(159as) Sustainable Production of Protein and Fiber Concentrates from Defatted Soybean Flour By Tribo-Electrostatic Separation

The global demand for plant proteins is expected to increase with the current growing population rate. Plant protein isolates are mostly extracted by the conventional wet fractionation methods that involve the use of solvents, alkali and concentrated acids along with elevated temperatures, extreme pH shifts, large volumes of water and intensive energy. Such harsh conditions denature the proteins and have negative impact on protein solubility and functionality. Solvent-free dry separation techniques such as dry milling combined with sieving, air classification or tribo-electrostatic separation (TES) are alternative approaches to produce protein concentrates rather than isolates with an advantage of retaining native bio-functional properties of proteins that can be useful for producing novel ingredients for both food and pharmaceutical industries. Considering the wide range of benefits and applications of plant-derived nutrients, the purpose of this research study is to develop a novel sustainable TES system in a chemical- and water-free environment to concentrate high-quality protein and fiber powders from defatted soybean flour and to optimize the fractionation process through studies at different operating conditions.

Our developed approach is based on different tribo-charging properties of protein vs. fiber particles since proteins have ionizable functional groups such as amino-carboxyl groups and various side chains that result in high-extent chargeability characteristics. A custom-built TES system containing a fluidized bed, a tribo-charging tube apparatus made of PTFE and a plate-type fractionation chamber connected to the positive and negative copper electrodes was custom-designed in our Bioprocess Engineering Research Laboratory at Howard University. To start the separation, the soybean flour was first suspended into a fluidized bed and then charged by physical contact against each other and friction with the tribo-charger tube at laminar (~7 LPM) and turbulent (~15 LPM) air flow rates before being separated in the chamber at three different plate voltages (±1kV, ±3.5kV, ±6.5kV). Protein-rich particles obtained positive charges while carbohydrate-rich particles acquired weak negative charges upon frictional contact with PTFE tribo-charger tube.

We have carefully studied the effects of different impact velocities and applied voltages on the protein/fiber enrichment levels and their equivalent separation efficiencies. Laminar air flow rate was enough to charge the particles without overcharging them in the tube, while high voltage was found to be stronger in detaching the protein bodies from fiber particles. Therefore, the optimal operating setting was determined to be 7 LPM and ±6.5 kV for one separation cycle that resulted in an increase of starting protein and fiber contents from 55.3% and 15.4% to 58.4% and 19.6%, respectively, accounting for 66.5% of the total protein and 25.1% of the total fiber in soybean flour. With this combination of air flow rate and plate voltage, the highest yield of particles with sufficient protein and fiber enrichment was achieved.