Amylose and amylopectin in dough Engineering
The main core elements of pastry and pastry engineering are protein and starch; pastry and baking engineering are actually protein and starch engineering; therefore, it is very important to understand wheat protein and starch; it is particularly important for the formula, technology and product quality of baked pastry food.
@Emulsifying and moistening
@Moisturizing and fresh keeping
Must start from understanding starch and protein - starch: soluble starch that can dissolve in hot water is called amylose; it can only expand in hot water, but can dissolve in cold water called amylopectin. The content of amylose is 20% - 25% in cereal starch, 30% - 35% in legume starch and 78% - 85% in waxy grain. The starch properties of all kinds of coarse cereals (corn, millet, sorghum, naked oats, beans, potato) are measured by molecular shape, degree of polymerization, end group, iodine reaction, amount of adsorbed iodine, coagulation property, coordination structure, X-ray diffraction analysis and acetyl derivatives; while the quality is measured by color, taste, impurities, water content, acidity, ash content, protein quality, spots, fineness Whiteness, fat, sulfur dioxide, lead, arsenic.
Both starch and protein in flour are hydrophilic, but the hydrophilicity varies with water temperature, thus forming water modified dough with different water temperature.
According to the test, under normal temperature, the properties of starch in flour are basically unchanged, and the water absorption rate is low. When the water temperature is 30 ℃, the starch can only combine about 30% of the moisture, and the granules do not expand, and can still keep the hard granule state; when the water temperature is about 50 ℃, the water absorption and expansion rate are still very low, and the viscosity changes little, but when the water temperature is above 53 ℃, the properties of starch will change obviously The higher the water temperature, the higher the degree of gelatinization, the greater the water absorption capacity, and the starch granule expansion * several times the original volume. That is, starch dissolves in water and produces viscosity. The higher the water temperature, the greater the viscosity.
When the starch is 30 ℃, it can combine 30% water; when it is 60 ℃, the swelling rate, gelatinization degree and water absorption rate will change step by step; when the temperature is high, the expansion volume of starch molecular particles is many times of the original volume, and the starch dissolves in water, the viscosity is greater (when it is hot, it is gelled when it is cold).
The mainstream framework of cake engineering is the skeleton structure of protein and starch; therefore, it is important to understand the outline of protein and starch; modern derivative baking technologies such as emulsification, fermentation, preservation, flavor enhancement, flavor enhancement and color enhancement are all based on the mainstream framework of protein and starch structure.
Starch is insoluble in water at room temperature, but its physical properties change obviously when the water temperature is above 53 ℃. Starch in high temperature swelling, splitting into a uniform paste solution characteristics, known as starch gelatinization.
Starch is divided into amylose and amylopectin. Amylose is soluble in water, viscous and easy to digest, while amylopectin is the opposite.
Amylose is a kind of chain compound composed of glucose and α - 1,4-glucoside bond. It can be hydrolyzed into maltose by amylase. It can be dissolved in hot water but not mushy. It turns blue with iodine. Stem rice and canmi contain more amylose.
Corn starch is generally amylose. The viscosity and adhesion of corn starch are weak. Therefore, corn starch is mostly used in pharmaceutical or dextrin glucose production. It can"t be used to make vermicelli, vermicelli, etc. But there are also exceptions, sticky corn (waxy corn) has more amylopectin. The amylopectin content of Waxy Corn Varieties with good quality can reach ****.
Amylopectin, also known as gelatinous starch, is relatively large and generally consists of thousands of glucose residues. Amylopectin is difficult to dissolve in water. Its molecules have many non reducing ends, but only one reducing end, so it does not show reducibility. Besides the α - 1,4-glycosidic bond, there are also α - 1,6-glycosidic bonds between glucose molecules in amylopectin. Therefore, with branches, about 20 glucose units have a branch, only the peripheral branched chain can be hydrolyzed to maltose by amylase. It is insoluble in cold water and swells into paste when it acts with hot water.
Glutinous rice is almost **** amylopectin, so cooked glutinous rice is sticky and not easy to digest.
The starch in rice mainly exists in amylopectin and amylose. The higher the amylopectin content is, the more elastic the rice is. Amylose is difficult to decompose and is not easy to be absorbed by human body, while amylopectin is easy to be decomposed and absorbed by human body.
Rice flour is mainly composed of amylopectin and amylose. Amylopectin is a polysaccharide carbohydrate whose viscosity is very high when it is preheated and fissured. Amylose has no viscosity. So we all know why glutinous rice has a high viscosity and why rice has no viscosity. Glutinous rice amylopectin 98%, amylose 2%; japonica rice amylopectin 83%, amylose 17%; indica rice amylopectin 70%, amylose 30%; rice amylopectin 30-40%, amylose 60-70% All rice products, such as mud cake, yellow cake, white sugar rice cake, tangtuan, etc.
In the application of puffed food, amylose and amylopectin have significantly different puffing effect due to different viscosity, swelling degree and moisture. Amylose has stronger tensile strength and good formability, which can increase the brittleness and strength of the product; amylopectin forms a network structure in it, which helps to increase the expansion volume and enhance the crispness of food. In order to obtain the expansion volume of * *, it is not the higher the amylopectin content is, the better it is, but a proper ratio of direct branch. The two components have mutual restriction and there is a * * ratio. In actual processing, different effects are often obtained by adjusting different direct branch ratio.
The modified starch can be divided into three types
① Acid treated starch: the starch obtained by partial hydrolysis of the original starch under the condition of being pulpy. Acid treated starch has low gelatinization pick-up viscosity, high aging, easy saponification, and no swelling property of other starch. After aging, it has strong firmness and high adhesive force.
② Baking dextrins: the starch obtained by baking the original starch at a specific high temperature, which has the characteristics of strong solubility in cold water and good rehydration.
③ Oxidized starch: the modified starch obtained by oxidizing the original starch, which has the characteristics of low viscosity, good stability and high transparency.
④ Starch ester: modified starch in which some or all hydroxyl groups in starch are aliphatic, soluble in cold water, stable viscosity at low temperature, and high transparency.
⑤ Starch ethers: modified starch with partial or all hydroxyl groups etherified in starch. It is stable to acid, alkali, temperature and oxidant. It can be hydrolyzed into dextrin and sugar by acid and heat, or oxidized into different products by hypochlorite, but the ether substituent remains unchanged.
⑥ Cross linked starch: it is a kind of modified starch with bifunctional or multi-functional groups to form cross-linked modified starch with high gelatinization temperature and stable paste viscosity.
⑦ Graft copolymerization starch: starch is grafted with acrylonitrile, acrylic acid, acrylamide, methyl methacrylate, butadiene, styrene and other synthetic polymer monomers to form graft copolymer. **It can be used as thickener, absorbent, sizing agent, adhesive and flocculant. The copolymer produced is insoluble in water and soluble in resin and plastic.
⑧ Physical modified starch: physical methods are used to make starch molecules produce active free radicals, and then the monomers of synthetic polymers are added. The temperature is 20-30 ℃ and there is no oxygen. The mechanism of starch aging is that the gelatinized a-starch becomes opaque and even coagulates and precipitates after being placed at or below room temperature. This phenomenon is called aging. This is due to the fact that the gelatinized starch molecules automatically arrange at low temperature, and the hydrogen bonds between adjacent molecules gradually recover to form dense and highly crystalline starch molecular microbubbles. Starch with water content less than 10% or in a large amount of water is not easy to aging, and it is easy to be aged when it is 30-60%; the most suitable temperature for aging is about 2-4 ° C, and it will not be aged when it is more than 60% or less than - 20 ° C; it is also not easy to be aged under acidic (pH < 4) or acid conditions. Knowing the cause of aging will reverse the introduction of bread and cake aging technology.