The quality of wheat flour includes food quality and nutritional quality. The food quality is divided into baking quality, cooking quality, etc., and is evaluated by the appearance, color, structure, texture, texture, smoothness, mouthfeel, elasticity, toughness, viscosity, odor and other quality indicators of the food.
Wheat flour quality
In general, the main factor affecting the taste and texture of the edible quality of wheat flour is the quality of the raw material itself, and the processing technology also has a certain influence on it. The processing technology can control the thickness of the wheat flour, and the thickness includes the problem of the damaged starch content. Sometimes, some flour mill products may have problems such as sticky hair, shrinking after cooling, and darkening of the noodles after cooling. There are many reasons for this phenomenon. The fineness of wheat flour and the high content of damaged starch are one of the reasons. The grain size of wheat flour is too fine, and the damage of starch content is too high, which is caused by unreasonable process. The main effects of starch damage are: the water absorption capacity of the dough is increased, and the water holding capacity is decreased; the sensitivity to the enzyme is enhanced, and it is easily decomposed into dextrin. Factors affecting starch damage include raw materials, wheat flour thickness and the like.
The modern milling process has a distinct layering and stripping characteristics. Generally, vertical flow direction and light research subdivision are emphasized. The flour of each system comes from different parts of wheat endosperm, which can basically reflect the composition and properties of various parts of the endosperm. Based on this theory, this study used multiple online sampling to determine the distribution of protein, starch and related properties of protein and starch, and to find out the distribution of protein and starch in the endosperm. The wheat flour produced by food provides a theoretical basis.
1, the amount of protein
The protein and wet gluten content of domestic medium-gluten wheat and mixed high-gluten wheat were the highest in the outermost skin milling powder (IV Bc and VB, respectively) (21.15%, 45.91% and 14.22%, 44.65%, respectively). The lowest is IS or 1Mc, and the highest is nearly 2 times the lowest. In the entire powder path system, IV Bc and VB powders are the powder closest to the cortex and the aleurone layer, and the IS and 1Mc powders are the powder closest to the central portion of the endosperm. This indicates that in wheat endosperm, the protein content closest to the cortex is the highest, and the protein content in the inner part of wheat endosperm is the lowest. It can also be seen from the table that the distribution of flour protein in other systems decreases from the outer layer to the inner layer (IIIB, II B, IB), and the heartbeat system also has a higher protein content in the cortex.
2, dough rheological properties
(1) Water absorption rate. The test results showed that for the water absorption rate, the test samples of the two wheat skin grinding and heart-grinding systems all had the trend increasing trend, and the highest value appeared in the last heart-grinding system (7, 8M and 6M). The reason is that the closer to the cortex, the higher the protein content of the sample and the higher the water absorption capacity; the other reason is that the higher the starch content of the damage, the higher the water absorption rate.
(2) Dough formation time and stabilization time. From the average of dough formation time and stabilization time: the average time of formation of domestic medium-gluten wheat skin grinding system is 5.28 min, the average stability time is 8.6 min, and the mixed high-gluten wheat is 6.09 and 9.91 min respectively; The average formation time of medium-gluten wheat heart mill and slag grinding system was 2.25 min, the average stability time was 5.40 min, and the mixed high-gluten wheat was 3.97 and 7.59 min, respectively. It can be seen that the overall evaluation of the fur mill system is superior to the heart mill and slag mill system. The lowest formation time of domestic medium-gluten wheat appeared in IB, and the stability time of 1M and 1T was also shorter. Both IB and 1M powders are from the center of the endosperm, indicating that the flour content of this part is low and the quality is not ideal. The system with high formation time and stable time, domestic medium-gluten wheat appeared in the middle and rear road skin grinding system (IIIB, IVB), mixed high-gluten wheat appeared in the middle and rear road skin grinding system (IIIB, IVB), rescreening system The anterior heart-milling system has a maximum at IIIB and IV, which indicates that the endosperm close to the outer layer of wheat has higher protein content and better dough characteristics.
(3) Degree of weakening. The closer the skin grinding system is to the cortex, the weaker the degree of weakening of the heart grinding system.
(4) Tensile test results. From the tensile curve analysis, the average value of the tensile curve area of the domestic medium-gluten wheat skin grinding system is 85cm2, the average tensile resistance is 231.4 EU, the average elongation is 189.4 mm, and the average stretching ratio is 1.80, while the mixing is high. The indexes of gluten wheat were 116. 1 cm, 236.9 EU, 212 mm and 1.14 respectively. The average value of the tensile curve area of the domestic medium-gluten wheat heart-grinding system was 62 cm2, and the average tensile resistance was 278.2 EU. The average elongation was At 132.9 mm, the average stretch ratio is 2.6, while the indicators for mixed high-gluten wheat are 77 cm2, 230 EU, 172.3 mm, and 1.3, respectively. On the whole, the average value of the tensile curve area and elongation of the skin-grinding system and the heart-grinding system of imported high-gluten wheat were higher than those of domestic medium-gluten wheat.
From the data of each system, the comprehensive evaluation of the tensile results of the two groups of samples has good results at IIIB, which is consistent with the results of silty determination; from the distribution of the comprehensive evaluation data of each system, the skin grinding system IB ~IIIB has a trend of increasing channel by direction, while the heart-grinding system has a trend of weakening channel by channel.
3. Starch distribution and gelatinization characteristics
The starch content, amylose content and gelatinization properties of wheat starch have a great influence on the quality of the noodle products. Studies have shown that the starch content, amylose content and gelatinization characteristics of wheat endosperm are mainly related to wheat varieties and planting environment. By measuring the starch and amylose content and gelatinization characteristics of different samples of wheat endosperm, the author aims to understand whether the distribution of amylose content and the gelatinization characteristics of wheat endosperm are regular.
4, starch and amylose distribution
The skin grinding system has a tendency to gradually decrease the total starch and amylose content of B-IVB. In the heart-grinding system, the total starch and amylose content of lM-8M powder also tends to decrease. Among the powder paths, IV and 8M powders are the closest to the wheat cortex and have the lowest amylose content. Therefore, it can be inferred that in the wheat endosperm, the closer to the skin layer, the lower the amylose content. The linear correlation analysis of the above results showed that the results of skin grinding and heart grinding were significant, which indicated that the distribution of total starch and amylose content in wheat endosperm had certain regularity.
5, pasting characteristics
The gelatinization temperature of wheat starch is below 63 ° C, which is consistent with previous studies. The viscosity values of the various system samples are not the same, and there are large differences. In the skin grinding system, the viscosity values of IB, IIB, and IV showed a downward trend, and the viscosity of the IIIB powder sample was higher. In general, the viscosity value of the whole skin grinding system has a certain downward trend. The same analysis was performed on the heart mill system. The viscosity value of the IM coarse powder sample is the largest, the viscosity value of the 7 and 8M powder samples is the smallest, and the viscosity value of the IM～8M powder sample is decreasing. By performing regression analysis on the above results, the linear correlation is significant. Therefore, it is inferred that in the wheat endosperm, the powder sample closer to the cortex has a smaller viscosity value.
6, flour extraction rate and flour quality
The flour extraction rate of the milling process can be artificially controlled, and different flour extraction rates will exhibit different quality characteristics. In this test, the flour of each system was obtained on the production line, and the bran and the secondary powder were repeatedly powdered. The flow rate of each system was sequentially arranged, and the mixed powder was 50%, 55%, 60%, and 65%. 70%, 72%, 74%, 76%, 78%, 80%, 85% of each sample.
The increase of the water absorption rate of the dough is more obvious with the increase of the flour extraction rate. This is because as the powder extraction rate increases, the content of the outer endosperm (the posterior system powder) increases, the protein content also increases, and the natural water absorption rate increases. The back-end system also has a higher starch content in the powder damage, which also increases the water absorption rate of the dough.
It can be seen that the dough formation time and the quality index of the powder increase with the increase of the powder yield, and the degree of weakening is opposite. In terms of stabilization time, when the flour extraction rate is between 50% and 70%, the stabilization time decreases with the increase of the powder extraction rate, but there is the highest peak near 75%. Except for a peak near 75%, there is no obvious law. .
In the tensile test, the tensile resistance and maximum tensile resistance of the dough tend to decrease as the powder yield increases, while the elongation is reversed, but this trend is not obvious. The stretching ratio has a tendency to decrease with increasing powder yield, but there is a significant peak near the powder extraction rate of 75%. This phenomenon needs further study.
In the processing of flour, a test is still required: to test the content of magnetic metal in flour. This test has a standard "GB/T 5509-2008 grain and oil inspection, powder magnetic metal determination", when the tester is on a project It is generally measured by instruments, and there is almost no manual measurement. When it comes to instrument measurement, it has to be mentioned: magnetic metal analyzer. It is a special instrument for testing the content of magnetic metal in powdered food developed according to the latest national standard GB/T 5509-2008. This instrument is easy to operate and easy to use, in quality supervision, flour processing, grain storage and transportation, purchase and sales, scientific research, etc. The department is widely used.