Influence of particle size on protein extractability from soybean and okara

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 lm) 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 lm). 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.