Relationship between rehydration rate and gelatinization degree of instant rice

After the rice is extruded and puffed, under the action of high temperature, high pressure, shearing and many other factors, the starch is alphaized, which improves the solubility, reconstitution, digestibility and flavor of the starch molecule, and the protein is organized to make the Its dissolution rate is improved. Up to now, there is no report systematically discussing the detailed influence mechanism of each process parameter on the expansion ratio of the extrudate when extruding rice starch under high temperature shearing conditions. 

This paper aims to determine the best production process of extruded instant rice by studying the relationship between the puffing degree and the rehydration rate, gelatinization degree and other parameters, shorten the rehydration time, improve the product quality, and at the same time, it is the best way for the extrusion and puffing of the extruded rice. Establish relevant standards to solve the current lack of production standards in the domestic extruded artificial rice industry, promote the technological progress of the extruded artificial rice industry, and enhance the competitiveness and public service capabilities of the food extrusion industry.

2.1 The effect of moisture content on the radial expansion rate and rehydration rate of rice extrudates

In the extrusion process, the increase of water content is conducive to the swelling of starch and promotes the degree of gelatinization. In addition, water has a great influence on the viscosity of the melt, and acts as a plasticizer for biopolymers such as starch and protein. The flash evaporation of water when the material is extruded can promote the product to form a porous and loose structure, which is conducive to rehydration.

2.2 The effect of screw speed on the radial expansion rate and rehydration rate of rice extrudates

When the material passes through the extruder, the longer the residence time, the greater the degree of swelling of the starch granules; the greater the shearing effect in the machine, the easier it is to gelatinize. With the increase of the screw speed, the residence time of the material in the barrel is shortened, the time for the material to be affected is reduced, and the gelatinization degree of the material is reduced. On the other hand, the increase of the screw speed increases the corresponding shearing effect, and the shearing effect of the material can offset the negative effect caused by the relatively shortened residence time. Therefore, the effect of screw speed on the gelatinization degree of the material is a comprehensive effect.

2.3 The effect of temperature on the radial expansion rate and rehydration rate of rice extrudates

The expansion rate of cereal starch is mainly determined by the degree of gelatinization, which in turn is affected by factors such as temperature and moisture content. An increase in temperature leads to an increase in the degree of gelatinization and thus an increase in the expansion rate. However, when the barrel temperature exceeds a certain value, the starch molecules may be degraded, resulting in a decrease in the expansion rate. decrease in expansion rate.

3 Conclusions Expansion rate is an important index affecting the rehydration rate of instant rice. The barrel temperature has the greatest influence on the rehydration rate of the rice extrudate, followed by the moisture of the material and the feeding speed. The screw speed has the least influence on the expansion rate. Under different extrusion conditions, the radial expansion rate and the rehydration rate have the same change trend, and the rehydration rate and gelatinization degree also show the same change trend with the expansion rate.