Characteristics of Wheat Bran Classified by Ultra-Fine Grinding and Air-Classification Systems

Abstract

Using an air-classification system equipped with both ultra-fine grinding and air-classification, wheat bran was ground at a mill grinding speed of 3,800, 4,800, 5,800 rpm and a separator reverse wheel speed of 2,500, 3,000 and 3,500 rpm. Ground bran was air-classified with a reverse wheel speed of 200, 400 and 600 rpm. The effects of mill grinding, separation, and classification wheel speeds on the characteristics of air-classified bran were examined by a threelevel, three-factor full factorial experimental design and a response surface regression analysis. The highest value of the object variables was determined via canonical analysis. For the fraction ratio of classified bran products, both the fine and coarse fraction of brans were significantly affected by the mill grinding speed (p0.01), separator reverse wheel speed (p0.01), and air-classification reverse wheel speed (p0.01). For average particle sizes of classified bran products, the fine fractions were significantly affected by only the air-classification reverse wheel speed (p0.01), whereas the coarse fractions were affected by the mill grinding speed (p0.01) and the separator reverse wheel speed (p0.01). With regards to the total dietary fiber of classified bran products, the fine fraction products were affected by the mill grinding wheel speed (p0.01) and the air-classification reverse wheel speed (p0.01), while the coarse fraction products were affected by the mill grinding speed (p0.01), separator reverse wheel speed (p0.01) and the air-classification reverse wheel speed (p0.01). The optimal conditions for the highest total dietary fiber content, lowest average particle size and highest classification ratio in wheat bran were a 5,500.3 rpm mill grinding speed, 2,500 rpm separator reverse wheel speed and a 600 rpm air-classification reverse wheel speed, in which the total dietary fiber content was estimated to be 39.52 g/100 g in coarse fraction.