentation and expansion, such as cakes, biscuits and pie crusts. Soft wheat flour includes cake flour, pastry flour, etc. Theoretically, the steamed bread made from high-quality wheat has better texture and elasticity than that made from wheat with less gluten and low protein quality. Therefore, durum wheat with more gluten content is generally selected when making steamed bread.
Effect of the Addition Amount of Yeast on the Quality of Steamed Bread
Yeast plays a very important role in the process of making steamed bread as it is the most important microbial starter and biological loosening agent［8-9］. It can be said that steamed bread cannot be made without yeast, but the amount of yeast added is an important factor that affects the quality of steamed bread. In this study, different amounts of yeast were added to wheat. Steamed bread was made into a height of 6 cm according to the requirements to observe its height, elasticity, smoothness and resilience. The specific data is shown below.
In this part, a single variable was determined, that is, the amount of yeast added. The steamed bread dough of the same volume was made at the same time, and the heights of the steamed bread obtained according to the different amount of yeast added were measured, while testing the elasticity and resilience by pressing with thumbs and observing the smoothness. Finally, it was finally determined that the height, elasticity, smoothness and resilience of steamed bread were the best when the added amount of yeast was 0.8%.
Effect of Fermentation Time on the Quality of Steamed Bread
Although the amount of yeast added is appropriate, the dough will become sour if the time is not well controlled, and the taste of such steamed bread is extremely bad. Therefore, the fermentation time is also something we need to control. This study based on the principle of single variable, used fermentation time as a variable and made steamed bread under the conditions of the same flour and the same yeast content. Under the evaluation of the tasters, the steamed bread was scored according to the taste, viscosity, etc., with a full score of 10. The specific scores are shown in Table 4. Table 4 shows that when the fermentation time was about 45 min, the steamed bread was the best in terms of volume, viscosity, and taste.
Conclusions
The evaluation of the quality of steamed bread was mainly in accordance with the steamed bread production method and evaluation system in SB/T 10139-93 Steamed bread flour product standard issued by the Ministry of Commerce in 1993. This standard cannot meet the current evaluation of steamed bread for a long time, so the development of a new evaluation standard should be put on the agenda. This study analyzed the current factors that have a greater impact on the quality of steamed bread, and analyzed factors such as flour extraction rate, protein content, amylose, hard or soft wheat, added yeast, and fermentation time. Studies have shown that when the flour extraction rate was about 80%, its specific volume, elasticity, hardness, cohesiveness and resilience should all be optimal. The content of amylose in wheat was negatively correlated with specific volume, appearance, color, elasticity and adhesiveness, and positively correlated with hardness, fracture, adhesiveness, biting type and resilience. The content of protein is mainly related to the type of proteins contained, which is not much researched. Durum wheat has a greater impact on the quality of steamed bread than soft wheat. Yeast is a biological leavening agent that must be added in the process of making steamed bread. Its addition amount and fermentation time directly affect the quality of steamed bread. It was determined by experiments that the steamed bread made when the addition amount was 0.8% and the fermentation time was 45 min was the best. Therefore, only by comprehensively considering various factors can the quality of steamed bread reach the best.
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