Air Classification of Plant Proteins

Dry milling followed by air classification has been widely adapted as a sustainable and energy-friendly approach for enrichment of plant proteins from various agro-materials including legumes, oilseed meals, cereals, and brans. Dry milling is a critical stage as it should optimally reduce the size of protein particles to fine levels while disentangling them from the remaining coarse starch- and/or fiber-enriched particles. Fractionation of the fine protein-rich particles from the coarse carbohydrate-rich particles can be performed as a function of their size and density through air classification. Centrifugal air classifiers are among the most commonly used modern classifiers for partial separation of plant proteins from various agro-materials. Protein enrichment level and its separation efficiency are affected by the milling types and intensities as well as air classifier wheel speeds. While moderate to intense milling speeds of ~4000 rpm were found optimal in maximizing protein enrichment of starch-rich legumes, mild milling speeds of ~1000 rpm or less were essential for optimal protein enrichment of non-starch legumes and oilseed meals. Air classification utilizes a water- and chemical-free environment with no high temperature stress and pH shifts and can produce a variety of fractions with unique functional properties with applications in novel food production systems such as 3D food printing and space foods. Air classified protein concentrates fractionated at their native states exhibited low viscosity, but improved solubility, emulsifying and foaming properties compared to wet-fractionated protein isolates/concentrates. Air classified protein-depleted fractions also exhibited relatively high water holding capacity (WHC) and gelatinization behavior.