Effect of electro-acidification treatment and ionic environment on soy protein extract particle size distribution and ultrafiltration permeate flux

The present study emerges from the development of a process aimed at integrating electro-acidification and ultrafiltration for the production of soy protein isolate. It was observed that electro-acidification treatments, which change the pH and the salt content of the soy protein extracts, influence the permeate flux during dead-end ultrafiltration. The effects of electro-acidification treatments on the soy protein extracts were quantified through experimental measurement of particle size distribution, molecular weight profiles, protein solubility and particle volume fraction. A criterion for the particle deposition into the concentrated layer or at the membrane surface was obtained from the analysis of the net force along the direction of permeation. The particle size distribution and the criterion for the particle deposition were used to obtain information about the particle transport into the concentrated layer, as a function of the pH and salt content, and were related to the global resistance, which is mainly attributable to both concentrated layer and cake layer together. For soy protein extracts reconstituted in double distilled water or in 0.12 M KCl, it was found that particle size distribution vary with pH and salt content and this was mainly attributable to the aggregation-disaggregation behavior of the different proteins fraction. For the soy protein extracts reconstituted in double distilled water, the mean particle size, the particle transport into the concentrated layer and the global resistance were maximum at pH 7, slightly lower at pH 6 and minimum at pH 9. This resulted in minimum permeate flux at pH 7, slightly higher at pH 6 and maximum at pH 9. For the soy protein extracts reconstituted in 0.12 M KCl, all three parameters increased with a decrease of pH. This resulted in a permeate flux decrease with a decrease of pH. Crown Copyright (C) 2003 Published by Elsevier B.V. All rights reserved.