The physical properties of dietary fiber are related to its chemical structure and its complex network structure, which includes amorphous and crystalline regions, hydrophilic and hydrophobic areas. The maintenance of the network structure relies on different strengths of chemical bonds and physical interactions. Therefore, the modification of dietary fiber has gained widespread attention.

Currently, the main methods of modifying soy dietary fiber include chemical, biological, ultrafine grinding, extrusion cooking, instant high-pressure treatment, and ultra-high-pressure food processing technology.

Chemical modification of soy dietary fiber

The concentration and strength of acid and alkali as well as the amount of water are advantageous to the conversion of soluble fiber (SDF) in soy dietary fiber. The change mainly takes place in the hemicellulose part, while the cellulose is minimally affected.

Ultrafine grinding of soy dietary fiber

The powerful shear, friction, and compression forces generated between the moving and fixed blades with fine gaps and high-speed rotation can cause strong damage to the material. The fiber can stretch and expand when immersed in wet state, with a relatively loose and brittle structure, and is more prone to fracture than in the dry state, which is conducive to obtaining ultrafine particles by using wet swelling and drying contraction.

The presence of water during grinding not only facilitates material transportation and improves feedability, but also cools the system and avoids material overheating. The ultrafine grinding high-intensity force can not only destroy the structure of non-water-soluble dietary fiber microparticles and cut off their connections, but also affect the crystalline state of the microparticles, forming a crystal loose zone and intercrystalline cracks, strengthening the crushing effect, reducing roughness and improving the palatability of dietary fiber.

Liquid-phase ultrafine grinding technology of soy dietary fiber

The ultrafine processing of the material particles of dietary fiber is mainly carried out by using a micro-jet homogenizer. However, due to the super-strong self-adsorption between ultrafine particles, aggregation is unavoidable, and the material system after being crushed by the micro-jet homogenizer exhibits an increase in viscosity, absorption, and turbidity, a decrease in transmission ratio, a small change in refractive index, and a decrease in total solids content.

Based on the working mechanism of the micro-jet homogenizer, some researchers have proposed the instant high-pressure treatment method, which means the instantaneousness of pressure change and processing. When the material passes through the core component reaction chamber of the micro-jet homogenizer rapidly under high pressure, it withstands a pressure of up to 300MPa in the reaction chamber. Due to the rapid passage of the material through the reaction chamber, the high pressure has a very short action time on the material, and the pressure change rate is extremely high. The material is subjected to mechanical forces such as high-speed collision, high-frequency oscillation (movement), instantaneous pressure drop, high-speed cutting, and cavitation when passing through the treatment chamber, which enables the material to obtain ultrafine grinding and further affect its physicochemical properties. Therefore, this process is collectively referred to as the instant high-pressure treatment process.

Ultra-high-pressure food processing technology refers to the treatment of food in a liquid medium under a pressure of 100-1000 MPa. The ultra-high pressure treatment process is a purely physical process, in which the volume of the material in the liquid medium is compressed. The extremely high static pressure generated by ultra-high pressure not only affects the shape of cells, but also changes the non-covalent bonds such as hydrogen bonds, ionic bonds, and hydrophobic bonds of the formed biological polymers' three-dimensional structures, causing protein coagulation and starch denaturation.

In summary, dietary fiber is of great significance to human health. People should increase the intake of dietary fiber in their daily lives, pay attention to the intake of grains, soys, vegetables, and fruits, which has very profound significance for preventing obesity, colon cancer, and cardiovascular and cerebrovascular diseases. Therefore, soy dietary fiber in the international market has great development potential.

Researchers actively use soy dregs and other research substrates rich in soy dietary fiber, continuously optimize the extraction process, in order to improve the efficiency of extracting soluble soy dietary fiber. This can not only solve the environmental problems and commercial problems caused by the substrates such as soy dregs, but also promote the development of related industries, promote the research and development of dietary fiber-based health foods, and have good prospects for development and application.