Effects of Micronization on Morphology and Functional Attributes of Radio Frequency Stabilized Brown Millet and Millet Bran

Brown millet and millet bran are rich in nutrients. After stabilization treatment, they are easy to store and transport. However, it is difficult for them to be accepted as food ingredients by consumers due to their poor texture and taste. Micronization can alter chemical and functional properties of materials, potentially improving quality of brown millet and millet bran, as well as their taste. This study investigated the effects of micronization on morphology attributes (particle size distribution, microstructure and color), functional attributes (oil binding capacity, water binding capacity, water solubility index, swelling capacity and bulk density), and digestion and release of free polyphenols and flavonoids in fresh and radio frequency (RF) stabilized brown millet and millet bran. The results showed that micronization treatment effectively reduced particle size of the samples, increased particle surface area, significantly improved powder color, and affected their microstructure. Micronization treatment also increased bulk density of brown millet and millet bran. When the particle size was reduced to pass through a 150-mesh sieve, the bulk density of fresh and RF stabilized brown millet and millet bran increased by 13.68%, 38.77% and 22.50%, 25.33%, respectively. Micronization reduced oil binding capacity and water binding capacity of the samples, and both indicators continuously decreased with the decline of particle size. Micronization also improved the release of antioxidant substances (free polyphenols and free flavonoids) from brown millet and millet bran. When digestion for 120 min, the release of free flavonoids in intestine of 150-mesh fresh brown millet powder increased by 70.89% compared with 50-mesh powder, and the release of free polyphenols in stomach increased by 12.22%. This study indicates that micronization can improve functional and nutritional attributes of brown millet and millet bran, offering valuable reference and guidance for the development of micronized raw materials from brown millet and millet bran.