Abstract: In this study, fresh okara was dried and subjected to ultrafine comminution alone or screw extrusion followed by ultrafine comminution. We established the optimum conditions for drying fresh okara and explored the effects of ultrafine comminution alone and in conjunction with screw extrusion on the particle size distribution and processing properties of okara powder. Ultrafine okara powder had better particle size distribution and processing properties than ordinary okara powder. The average particle sizes (D50) of ultrafine powder samples obtained after comminution for 10, 20, 30, 60 min were less than 10 μm and the 20-min ultrafine powder sample showed the best dispersibility, a water solubility of 21.34% and enhanced water-holding capacity and expansibility and yielded 4.5 g of filtration residue, suggesting that the optimum comminution time was 20 min. The combined use of screw extrusion and ultrafine comminution, although causing the color of okara to darken, could notably increase the dispersibility of okara powder in comparison with ultrafine comminution alone, and only 1.53 g of filtration residue was obtained from the resulting power, thereby being more suitable for the production of instant food products.

Key words: okara, ultrafine comminution, screw extrusion, processing properties