Research Progress of Soy Dietary Fiber Extraction Process

Currently, both domestic and international companies are actively utilizing modern high-tech methods such as extrusion molding, membrane separation, fermentation engineering, enzyme catalysis, bioprocessing, modern food separation, high-pressure processing, microencapsulation, and advanced sterilization to improve the value of soy products. This not only vastly expands the range of soy deep processing applications and enhances overall development capabilities, but also maintains soy's nutritional ingredients during processing. In terms of extracting soy dietary fiber, there are many methods, including chemical, enzymatic, microbial fermentation, microwave-assisted extraction, and multiple methods combined.

Chemical extraction method for soy dietary fiber

Chemical extraction primarily refers to a combination of acid hydrolysis and alkali hydrolysis. Depending on the raw materials used, different concentrations and durations of acid and alkali hydrolysis yield different percentages of soy dietary fiber. Orthogonal experimental design is necessary to determine the optimal extraction process.

Enzymatic extraction method for soy dietary fiber

Enzymatic extraction's key technology relies on enzymatic reactions. Compared to chemical extraction, enzymatic extraction yields the highest percentage of soy dietary fiber for several reasons:

• Enzymes have high catalytic rates, exhibit strong specificity, and do not cause side reactions, thus resulting in high yield and quality and simplifying product purification and processing steps.

• The enzymatic reaction conditions are mild, and high temperature and pressure are not necessary, making the equipment requirements less demanding while saving energy such as coal and electricity.

• Enzymes and their reactants are mostly non-toxic and suitable for industrial production. However, in enzymatic extraction, soy pulp may have a strong odor and dark color, requiring pretreatment.

Note that in the enzymatic extraction of soy dietary fiber, the extraction temperature, solid-liquid ratio, and extraction time are the three most important factors affecting water-soluble soy dietary fiber extraction rates. The extraction temperature is the primary factor, followed by time, and then solid-liquid ratio.

Microbial fermentation method for extracting soy dietary fiber

Soy dietary fiber produced by microbial fermentation exhibits significantly enhanced physiological activity and is a high-quality dietary fiber. The production process is simple, low-cost, and has already achieved industrialization.

Multi-method combined extraction process for soy dietary fiber

The acid hydrolysis and alkali hydrolysis of chemical extraction must break the glycosidic bonds at appropriate pH, temperature, and time intervals to decrease the degree of polymerization, and the dietary fiber completes the transition from IDF to SDF. Even in mildly alkaline solutions, cellulose and hemicellulose undergo exfoliation, which is a peeling reaction where each sugar with a reducing terminal end drops off one by one until stable reactions occur, resulting in the transformation of the terminal group to uronic acid. The dropped off sugar ultimately becomes isomeric uronic acid and exists in the solution as its sodium salt.

Although both acid and enzymatic extractions decrease the degree of polymerization ofdietary fiber, the increased number of sodium isomeric uronic acid salt crystals limits the conversion of IDF to SDF in the alkaline breakdown procedure, resulting in a lower yield than acid breakdown for SDF. In contrast, enzymatic extraction has a high catalytic rate, which does not cause side reactions and operates at mild reaction conditions, making the equipment requirements simple and saving energy such as coal and electricity. However, due to the strong specificity of the reaction, enzymatic extraction requires higher-quality substrates and has varying yield rates. Therefore, multiple methods must be combined and their advantages and shortcomings utilized to maximize the extraction efficiency of soy dietary fiber.