Structural characteristics and physicochemical properties of okara (soybean residue) insoluble dietary fiber modified by high-energy wet media milling

- Okara insoluble dietary fiber (IDF) was downsized to nanometer range by wet milling.
- Molecular and crystalline structure of IDF was disrupted after milling.
- Particle size reduction of the IDF contributed to modify physicochemical properties.
- Modified okara IDF may be applied as functional ingredient in foods.

Changes in structural characteristics and physicochemical properties of okara insoluble dietary fiber (IDF) during high-energy wet media milling process were analyzed. Particle size of the IDF was effectively reduced from 66.7 μm to 544.3 nm after 6 h of milling and kept constant (p > 0.05) as the milling process prolonged. As the particle size decreased, lightness and whiteness of the IDF significantly (p < 0.05) increased, zeta potential decreased continuously (p < 0.05). Swelling power, water solubility index and apparent viscosity extensively increased (p < 0.05) after 1 h of milling and then steadily decreased (p < 0.05). Electron microscopy observations showed that the IDF was changed from regular and compact rods to aggregates with puffed morphology. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis revealed that intermolecular hydrogen bonds and crystalline structure of the IDF polysaccharides were disturbed after milling.

205