Structural characteristics and functional properties of rice bran dietary fiber modified by enzymatic and enzyme-micronization treatments

Using cellulase, xylanase, and ball-milling, the influences of enzyme and enzyme-micronization treatments on the structural and functional properties of rice bran dietary fiber (RBDF) were investigated. Due to the degradation of insoluble dietary fiber, the cellulase, xylanase, micronization, combined enzymes, and enzyme-micronization treatments increased the soluble dietary fiber content by 3.8, 4.7, 3.5, 10.0, and 11.4 fold, respectively. Scanning electron microscopy analysis indicated the enzymatic treatments caused the breakage of RBDF structure, and the enzyme-micronization treatment totally broke the RBDF matrix. Cellulase and xylanase increased RBDF crystallinity because of the hydrolysis of hemicellulose and the amorphous portion in cellulose, while enzyme-micronization reduced RBDF crystallinity due to the destruction of crystalline structure. Infrared spectroscopy indicated the breakage of intra-molecular hydrogen bonding and increased oligosaccharides, and differential scanning calorimetry analysis showed the oligosaccharides melting and reduced water-evaporating peaks because of the enzymatic and enzyme-micronization treatments. Additionally, enzyme and enzyme-micronization reduced the water and oil holding capacity, but increased the swelling capacity, cholesterol and sodium taurocholate absorption capacity of RBDF. The results suggest that cellulase and xylanase can modify the structural and functional attributes of RBDF, and the enzymatic treatments assisted with micronization is more effective in modifying the RBDF properties.