Starch, such as edible corn starch, can be hydrolyzed under dilute acid (such as dilute sulfuric acid) (requires heating) or enzymatic catalysis: (C6H10O5)n (starch) + nH2O → nC6H12O6 (glucose).

U7彩票U7CCPre-gelatinization

Pre-gelatinized starch is a kind of modified starch with simple processing and wide application. It can be used to adjust the paste with cold water to avoid the trouble of heating gelatinization. Widely used in many industries such as medicine, food, cosmetics, feed, oil drilling, metal casting, textile, papermaking, etc.

Gelatinization of starch: The effect of starch granules swelling, splitting, and forming a homogeneous paste-like solution in water at a suitable temperature (different temperatures of starch from various sources, generally 60-80 ° C) is called gelatinization. The essence of gelatinization is the hydrogen bond break between the ordered and disordered (crystalline and amorphous) starch molecules in the starch granules, which is dispersed in water to form a colloidal solution.

The process of gelatinization can be divided into three stages: (1) the stage of reversible water absorption, the moisture enters the amorphous part of the starch granules, and the volume expands slightly. At this time, the particles are cooled and dried, the particles can be restored, and the phenomenon of birefringence is unchanged; 2) Irreversible water absorption stage, as the temperature rises, water enters the gap of starch crystallites, irreversibly absorbs a large amount of water, and the phenomenon of birefringence gradually blurs and disappears. The crystal is also "dissolved", and the starch granules swell to 50 to 100 times the original volume. (3) The starch granules finally disintegrate, and the starch molecules all enter the solution.

U7彩票U7CCThe gelatinized starch is also known as alpha-starch. The freshly prepared gelatinized starch slurry is dehydrated and dried to obtain an amorphous powder which is easy to disperse and cool water, that is, "soluble α-starch".

2. Method for determining starch gelatinization: optical microscopy, electron microscopy, light propagation, viscosity measurement, measurement of swelling and solubility, analysis of enzymes, nuclear magnetic resonance, laser light scattering, and the like. Viscosity measurement, swelling and solubility determination are commonly used in the industry. Second, acid modified starch

U7彩票U7CCStarch toothpick

U7彩票U7CCStarch toothpick

U7彩票U7CCBelow the gelatinization temperature, a product which is treated with a mineral acid to change its properties is called an acid-modified starch.

U7彩票U7CCReaction mechanism: During the treatment of starch with acid, the acid acts on the glycosidic bond to hydrolyze the starch molecules, and the starch molecules become smaller. The starch granules are composed of amylose and amylopectin. The former has α-1,4 bonds, the latter has α-1,4 bonds, and a small amount of α-1,6 bonds. These two glycosidic bonds are acid hydrolyzed. There is a difference in difficulty. Due to the influence of the crystal structure of the starch granules, the amylose molecules are bonded to a crystalline structure via hydrogen bonding, acid infiltration is difficult, and the α-1,4 bond is not easily hydrolyzed by the acid. On the other hand, the α-1,4 bond and α-1,6 bond of the amylopectin molecule in the amorphous region of the particle are more easily infiltrated by the acid and hydrolyzed.

U7彩票U7CCProcess and principle: The acid-modified starch is usually prepared by using concentrated starch slurry, the solid content is about 36%~40%, heated to the gelatinization temperature (usually 40~60 °C), adding inorganic acid and stirring one. Hours or hours. When the required acidity or degree of conversion is achieved,

Oxidation

U7彩票U7CCMany reagents can oxidize starch, but the most commonly used in industrial production is alkaline hypochlorite. Starch oxidized with hypochlorite is referred to as "chlorinated starch" (although chlorine is not introduced into the starch molecule during processing).

The hypochlorite oxidation of the starch syrup is carried out in an alkaline sodium hypochlorite solution where the pH, temperature and concentration of hypochlorite, alkali and starch need to be controlled. Adjust the pH to 8~10 with about 3% sodium hydroxide solution, and add 5~10% hypochlorite solution of available chlorine for a specified time. The pH is controlled by adding a dilute sodium hydroxide solution, and the acidic substance formed in the reaction is neutralized. By varying the time, temperature, pH, starch variety, hypochlorite concentration and hypochlorite addition rate, a variety of different products can be produced. When the oxidation reaction reaches the desired level, the pH is lowered to 5 to 7, and the reaction is terminated by adding sodium hydrogen sulfite solution or sulfur dioxide gas to remove excess chlorine therein.

Classification of modified starch

There are more than 2,000 varieties and specifications of modified starch, and the classification of modified starch is generally carried out according to the treatment method.

U7彩票U7CC(1) Physical denaturation: pre-gelatinized (α-formed) starch, γ-ray, ultra-high-frequency radiation treated starch, mechanically ground starch, wet heat-treated starch, and the like.

U7彩票U7CC(2) Chemical denaturation: The obtained modified starch is treated with various chemical agents. There are two major categories: one is to reduce the molecular weight of starch, such as acid-stained starch, oxidized starch, baked dextrin, etc.; the other is to increase the molecular weight of starch, such as cross-linked starch, esterified starch, etherified starch, and Star starch and so on.

(3) Enzymatic denaturation (bio-modification): various enzymes treat starch. Such as α, β, γ-cyclodextrin, maltodextrin, amylose and the like.

(4) Composite denaturation: a modified starch obtained by using two or more treatment methods. Such as oxidized cross-linked starch, cross-linked esterified starch and the like. The modified starch obtained by compound denaturation has the respective advantages of two modified starches.

In addition, the modified starch can also be classified according to the production route, such as dry method (such as phosphate starch, acid starch, cationic starch, carboxymethyl starch, etc.), wet method, organic solvent method (such as the preparation of carboxyl starch generally using ethanol As solvent), extrusion method and drum drying method (such as natural starch or modified starch as raw material to produce pre-gelatinized starch).

The difference between starch and dextrin: Dextrin is made from starch. The difference between the two is the difference in molecular weight, just like the relationship between protein and peptide.

Cross-linking

U7彩票U7CCThe concept of cross-linked starch is that the alcoholic hydroxyl group of the starch forms a diether bond or a diester bond with the polyfunctional group of the cross-linking agent, so that two or more starch molecules are "bridged" together in a multidimensional network structure. The reaction is called a cross-linking reaction.

U7彩票U7CCCross-linking refers to bridging between molecules to form a chemical bond, which enhances the hydrogen bond between molecules. When the crosslinked starch is heated in water, the hydrogen bond can be weakened or even destroyed. However, due to the presence of chemical bridging, the starch particles will remain unchanged to varying degrees.

U7彩票U7CCThe most commonly used cross-linking agents in China are: sodium trimetaphosphate, sodium tripolyphosphate, formaldehyde, phosphorus oxychloride, and epichlorohydrin.

U7彩票U7CCAcid denatured powder

U7彩票U7CCAcid-modified starch refers to a type of modified starch obtained by treating natural starch with a mineral acid below the gelatinization temperature and changing its properties.

U7彩票U7CCThe acid-modified starch is usually prepared under the conditions of a starch emulsion concentration of 36% to 40%, a temperature lower than the gelatinization reaction temperature (35 to 60 ° C), and a reaction time of 0.5 to several hours. When the desired viscosity or degree of conversion is achieved, the product is neutralized, filtered, washed, and dried.

Effect of reaction conditions on the properties of acid-modified starch:

1. Temperature The reaction temperature is the main factor affecting the performance of acid-modified starch. When the temperature is between 40 and 55 °C, the viscosity changes to temperature, and the temperature has risen to 70 °C. Therefore, the reaction temperature is generally selected in the range of 40 to 55 °C.

2. Types and amounts of acids Acids act as catalysts and do not participate in the reaction. Different acid catalysis is different, hydrochloric acid is the strongest, sulfuric acid and nitric acid are similar, when the temperature is high, and the acid dosage is large, the nitrate modified starch is light yellow due to the side reaction, so it is rarely used in actual production. The catalytic action of the acid is related to the amount of the acid, and the amount of the acid is large, and the reaction is severe.

U7彩票U7CC3. Starch milk concentration The starch milk concentration should be controlled at about 40%.

Esterified starch

The esterified starch refers to a type of modified starch obtained by esterification of starch milk with an organic acid anhydride (acetic anhydride, succinic anhydride, etc.) under a certain temperature below the gelatinization temperature.