Chemical composition and properties of flour
(1) Moisture: national standard 13±0.5%
(2) Protein: 8-14%
Gladin: alcohol-soluble protein, pH 6.4-7.1
Glutelin: soluble in dilute acid or alkali, pH 6-8
Insoluble protein, accounting for 80 % Main component of gluten
Wheat globulin
Wheat albumin
Acid-soluble protein
Soluble in water and dilute hydrochloric acid solution , belongs to soluble protein
(3) Carbohydrates
Account for 70% of the weight of wheat kernels and 75% of flour, including starch, dextrin, cellulose, free sugar and amyl Polysaccharides
Soluble carbohydrates: refers to the portion of carbohydrates that can be digested and utilized by the human body, including starch, dextrin and free sugars. Starch is mainly in the endosperm, and sugar is in the germ and aleurone layer. These two types account for more than 70% of the wheat grain. Starch is the main component, and sugar accounts for about 10%. As the wheat grain matures, most of the sugar is converted into starch.
Wheat starch is composed of 19-26% amylose and 74-81% amylopectin. The former has 50-300 glucose groups and the latter has 300-500 glucose groups. Amylose is easily soluble in warm water and has almost no viscosity, while amylopectin is easy to form a sticky paste.
Crude fiber: Most of it is contained in bran and cannot be absorbed by the human body. It generally affects the quality of flour and should be removed during the milling process.
(4) Fat
Fat: It exists in the germ and aleurone layer, and the content is small, 1 to 2% in wheat. Although it is a nutritional component, it is mostly composed of unsaturated fatty acids. Easily oxidative rancidity causes flour or products to taste bad and is generally removed during the milling process. Flour contains less fat, less than 1%.
(5) Vitamins
Vitamins: Wheat contains more vitamins B1, B2, and B5, and also contains a small amount of vitamin E, vitamin A, and a trace amount of vitamin C, but does not contain vitamin D.
(6) Minerals
Minerals: measured by ash
Minerals (calcium, sodium, phosphorus, iron, etc.) exist in the form of salts. Most of the residue after complete combustion of wheat or flour is mineral salts, also called ash. 1.5%-2.2% in wheat kernels
There is very little ash in flour, and most of the ash is in the bran. Wheat flour is graded by ash, which indicates the degree of bran removal.
(7) Enzymes in flour
1. Amylase: α- and β-amylase, two important enzymes in baked goods. Beta-amylase is sufficient but alpha-amylase is deficient. A part of α-starch (dextrin) and β-starch can be hydrolyzed and converted into maltose, which can be used as the main energy source for yeast fermentation.
Beta-amylase is thermally unstable, and saccharification and hydrolysis occur during the yeast fermentation stage;
Alpha-amylase changes soluble starch into dextrin, changing the rheology of starch. It is relatively stable to heat and can still undergo hydrolysis at 70-75°C. The higher the temperature, the faster the action. Alpha-amylase greatly affects the rheology of dough during baking, and its role in the oven can greatly improve the quality of bread.
2. Protease: There are two types of proteases in flour. One is a protease that can directly act on natural proteins, and the other is a polypeptide that can re-decompose polypeptides, the intermediate products in the protein decomposition process. Enzymes. The main role in the stirring and fermentation process is protease. Its hydrolysis reduces the strength of gluten, shortens the dough kneading time, and makes it easy for the gluten to fully expand.
3. Lipase: This enzyme has little impact on the production of bread and biscuits, but it has an impact on prepared cake flour, because it can decompose the fat in the flour into fatty acids, which can easily cause rancidity. Shorten storage time.
The main components of flour are protein and starch. Flour is divided into several grades
Grade protein (%) minerals (%) type and use
Special flour 7.2 0.32 Low-gluten flour for snacks
First-class flour 12.7 0.43 High-gluten flour for bread
First-class flour 10.7 0.45 High-gluten flour for French bread
Second-class Flour 13.5 0.54 High-gluten flour for bread
Flour is ground from wheat. The wheat undergoes processes such as cleaning and removing impurities, moistening, grinding, and sifting to produce various grades of flour. It is divided into high-gluten flour, low-gluten flour and medium-gluten flour according to its protein content. Among these three types of flour, high-gluten flour requires protein above 11.5, medium-gluten flour generally between 8.5-11.5, and low-gluten flour below 8.5.
The chemical components of flour include protein, carbohydrates, ash, enzymes, moisture, fat and vitamins.
1) Protein, the protein content in flour varies according to different wheat varieties. Ranging from 6 to 20, it is mainly composed of five types: gliadin, glutenin, acid-soluble protein, albumin and glomerulone
2), carbohydrates, that is, sugars, in The highest content in flour is around 75, most of which is in the form of starch. In addition, there are small amounts of soluble sugar (such as glucose, fructose, sucrose, etc.), cellulose, hemicellulose, etc. in flour.
3) Ash content Ash content refers to the white powdery solid when bread is baked at high temperature. After the flour is grilled, the organic matter volatilizes and the inorganic matter remains, so the ash content is the inorganic mineral content in the flour.
4) Enzyme. Enzyme is a special protein and an indispensable catalyst in biochemistry. Flour only contains the following types:
①Amylase, which plays a very important role in bread making, can hydrolyze the dextrin and a very small amount of soluble starch in the flour into maltose, maltose Continue to convert into glucose to supply the energy needed for yeast fermentation
②Protein decomposing enzymes are generally found in very small amounts in flour, but they can be produced artificially
5), moisture, flour The moisture content in flour is specified to be between 12.5-14.5. When preparing the dough, the amount of water added should be determined according to factors such as the moisture content and gluten content in the flour. The moisture content of flour directly affects the water absorption of flour, so it also affects the quality of bread.
For different noodles, the flour required has different quality requirements (such as Table 3), flour protein and ash powder, flour adhesion characteristics and sometimes stability are the main specifications. Generally speaking, high flour protein will make the finished product elastic and stronger, but it will have a certain negative impact on the color and brightness of the noodles. Therefore, flour with optimal corresponding properties is required for each noodle type.
The ash content in flour is one of the important items when inspecting flour, because generally speaking, ash powder has a negative impact on the color of noodles. Most flours used to make noodles require an ash content of less than 0.5%, but the flour used to make high-quality noodles has an ash content of only 0.4% or less. However, the ash content is not always related to the color of the noodles.
The adhesive properties of starch are also an important aspect to investigate. Japanese and Korean noodles require high viscosity, and the maximum viscosity breaking point is 200Bu. However, for Chinese noodles, the viscosity is too high or too low, which will reduce the accuracy of the noodles.
Some rheological properties of dough are also included in the investigation specifications of flour, because they have an impact on the noodle making process and dietary quality. Stability time is the most common quality parameter for flour.
Starch is the main source of calories in people’s food and the main component of wheat flour. The viscosity of starch is related to the taste of noodles. If the viscosity is too high, the noodles will be damaged.
1 Starch quality has an important impact on the production of instant noodles. Impact
Starch is the main component of noodles. The edible state and properties of starch after gelatinization have a great impact on the quality of noodles. The production of glossy, soft and delicious noodles is directly related to the viscosity of the starch in the flour. The viscosity of the starch should not be too strong or too weak. If the viscosity is too strong, the noodles will be hard and have poor palatability; if the viscosity is too weak, the noodles will be brittle and loose, with poor luster and poor elasticity, and will also cause difficulties in noodle processing.
2 The impact of protein on the production of instant noodles
Protein content directly affects the water absorption of flour and the tensile strength of dough, and is the main indicator of flour for noodles. After the flour and water are fully mixed, the protein absorbs water and swells to form gluten. After several rolling processes, the gluten adheres to each other and surrounds the loose starch with a fine and uniform network in the dough sheet, eventually turning it into a wet dough with plasticity and elasticity. Noodle. Therefore, the protein content and quality of flour are the main factors affecting the intrinsic quality of noodles. If the protein content is too low, the ideal, fine and uniform gluten network structure cannot be formed, and the final product has low strength, is easy to break, and has poor intrinsic quality. If the protein content is too high, high-quality noodles cannot be made. Instead, the noodles will become darker, harder, less palatable, difficult to compound, and easy to break. For fried instant noodles, the noodles are required to be puffy after frying, rehydrate quickly and not rotten, which requires the use of flour with high protein content. At the same time, the protein in flour has an inverse relationship with the oil content of the product. That is, instant noodles with low protein content absorb more oil during the frying and dehydration process, resulting in a high oil content in the finished product; while fried instant noodles with high protein content have a lower oil content in the finished product. Relatively low, which not only reduces consumption but is also easy to preserve.
Flours with the same protein may not have the same wet gluten content. Important for improving noodle processing properties is the wet gluten content. For general fried instant noodles, the recommended wet gluten content is 30%-34%; for the production of hot-air dried instant noodles, the recommended wet gluten content is 28%-32%. In production, it is not enough to only emphasize the content of wet gluten. We must also pay attention to the quality of gluten. Even if there is a large amount of inferior gluten, it will not produce good noodles.
The quality of gluten is affected by many factors. The gluten quality of hard wheat is better than that of soft wheat. Flour milled from frost-damaged or insect-damaged wheat has poorer gluten quality. When wheat or flour is heated, the protein in it will be denatured, which will lead to the weakening of the gluten's ability to absorb water and deterioration of quality. The gluten quality of wheat that has gone through the post-ripening period is better than that of wheat that has not gone through the post-ripening stage. If the newly ground flour is not "fusang" processed, the gluten will be weak and loose, and the elasticity and extensibility will be poor.
The quantity and quality of gluten only consider the processing performance of noodles. As a food, the food texture must also be considered. From the perspective of food texture, it is better to choose soft wheat flour, but its moisture content is low. From the perspective of processing performance, it is better to choose hard wheat flour, but its food texture is poor. Therefore, hard wheat and soft wheat flour should be mixed in a certain proportion for instant noodles production.
my country’s flour standards only stipulate the content of wet gluten. Sometimes it is not enough to measure the content of wet gluten in actual operations, because the content of wet gluten has certain errors due to manual operation, so wet gluten is used as the There is an error in a standard value for a wheat characteristic. Therefore, while measuring the wet gluten content, the protein content should also be measured, and if possible, the quality of the gluten should also be measured. When producing fried instant noodles, the protein content in flour is recommended to be 11%.
3 The impact of flour processing quality on the production of instant noodles
3.1 The impact of wheat germ content
The increase in wheat germ content in flour can improve the yellow color of noodles Although wheat germ has little effect on flour, when alkali is added to the dough, the wheat germ will produce a yellow color due to the action of alkaline water. In addition, because wheat germ has high nutritional value, it plays a nutritional role in flour.
3.2 Effect of whiteness
The whiteness index of flour has a significant impact on the color and brightness of noodles. Flour containing too much bran starch will reduce the color of the noodles and make them dark. In order to obtain good quality noodles, the color grade of the flour needs to be controlled below 2.
3.3 Effect of the degree of starch granule damage
Damaged starch affects the water absorption rate of the dough (the water absorption rate is 3 times that of normal starch) and the extensibility of the dough. Therefore, the surface of the instant noodle product is sticky, the soup is mushy, and the palatability is poor. The gloss of cooked noodles depends on the degree of gel formation by starch, and the increase in damaged starch affects the activity of α-amylase and the degree of gluten gel, reducing the gloss of cooked noodles. When milling, the damaged starch in the flour should be controlled within the range of 120-170 mg (maltose value).
3.4 Effect of particle size
Fine and uniform flour particles can produce a uniform dough protein network structure and uniform color, and the final product can be made through dough mixing, aging, tableting and other processes. The color is relatively uniform.
4 Tensile curve of flour
After kneading, the dough has a certain strength, but it should not be too high, otherwise it will be difficult to press and cut into strips. Generally, the tensile curve is measured The value should be higher than 300BU units, but not higher than 600BU units.
5 The impact of ash content on the production of instant noodles
In wheat flour, the ash content is directly proportional to the starch content. High ash content means high starch content, and vice versa. High ash content not only affects the color and smell of flour, but also affects the uniform water absorption of wheat flour during mixing and affects the formation of gluten network. Therefore, the level of ash content directly affects the quality of noodles. Compared with similar foreign flours, the ash content standards of my country's wheat flour are on the high side. Reducing ash content can directly improve noodle quality. Japan’s dry noodle standards revised in 1985 clearly stipulated that the ash content of wheat flour, the raw material for noodle making, should be less than 0.5%. In reducing the ash content of flour in our country, there are problems such as increased costs, equipment, and technology, which need to be solved.
6 The impact of amylase and protease on instant noodle production
The higher the content of these two enzymes in flour, the more detrimental it is to noodle making. Because amylase breaks down starch, causing the viscosity of the dough to decrease, the content of soluble substances in the soup increases when the noodles are eaten. Protease can break down protein and affect the quality and quantity of gluten, resulting in reduced dough viscosity and poor taste when eaten. Apparently, amylase and protease also cause dough viscosity to decrease, but protease has a particularly great impact on noodle making.
This article comes from China Flour Information Network mf.net
The noodles are stiff and have poor taste; the viscosity is too small, the noodles have poor elasticity and are easy to rot, and are rough and poor in luster.
1. Protein has a greater impact on the quality of instant noodles than starch; both play almost equally important roles in influencing the quality of dried noodles. 2. Within a certain content range (9-12%), protein quality has a greater impact on the quality of dried noodles and instant noodles than its content. The sedimentation value has the greatest impact on the quality of noodles and instant noodles; the tensile parameters at 45 minutes have a greater reference value for the texture properties of noodles and instant noodles than the tensile parameters at 90 minutes and 135 minutes; the protein content and wet gluten content not only affect the bending resistance of dry noodles In addition to the significant impact on strength, it has little impact on other quality indicators of dried noodles and instant noodles; the gelatinization characteristics of flour or starch have a greater impact on the quality of dried noodles than instant noodles. 3． The impact of protein and starch on the quality of dried noodles and instant noodles is mainly reflected in their content and composition. Door) With the increase of protein content, the steaming time of noodles is extended, the water absorption rate during the cooking process of instant noodles decreases, and the breaking force and maximum deformation degree of instant noodles after cooking increase (the muscle strength increases); as the total starch content increases , the dry matter loss rate of instant noodles increases during cooking, the adhesiveness of instant noodles decreases after cooking, and the elasticity, fracture energy and maximum deformation degree (strength and toughness) of instant noodles after cooking decrease. Door) Gluten protein components have an important impact on dried noodles and instant noodles: gliadin has the greatest impact on the viscoelasticity (adhesion, chewiness, elasticity) of instant noodles, while glutenin plays a decisive role in the tensile properties of instant noodles. . Gliadin gives noodles elongation, and glutenin gives noodles resistance to elongation.
() The small A-type starch content has no significant impact on the quality of dried noodles and instant noodles; the increase in B-type starch content weakens the adhesion of boiled instant noodles, shortens the steaming time of noodles and the optimal cooking of dry noodles. Time; as the large A-type starch content increases, the rehydration time of instant noodles decreases, the oil content increases, the optimal cooking time of noodles shortens, and the maximum tensile strength of noodles after cooking decreases; gliadin The increase in gluten content increases the adhesion of boiled instant noodles and the tensile energy of boiled noodles; the increase in gluten content helps to increase the tensile energy of instant noodles and the breaking force of boiled noodles. (4) Starch (especially large A-type starch) is the primary factor affecting the compression properties of noodles, followed by glutenin; gliadin has the greatest impact on the tensile properties of noodles, followed by glutenin. (5) The amylose content is only significantly positively correlated with the elasticity of cooked noodles, but the correlation with other quality indicators does not reach a significant level. 4. The mechanism of protein's influence on the quality of dried noodles and instant noodles is that glutenin and gliadin give the dough formability by forming a gluten network structure; they produce agglomeration denaturation by heating, giving the noodles strength, hardness and partial elasticity. The impact of protein on the processing quality and eating quality of dried noodles and instant noodles is positive. 5. The mechanism of starch's influence on the quality of noodles and instant noodles is that starch gives plasticity to the dough through filling and dilution; it gives adhesion, softness and partial elasticity to noodles through gelatinization and aging. The impact of starch on the processing quality and eating quality of dried noodles and instant noodles is negative.