Production of soy protein concentrates/isolates: traditional and membrane technologies

Production of soy protein concentrates (SPC)/isolates (SPI) by traditional acidic precipitation, ultrafiltration, electro-acidification and a novel approach combining electro-acidification and ultrafiltration is reviewed. In the context of the development of a combined electro-acidification ultrafiltration process, the impact of electroacidification on the filtration performance of soy protein extracts is investigated. The filtration performance is assessed for a two step process, diafiltration and concentration, using a flat sheet tangential flow system. Effect of feed concentration, membrane molecular weight cut-off and feed pH during filtration will be discussed.

Soy protein concentrates (SPC)/isolates (SPI) production by traditional acid precipitation, ultrafiltration, electro-acidification and a novel approach combining electro-acidification and ultrafiltration was reviewed. Emphasis was put on the combination of electro-acidification and ultrafiltration. Previous works with dead-end ultrafiltration [17,21] illustrated the feasibility and advantages of combining both technologies including the production of a concentrate (pH 6) with improved solubility characteristics, when compared to the use of ultrafiltration alone (pH 9), or a concentrate showing similar solubility profile to one produced by traditional acidic precipitation, but requiring two times less water during the process [17]. Low shear tangential flow ultrafiltration was used to evaluate the effect of electro-acidification on the fouling behaviour during the concentration of a diafiltered feed [22]. Electro-acidified extracts generally causes more fouling with a significant contribution associated with reversible fouling. This was attributed to the different properties of the extracts, more specifically to the charge of the proteins which is lower for the pH 6 SPE feed than for the pH 9 SPE feed, resulting in larger repulsive forces at pH 9 than at pH 6. Even though, the pH 6 SPE showed a higher global resistance, reversible resistance represents the main fraction of the global resistance. This observation suggests that filtration improvement i.e. fouling reduction can be achieved by operating in a high shear tangential mode such as with hollow fibre modules. It is expected that high shear will address the large reversible fouling contribution observed for the pH 6 SPE. Further work is needed to identify the feed constituents responsible for the irreversible fouling observed.