Dry fractionation is an environmentally friendly method for producing plant protein concentrates by ultrafine grinding and air classification, yet it has notable technical limitations compared with conventional wet extraction.
Upper limit of protein enrichment
Full dissociation of protein bodies from starch granules cannot be achieved by mechanical comminution alone, since some protein remains physically embedded within plant cell fragments. Maximum protein content of dry-fractionated concentrates usually falls in 55–75% (dry basis), much lower than wet-processed protein isolates (>80%). It cannot reach isolate-grade purity.
High sensitivity to raw material properties
Separation performance heavily depends on seed variety, maturity, moisture, and pre-treatment. Excess moisture causes particle agglomeration and weakens air classification. Over-dried beans lead to excessive ultrafine dust, possible protein denaturation and handling risks. Minor variation in feedstock creates inconsistent final protein content.
Co-separation of fine impurities
The protein-rich fine fraction unavoidably contains residual fine starch, micronized fibre and native ash. Tiny starch particles with similar aerodynamic behaviour to protein fines are difficult to separate by air classification, limiting product purity. Seed coat fragments also increase ash and darken powder colour.
Particle size and functional trade-offs
To liberate protein bodies, ultra-fine milling is required. Over-grinding may damage native protein bodies and negatively impact some functional traits like emulsification or foaming. In addition, ultrafine powder raises flowability issues, dust hazards and packing challenges.
Limited flexibility for high-value purification
Dry fractionation cannot remove soluble anti-nutritional components (phytic acid, saponins, tannins) effectively. Those compounds stay in the protein fraction, which may reduce digestibility or cause off-flavours. Wet extraction can wash out such substances, while dry routes lack this purification step.
Scaling and operational constraints
Multi-product production faces cross-contamination risks. Air classifier efficiency is sensitive to feed rate, rotor speed and air flow; process parameters require tight, continuous control. Production capacity is often lower than large-scale wet extraction lines.
