What is the gelatinization process of starch grains?

In order to complete the whole gelatinization process, starch must go through three stages: the reverse water absorption stage, the irreversible water absorption stage and the granule disintegration stage.

1) Reversible water absorption stage. Starch is at room temperature and does not change in any nature even when soaked in cold water. The starch present in cold water becomes a suspension after stirring, and if the stirring is stopped, the starch granules will slowly sink again.

In the process of cold water soaking, although the volume of starch granules expands slightly due to the absorption of a small amount of water, it does not affect the crystalline part in the granules, so the basic properties of starch do not change. At this stage, the water molecules entering the granules can be discharged with the re-drying of the starch, and the water molecules can be completely restored to the original state after drying, so this stage is called the reversible water absorption stage of starch.

2) Irreversible water absorption stage. When the starch and water are heated by heat, the water molecules begin to gradually enter the crystalline area in the starch granules, and the phenomenon of irreversible water absorption occurs. This is because as the temperature of the outside world increases, some of the chemical bonds within the starch molecule become very unstable, thus favoring the breaking of these bonds.

With the breaking of these chemical bonds, the crystalline area in the starch granules changes from the original tightly arranged state to a loose state, which makes the water absorption of starch increase rapidly. As a result, the volume of starch granules expands dramatically, and its volume can expand to 50,100 times its original volume. If the starch at this stage is re-dried, its water will not be completely discharged and will return to its original structure, so it is called the irreversible water absorption stage.

3) Particle disintegration stage. After the second stage of irreversible water absorption, the starch granules soon enter the third stage - the granule disintegration stage. Because, at this time, the ambient temperature of the starch continues to increase, so the starch granules continue to absorb water and expand.

When its volume expands to a certain limit, the granules will be ruptured, and the starch molecules in the granules will stretch and spread in all directions, dissolving out of the particles, and the expanded starch molecules will be connected and entangled with each other to form a network of hydrous colloids. This is the paste that appears after starch has been gelatinized.

Starch granules are generally insoluble in cold water, and gelatinization can occur when heated to a certain temperature in an aqueous system. Starch granules can be divided into three stages from water absorption and swelling to complete gelatinization: at the beginning of heating, the granules absorb a small amount of water, the volume expands less, the surface of the granules becomes soft and gradually sticky, but it does not dissolve, and the viscosity of the aqueous solution does not increase, and if it is dehydrated and dried at this time, it can still return to the granular state; In the second stage, as the temperature rises to a certain extent, the starch granules expand sharply, the viscosity increases greatly, and part of the amylose is dissolved in water, and the temperature at which this phenomenon occurs is called gelatinization temperature; In the final stage, as the temperature continues to rise, the starch granules increase to hundreds or even thousands of times, most of the starch granules gradually disappear, the viscosity of the system gradually increases, and finally becomes a transparent or translucent starch glue, at which time the starch is completely gelatinized.

The gelatinized starch molecular chain is relatively stretched, and there is sufficient free water and bound water in the system, which is soft and elastic.

Starch gelatinization refers to the degree of maturation of starch during processing, that is, the proportion of gelatinized starch to total starch amount. The gelatinization of feed starch basically occurs through the combined action of moisture, heat, mechanical energy, pressure, pH and other factors. Gelatinization plays an important role in digestion, it can improve the ability of starch to absorb water, so that enzymes can degrade starch, thereby improving the digestibility of starch.

Starch gelatinization. Starch is insoluble in cold water, but it absorbs water and swells. When heated, water molecules enter the inside of the starch grains, so that the starch grains continue to expand.

Its volume can increase several times to dozens of times, and the suspension immediately becomes a viscous colloidal solution, a phenomenon called "gelatinization of starch". The temperature at this time is called the gelatinization temperature, and the gelatinization temperature of wheat is.

The gelatinization temperature of starch grains is an important technical parameter in the production of baked goods. Generally, gelatinization is prevented before molding, but if it is not well controlled, it cannot be operated if it is too sticky during molding. When baking, it should be fully gelatinized to make the product mature, otherwise the eating quality will be poor.

When starch is mixed in cold water and stirred, it becomes an emulsion suspension, which is called starch syrup. If the stirring is stopped, after a certain period of time, all the starch grains will sink, and the upper part is water, because the starch is insoluble in cold water and its relative density.

For the sake of the larger water. The insoluble nature of starch granules in cold water is due to the direct formation of hydrogen bonds between hydroxyl groups or the indirect formation of hydrogen bonds through water. The hydrogen bonding force is weak, but the hydrogen bonding in the starch grains is sufficient to prevent the starch from falling in cold water.

There is a slight wetting of the starch in cold water (10%-15% increase in diameter), but this is reversible and the starch grains return to their original shape after drying.

If the starch milk is heated to a certain temperature, the water molecules.

enters the amorphous part of the starch grain, combines with a part of the starch molecule, breaks the hydrogen bonds and hydrates them; With the increase of temperature, the hydrogen bond in the crystalline area of the starch grain is broken, and the starch irreversibly and quickly becomes a very viscous starch paste, and the transparency is also increased. Even if the stirring is stopped, the starch will no longer settle. This viscous paste is called starch paste, and this phenomenon is called gelatinization, and the temperature required for this gelatinization to occur is the gelatinization temperature.

The essence of gelatinization is the breaking of hydrogen bonds between ordered (crystalline) and disordered (amorphous) starch molecules in starch, and the starch molecules disperse in water to form hydrophilicity.

Colloidal solution. As the temperature continues to increase, more starch molecules dissolve in the water, and the starch loses its original shape, and the microcrystalline bundle disintegrates accordingly, and finally only an outermost unformed empty sac remains. If the temperature continues to rise, all the starch grains will be dissolved, and the viscosity of the solution will drop significantly.

Therefore, in general, starch paste contains not only highly expanded starch grains, but also dissolved linear chain molecules, dispersed branched chain molecules, and some microcrystalline bundles.

The whole gelatinization process can be divided into three stages: reversible water absorption stage, water enters the amorphous part of the starch granules, the volume expands slightly, at this time it cools and dries, can be restored, and the birefringence phenomenon remains unchanged; In the irreversible water absorption stage, with the increase of temperature, water enters the starch microcrystalline gap, irreversibly absorbs a large amount of water, and the crystals "dissolve"; After starch gelatinization, continuous heating will make the expanded starch grains continue to separate and disintegrate, the starch granules will become amorphous bags, all the starch molecules will enter the solution, and the viscosity of the solution will continue to increase. The fresh gelatinized starch slurry is dehydrated and dried to obtain an amorphous powder that is easily dispersed in cold water, i.e., "soluble starch".

Questions. How to look at the gelatinization effect to understand that it has entered the third stage.

He is divided into 3 stages, and I have marked them all for us.

Gelatinization and overseeding generally refers to the gelatinization (-ization) of starch, which is to mix starch in water and heat, and after reaching a certain temperature, the starch grains swell and collapse to form a viscous and uniform transparent paste solution. The essence of starch gelatinization is that water enters the microcrystalline bundle and dissolves the association state between starch molecules, so that the starch molecules lose their original orientation arrangement.

"Aging"Yes"Gelatinization"The inverse process,"Aging"The essence of the process is that during the gelatinization process, the starch molecules that have been dissolved and expanded are rearranged and combined to form a substance similar to the natural starch structure. It is worth noting:

The process of starch aging is irreversible, and it is impossible to return to the pre-aging state through gelatinization.