Analysis of protein enrichment during single- and multi-stage tribo-electrostatic bioseparation processes for dry fractionation of legume flour

The potential of a dry fractionation approach for the production of native plant protein concentrates has been validated for navy bean (Phaseolus vulgaris) flour as a model system utilizing a lab-scale tribo-electrostatic separator. For this approach, protein and carbohydrate particles in pin-milled flour were tribo-charged to different levels before being fractionated according to their acquired charge under the influence of an applied electric field. In the present study, the location and distribution of the charged protein-rich particles along the surface of the electrode plate was investigated as a function of air flow rate (laminar vs. turbulent) and electric field strength. A turbulent air flow rate at a variety of electric field strengths resulted in the formation of protein-rich particles and starch granule agglomerates affecting the production of high-purity protein concentrates. Charging the flour particles at a laminar air flow rate followed by separation under a low electric field strength enabled the production of fine protein-rich fractions with considerably higher protein contents (38.4–46.5%) but lower protein separation efficiency. The combination of a laminar air flow rate and high electrode voltage slightly reduced the protein content of the fraction (39.4–42.9%), but significantly improved the protein separation efficiency to ∼45%. To further improve the separation efficiency of the navy bean protein concentrate without compromising its protein content, a two-stage tribo-electrostatic separation approach was evaluated at a laminar air flow but different plate voltages. The combined protein-rich fraction produced by the two-stage approach had a protein content of ∼38% accounting for 60% of the total protein that was significantly higher than that of the optimized single-stage tribo-electrostatic separation, facilitating the scale-up of this dry fractionation technique for pilot-plant applications.