Micronization Effects on Structural, Functional, and Antioxidant Properties of Wheat Bran

To explore the effect of micronization on the structural, functional, and antioxidant properties of wheat bran, wheat bran with mean particle size (D₅₀) of 46.08, 34.29, 26.51, 26.35, and 26.05 μm were prepared by using an ultrafine pulverizer under different rolling frequencies (0, 6, 9, 12, and 15 times). The main chemical components and structural, functional, and antioxidant properties of the wheat bran were compared and a correlation analysis was conducted. As the D₅₀ of the wheat bran decreased from 46.08 μm to 26.05 μm, the micromorphology exhibited the destruction of the bundle structure, which is formed by starch and fiber, during which the starch particles peeled off, the fiber fragments destructed, and some of the slim fiber fragments attached to the surfaces of the starch granules. According to the X-ray diffraction pattern, part of the crystalline structure was transformed into an amorphous structure and the crystallization index decreased from 13.08% to 3.95%. According to the near-infrared spectrum, more active groups, such as the hydroxyl group, were exposed; however, no new groups were generated. These structural changes accordingly caused changes in the chemical components, functional properties, and antioxidant properties of the wheat bran. Specifically, the protein, total phenols, total flavonoids, and fatty acid content increased by 6.72%, 23.47%, 19.07%, and 172.88%, respectively. The lipase activity, antioxidant activity in vitro (DPPH• scavenging activity, ABTS⁺• scavenging activity, and ferric reducing antioxidant power), and the water-holding, cholesterol-adsorption, sodium nitrite-adsorption, and cation-exchange capacities, were enhanced to some extent. The oil-holding capacity decreased from 3.01 g/g to 1.32 g/g. The swelling capacity decreased first and then increased and the swelling capacity of the wheat bran with a D₅₀ of 34.29 μm was the lowest (3.62 mL/g). Therefore, the micronization could be used as a pretreatment method to improve the functional and antioxidant properties of wheat bran; however, the optimal particle size of wheat bran is based on the function of the product.