Separation behavior of yellow pea flour through a combined milling and tribo-electrostatic separation approach

Abstract: This study combined milling and tribo-electrostatic separation (TES) processes to assess the protein enrichment from yellow pea flour in a sustainable, non-destructive way. Before the TES process, the flour was milled using the pin and Ferkar milling systems equipped with 0.14- and 0.5-mm screen sizes. The samples were then tribo-charged under 7 to 14 LPM airflow rates and fractionated by being exposed to two parallel charged plates holding electric field strengths of ±3 to ±12 kV. The flours collected from the positively charged plate (PCP) and chamber bottom (CB) were protein-depleted, whereas the negatively charged plate (NCP) mainly attracted protein particles. In this study, we have assessed the effect of milling types and intensity, along with airflow rate and plate voltages, on TES fractions’ physiochemical properties and their composition, yield, and protein recovery. Applying laminar flow (7 LPM) and average plate voltage (±6.5 kV) to 0.14-mm pin-milled flour led to the production of optimal protein concentrate. As a result, the flour’s protein was enriched from 19.9 to 57%, accounting for 62% protein recovery. In addition, the 0.14-mm pin-milled flour had the smallest average particle size (D₅₀), causing its protein particles to collide and gain more charge, enhancing protein enrichment of the NCP fractions. While the yield and protein recovery of the NCP fractions was higher under a strong electric field, adjusting to a higher plate voltage led to quick electrode fouling. It also attracted weakly charged protein-fiber matrices of the cell wall to the NCP fraction rather than the CB fraction, making plate voltage ineffective for improving protein enrichment. According to SEM images of all electrostatically separated fractions under different airflow rates, many starch granules, which had been attracted to the PCP fraction at laminar flow, agglomerated with overcharged protein particles at turbulent flow and ended up in the NCP fraction, thereby reducing its protein enrichment and increasing its average particle size (D₅₀). This optimization study produced uniformly sized yellow pea protein concentrate with high protein and retained bio-functionality, suitable as a novel ingredient in food production systems.