Dry protein fractionation by Tribo-electrostatic separation: Charge polarity, charge magnitude, and governing factors.

The global transition to sustainable protein production is increasing interest in resource-efficient fractionation technologies for bio-based materials. Conventional wet fractionation methods rely heavily on water, chemical reagents, and energy-intensive steps, causing serious environmental and economic problems. Tribo-electrostatic Separation (TES) has emerged as a promising solvent-free dry separation technology that uses charge-based separation to concentrate protein- and carbohydrate-rich fractions from finely ground powders. In TES, particles acquire electrical charges through repeated contact interactions and are separated in an external electric field based on the polarity and magnitude of the charges. Despite this potential, TES performance varies significantly across studies, primarily due to a lack of mechanistic understanding of triboelectric charging in heterogeneous food systems. This paper critically reviews TES across plant, animal, insect, and agro-industrial raw materials. In particular, it focuses on the roles of charge polarity, which governs particle trajectories, and charge magnitude, which determines the strength of electrostatic interactions. Furthermore, it systematically analyzes how material properties, particle characteristics, equipment design, operating conditions, and environmental factors influence these parameters. The analysis demonstrates that TES performance is governed by the complex interactions among charge polarity, magnitude, and particle dispersion behavior, rather than by a single parameter. This mechanistic understanding provides a foundation for improving the design, optimization, and scalability of TES processes for sustainable protein separation.