Assistant Professor Howard University WASHINGTON, DC, United States
A novel eco-friendly dry-based tribo-electrostatic separation (TES) technique was examined to fractionate yellow pea flour into protein concentrates. As TES pre-processing operating factors, pin and ferkar milling systems equipped with 0.14 and 0.5 mm screen sizes were selected to investigate the impacts of milling type and the corresponding screen size. Moreover, TES operating factors of airflow rate and plate voltage were statistically assessed to optimize protein enrichment from yellow pea flour. The SEM images and particle size distribution curves illustrated that the fractions collected from the positively charged plate (PCP) and bottom of the fractionation chamber (CB) were depleted of protein and concentrated with starch. In contrast, the negatively charged plate (NCP) was composed of fractionated flour enriched with protein. Through the GLM (general linear models) procedure, 0.14 mm pin milled yellow pea flour treated under laminar flow (7 out of 7-14 LPM) and moderate plate voltage (±6.5 out of ±3 to ±12 kV) was chosen as optimal conditions for protein enrichment on NCP fraction, in which protein content increased from 19.9 to 57%, accounting for 62% of total protein. The mean particle diameter of 0.14 mm pin milled flour was found to be the smallest among the originally milled flours, contributing to the highest surface-to-volume ratio and protein chargeability via collision and consequently the maximum protein recovery on NCP fraction. Large starch-protein agglomerates were observed on NCP fraction at turbulent flow, indicating its adverse impact on inducing intense particle-particle collisions and decreasing the protein content. Although strong electric field improved protein separation efficiency on NCP fraction, it led to electrode fouling, as evidenced by the semi-identical protein contents of flours collected from this fraction at high and low plate voltage values. The conducted study may help develop a more sustainable protein fractionation technique.