Nitrogen Solubility Index (NSI) of okara was 38 which was only about half of soybean (71) Maximum protein recovery of 97 0% and 93 4% was achieved with soybean and okara flour from their respective fine fractions (<75 mu m) in a three-step-sequential extraction Recovery of protein from unclassified primary ground flour of soy and okara was much lower compared to their corresponding fine fractions (particle size <75 mu m) Secondary grinding of coarse fraction improved the overall protein recovery to an extent of 3 3% in okara and to a much larger extent of 6 8% in soybean Results showed that a two-step sequential extraction with respective solid-to solvent (w/v) ratios of 1 20 and 1 10 was suitable in terms of protein recovery Protein recovery from soy granules and okara flakes improved by 30 6% and 6 9% respectively with the introduction of primary and secondary grinding steps indicating the benefits of the proposed approach for practical applications (C) 2010 Elsevier Ltd All rights reserved