Pre-gelatinized

Pre-gelatinized starch is a kind of modified starch which is simple to process and has a wide range of uses, and it can be applied as long as it is adjusted into a paste with cold water, which exempts the trouble of heating and gelatinization. It is widely used in many industries such as medicine, food, cosmetics, feed, oil drilling, metal casting, textile and paper making.

Starch paste: starch granules in the appropriate temperature (various sources of starch at different temperatures, generally 60 ~ 80 ℃) in the water swelling, splitting, the formation of a uniform paste solution is called the role of paste. The essence of pasting is that the starch granules in the ordered and disordered (crystalline and amorphous) state of the starch molecules between the hydrogen bonding is broken, dispersed in the water to become a colloidal solution.

The process of pasting can be divided into three stages: (1) reversible water absorption stage, the water into the amorphous part of the starch grain, the volume of a slight expansion, at this time the cooling and drying, the particles can be restored, birefringence phenomenon remains unchanged; (2) irreversible water absorption stage, with the increase in temperature, water into the starch microcrystalline interstitial space, irreversibly a large number of water absorption, the phenomenon of birefringence gradually blurred to the disappearance of the crystals is also known as "dissolution" of the crystals. Crystallization "dissolution", starch granules swell to 50~100 times of the original volume; (3) starch granules finally disintegrate, starch molecules all into solution.

The pasteurized starch is also known as α-starch. Freshly prepared paste starch slurry dehydration and drying, can be easily dispersed with cool water amorphous powder, that is, "soluble alpha-starch".

2. Determination of starch pasting: optical microscopy, electron microscopy, light propagation, viscosity, swelling and solubility determination, enzyme analysis, nuclear magnetic **** vibration, laser light scattering method. Industry commonly used viscometry, swelling and solubility determination. Second, acid modified starch

Starch toothpick

Below the pasting temperature, with inorganic acid treatment of starch, change the nature of the product is called acid modified starch.

Reaction mechanism: In the process of treating starch with acid, the acid acts on the glycosidic bond to hydrolyze the starch molecules, and the starch molecules become smaller. Starch granules are composed of straight chain starch and branched chain starch, the former has α-1,4 bond, the latter in addition to α-1,4 bond, there are a small amount of α-1,6 bond, the two glycosidic bonds by the acid hydrolysis of the difficulty of the difference. Due to the crystalline structure of starch granules, straight-chain starch molecules are combined into a crystalline structure by hydrogen bonding, and it is difficult for acid to penetrate into it, and its α-1,4 bond is not easy to be hydrolyzed by acid. On the other hand, the α-1,4 and α-1,6 bonds of the branched starch molecules in the amorphous region of the granule are easier to be penetrated by acid and hydrolyzed.

Process and principle: Usually, acid modified starch is produced by using concentrated starch slurry with about 36%~40% solids, heated to below the pasting temperature (often 40~60℃), adding inorganic acid and stirring for one hour or several hours. When the required acidity or degree of conversion is reached,

Oxidation

Many reagents oxidize starch, but alkaline hypochlorite is the most commonly used in industrial production. Starch oxidized with hypochlorite is called "chlorinated starch" (although no chlorine is introduced into the starch molecules during the process).

The hypochlorite oxidation of starch emulsions is carried out in an alkaline sodium hypochlorite solution, where the pH, temperature, and concentrations of hypochlorite, alkali, and starch are controlled. The pH is adjusted to 8~10 with about 3% sodium hydroxide solution and hypochlorite solution with 5~10% effective chlorine is added for a specified time. The addition of a dilute solution of sodium hydroxide was used to control the pH and to neutralize the acids produced in the reaction. Varying the time, temperature, pH, starch variety, hypochlorite concentration and hypochlorite addition rate can produce a wide range of different products. When the oxidation reaction reaches the required level, the pH is lowered to 5~7 and the reaction is terminated by adding sodium bisulfite solution or sulfur dioxide gas to remove excess chlorine from it.

Classification of modified starch

There are more than two thousand varieties and specifications of modified starch, and the classification of modified starch is generally based on the treatment.

(1) Physical denaturation: pre-gelatinized (α-chemical) starch, γ-ray, ultra-high-frequency radiation-treated starch, mechanically milled-treated starch, and moist-heat-treated starch.

(2)Chemical denaturation: denatured starch obtained by treatment with various chemical reagents. There are two main categories: one is to make the molecular weight of starch decrease, such as acid digestion starch, oxidized starch, baking dextrin, etc.; the other is to make the molecular weight of starch increase, such as crosslinked starch, esterified starch, etherified starch, grafted starch, etc..

(3) Enzymatic denaturation (biomodification): various enzyme treatment of starch. Such as α, β, γ-cyclodextrin, maltodextrin, straight chain starch.

(4)Compound denaturation: denatured starch obtained by using more than two treatments. Such as oxidized crosslinked starch, crosslinked esterified starch and so on. The modified starch obtained by compound denaturation has the respective advantages of the two modified starches.

In addition, modified starch can also be classified according to the production process route, there are dry (such as phosphate starch, acid starch, cationic starch, carboxymethyl starch, etc.), wet, organic solvent method (such as carboxy starch preparation is generally used as a solvent for ethanol), extrusion and drum drying method (such as natural starch or modified starch as raw materials for the production of pre-pasteurized starch).

The difference between starch and dextrin: dextrin is manufactured from starch, the difference between the two is that the molecular weight is different, like the relationship between proteins and peptides.

Crosslinking

The concept of crosslinking starch is that the alcohol hydroxyl group of starch and the multifunctional group of the crosslinking agent form a diethyl ether bond or a diester bond, so that the two or more starch molecules are "bridged" together in a multidimensional network structure reaction, known as the crosslinking reaction.

Crosslinking refers to the formation of chemical bonds between the molecules of the bridge, strengthening the role of hydrogen bonding between the molecules. When cross-linked starch is heated in water, the hydrogen bonds can be weakened or even destroyed, however, due to the presence of chemical bridging, the starch granules will remain unchanged to varying degrees.

The most commonly used cross-linking agents in China are: sodium trimetaphosphate, sodium tripolyphosphate, formaldehyde, trichlorophosphorus, epichlorohydrin.

Acid modified powder

Acid modified starch cited as a class of modified starch obtained by treating natural starch with inorganic acid below the pasting temperature to change its properties.

The conditions for the preparation of acid modified starch are as follows: the concentration of starch milk is 36% to 40%, the temperature is lower than the pasting reaction temperature (35-60℃), and the reaction time is from 0.5h to several hours. When the desired viscosity or degree of conversion, neutralization, filtration, washing and drying of the product.

The effect of reaction conditions on the performance of acid modified starch:

1. Temperature The reaction temperature is the main factor affecting the performance of acid modified starch, when the temperature is 40 ~ 55 ℃, the viscosity change tends to temperature, the temperature rises to 70 ℃ has been paste. Therefore, the reaction temperature is generally selected in the range of 40 ~ 55 ℃.

2. Type and amount of acid acid as a catalyst without participating in the reaction. Different acids have different catalytic effects, hydrochloric acid is the strongest, sulfuric acid and nitric acid is similar, when the temperature is higher, the amount of acid is larger, nitric acid modified starch due to side reactions and make the product light yellow, so the actual production is rarely used. The catalytic effect of acid is related to the amount of acid, acid dosage is large, the reaction is violent.

3. Starch milk concentration Starch milk concentration should be controlled at about 40%.

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