Extraction, Purification, and Characterization of Insoluble Dietary Fiber from Oat Bran

The dietary fiber in oats is mainly concentrated in the bran; however, the oat bran is mostly used for livestock and poultry feed and thus has a low utilization rate and low added value. In this study, insoluble dietary fiber (IDF) was extracted by a combination of α-amylase and neutral protease. The optimal extraction conditions of the IDF were obtained by response surface methodology. The material-to-water ratio was 1:12.1, the concentration of α-amylase was 1.85%, and the hydrolysis time was 39.14 min. After purifying the crude fiber with 4% sodium oxide (NaOH), 70 °C hot water, and anhydrous ethanol, the purity of dietary fiber exceeded 95%. X-ray diffraction analysis indicated that the IDF was predominantly amorphous. Scanning electron microscopy showed that the IDF surface exhibited a loose porous network structure. Fourier-transform infrared spectroscopy of the crude IDF showed characteristic absorption peaks at 3626, 2929, 1667, 1538, 1455, 1242, and 1048 cm−1, while the infrared spectrum of the purified IDF showed characteristic absorption peaks at 3401, 2924, 1744, 1643, 1418, and 1040 cm−1, which is consistent with the structure of cellulose polysaccharide. Differential scanning calorimetry analysis showed that there were three exothermic peaks at 270–310 °C, 320–350 °C, and 440–460 °C, which may represent the pyrolysis peaks of hemicellulose, cellulose, and lignin, respectively, indicating that the oat bran IDF had good thermal stability. The results indicate that the oat bran IDF can be used for the production of dietary fiber products and health-care products.