Abstract
Currently, the predominant process for soy protein concentrate (SPC) production is aqueous ethanol washing of hexane-extracted soy meal. However, the use of hexane is less desired, which explains the increased interest in cold pressing for oil removal. In this study, cold-pressed soy meal was used as the starting material, and a range of water/ethanol ratios was applied for the washing process to produce SPCs. Washing enriched the protein content for the SPCs, regardless of the solvent used. However, we conclude that washing with water (0% ethanol) or solvents with a high water/ethanol ratio (60% and above) can be more advantageous. Washing with a high water/ethanol ratio resulted in the highest yield, and SPCs with the highest protein solubility and water holding capacity. The water-only washed SPC showed the highest viscosity, and formed gels with the highest gel strength and hardness among all the SPCs at a similar protein concentration. The variations in the functionality among the SPCs were attributed to protein changes, although the effects of non-protein constituents such as sugar and oil might also be important. Overall, the aqueous ethanol washing process combined with cold-pressed soy meal created SPCs comparable to commercial SPC in terms of composition, but with varied functionalities that are relevant for novel soy-food developments.
Highlights
Soybean has been recognized as a powerhouse of nutrients, rich in protein and oil, as well as carbohydrates [1]
We found that the soy protein concentrate (SPC) washed with 40% and 60% water/ethanol ratios presented the highest degree of protein denaturation among all the SPCs (Table 2), which might have resulted in more exposure of hydrophobic groups, and relatively lower Nitrogen Solubility Index (NSI) values
The SPC gels (80% and 100% ethanol washed) presented the highest G′ values as well as the longest length of the linear viscoelastic (LVE) regimes among all the gels after heating, which could be related to a higher gel strength
Summary
Soybean has been recognized as a powerhouse of nutrients, rich in protein and oil, as well as carbohydrates [1]. Various protein-rich ingredients can be obtained from it, which have gained great popularity due to their high nutritional value and versatile functional properties [2]. Three forms of soy protein-rich ingredients are commercially available according to the protein content (N × 6.25), namely soy flour (50–65%), soy protein concentrate (SPC, 65–90%), and soy protein isolate (SPI, >90%) [3]. SPC was the last one to be developed; it nowadays provides a broader application range than soy flour, and is less expensive than SPI [4]. Different washing processes have been developed for the production of SPCs, which have included: water washing of heatdenatured soy meal, acid washing at the isoelectric pH, and aqueous ethanol washing [6]
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