Production of Okara and Soy Protein Concentrates Using Membrane Technology

Microfiltration (MF) membranes with pore sizes of 200 and 450 nm and ultrafiltration (UF) membranes with
molecular weight cut off of 50, 100, and 500 kDa were assessed for their ability to eliminate nonprotein substances from
okara protein extract in a laboratory cross-flow membrane system. Both MF and UF improved the protein content of
okara extract to a similar extent from approximately 68% to approximately 81% owing to the presence of protein in the
feed leading to the formation of dynamic layer controlling the performance rather than the actual pore size of membranes.
Although normalized flux in MF-450 (117 LMH/MPa) was close to UF-500 (118 LMH/MPa), the latter was selected
based on higher average flux (47 LMH) offering the advantage of reduced processing time. Membrane processing of
soy extract improved the protein content from 62% to 85% much closer to the target value. However, the final protein
content in okara (approximately 80%) did not reach the target value (90%) owing to the greater presence of soluble fibers
that were retained by the membrane. Solubility curve of membrane okara protein concentrate (MOPC) showed lower
solubility than soy protein concentrate and a commercial isolate in the entire pH range. However, water absorption and
fat-binding capacities ofMOPC were either superior or comparable while emulsifying properties were in accordance with
its solubility. The results of this study showed that okara protein concentrate (80%) could be produced using membrane
technology without loss of any true proteins, thus offering value addition to okara, hitherto underutilized.