Soluble Dietary Fiber From Soybean Dregs By Fermentation

Soluble dietary fiber of soybean dregs is a kind of functional food additives. It can stabilize protein particles at low pH, has not only the physiological activity of dietary fiber, but also functiional characteristics of emulsion, antioxidative activities, anti-sticky, etc.. SDF of soybean dregs could be used as natural functional additives added to various food products, and the product has a good stability and healthy function. Accordingly, it has a great prospect to extract and develop product of soybean SDF!Trichoderma reesei Rut C-30 was mutagenesised with UV and cultured on medium of soybean dregs.The mutant strain secreted cellulase and hemicellulase to hydrolyse IDF of soybean dregs which can improve the conversion rate of SDF and the utilization of soybean dregs. Low extraction rate of soybean dregs SDF can be increased. The results showed that:1. The best medium of screening was cellulose media. Excellent mutant strains of cellulase can be screened out with high output quickly and accurately on the media. The optioal condition is 40s under UV with deadly rate of 80%, positive mutation rate of 31%.2. Mutant strains with high enzyme activity and output could be screened out by hydrolysis circle. According to the correlation analysis of hydrolytic circle, enzyme activity and SDF yield, enzyme activity and SDF were high as HC value increased. Mutant strains of high cellulase output had high enzyme activity of hemicellulase, too. The changes of SDF and enzyme activity had relationship.3. By optimizing different fementation conditions such as ratio of medium to water, pH, influence of fermentation on yield of SDF was studied. The optimal fermentation conditions were ratio of 1∶20 for soybean dregs and water, 4d age for Mutant strain, inoculation amount of 3%, at pH4.5 and 28℃, with rotate speed of 160r/min, incubation for 3d. After extraction, the SDF yield of soybean dregs was 42.79% at the most.4. The changes of soybean dregs components during fermentation were studied.The reason for SDF to increase in soybean dregs was mainly attributable to the transform of cellulose and hemicellulose. Cellulase and hemicellulase were important for degradation and transformation from IDF to SDF. The cellulose of soybean dregs was decomposed easier than hemicellulose. At the end of fermentation, cellulose and hemicellulose were decomposed by 90% and 55.4% respectively. SDF of soybean dregs was raised from 20% to about 40%, IDF of soybean dregs was decreased from 53 % to 20%.The transformation processing was not the same rate between IDF and SDF of soybean dregs.5. The optimal conditions for the extraction of SDF were studied. They were the solid-liquid ratio of 1∶40, at pH6.0 and 121℃with time of 60min, filtration and concentration. Anhyfrous ethanol(four times of filtrate volume)was added to the filtrate, precipitated for 60min. The SDF content of soybean dregs was 43.41%.6. SDF from soybean dregs by fermentation was preparated to accord with the quality of the country's grain industry standards. The particles of the SDF prepared by fermentation were smaller than ones extracted directly,and the particles were irregular in shape under the electron microscopy. The molecular weight of SDF was about 252356, 61152, 4993, 1011 by the gel exclusion chromatography. The result of IR analysis showed that the characteristics of SDF were typical infrared spectra of polysaccharide. There were the characteristic absorption peaks of functional groups of polysaccharide. SDF of soybean dregs were likely acidic polysaccharides or glucidamin, composition ofβ-D-glucose,β-D-galactose,α-D-xylose, D-deoxy-rhamnose.