Production of Okara and Soy Protein Concentrates Using Membrane Technology

Abstract

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 of MOPC 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. Practical Application: Okara, a byproduct obtained during processing soybean for soymilk, is either underutilized or unutilized in spite of the fact that its protein quality is as good as that of soy milk and tofu. Membrane-processed protein products have been shown to possess superior functional properties compared to conventionally produced protein products. However, the potential of membrane technology has not been exploited for the recovery of okara protein. Our study showed that protein content of okara extract could be improved from approximately 68% to approximately 81% without losing any true proteins in the process.

Optimization of air jet impingement drying of okara using response surface methodology

“…TIA could still be significant in the okara from soymilk production (Vishwanathan, Govindaraju, Singh, & Subramanian, 2011).…”

Valorisation of By-Products from Soybean (Glycine max (L.) Merr.) Processing

“…Regarding the protein fraction of okara, past research has focused on methods of extraction and modification that can make it suitable as an ingredient [36,37,40], while recent literature has reported detailed characterisation and composition [39,95]. In addition, Vishwanathan et al have investigated the extractability of proteins in SCR and the production of a protein concentrate by membrane separation [96]. A study on peptide preparation via protease hydrolysis has reported that the obtained products showed antioxidant activity [97].…”

“…Studies have also been conducted on the fractionation of specific components of okara, such as dietary fibres, proteins and isoflavones [96,[192][193][194][195][196]. This contributes both to the biovalorisation of these isolated components and to higher efficiency and yield than the direct fermentation of okara.…”

Filtration Behavior during Soymilk Separation Process

“…To date, there have been many investigations that have attempted to understand filtration mechanisms in the field of microfiltration (Grace, 1956;Granger et al, 1985;Hurt and Barbano, 2010;Tung et al, 2010;Vishwanathan et al, 2011). The filtration behavior in a membrane could be analyzed using a blocking model based on mathematical expressions (Hermans and Bredée, 1936).…”