Protein denaturation during high-speed grinding mainly originates from frictional heat, excessive mechanical shear, and over-comminution. The following process and equipment strategies protect native protein structure while achieving targeted particle liberation for dry fractionation.
Control grinding temperature rise (primary measure)
Friction between particles and rotor/stator generates heat, the leading cause of thermal denaturation.
Apply inert gas or cold air feed into the grinding chamber to continuously remove frictional heat; keep powder temperature below 40 °C.
Install temperature sensors linked to PLC interlock: automatically reduce feed rate or pause operation if the outlet powder temperature exceeds the threshold.
Avoid running the mill empty; stable material feed forms a protective particle bed and lowers peak friction.
Adopt selective, low-shear grinding principle instead of over-grinding
High shear force can mechanically rupture protein bodies and unfold protein molecules.
Tune mill parameters to liberate protein bodies from starch granules, not pulverise protein bodies themselves. Reduce rotor peripheral speed where feasible while maintaining sufficient dissociation.
Limit residence time inside the grinding chamber. Short impact exposure minimises cumulative mechanical stress on protein particles.
Avoid repeated regrinding of fines; recirculate only coarse middling fractions, not already liberated protein fines.
Precisely regulate raw material moisture content
Moisture acts as a plasticiser and affects fracture behaviour.
Maintain raw legume moisture in an optimal narrow window (8–11% for peas and chickpeas). Too dry material becomes brittle and creates extreme impact stress; excess moisture causes agglomeration and requires stronger grinding force.
Pre-condition beans with controlled humidification/dehumidification before milling to stabilise particle fracture characteristics.
Equipment and mechanical optimisation
Choose low-shear milling types for plant protein selective liberation, rather than high-energy impact mills that deliver intense particle collision.
Reduce metal contact and local hot spots: use polished rotors and liners; avoid damaged or rough mill surfaces that create concentrated friction.
Balance airflow: sufficient transport airflow quickly carries finished fines out of the grinding zone, preventing overexposure to repeated impacts.
Process monitoring and operational rules
Continuously monitor PSD, outlet temperature, and protein solubility as real-time indicators of denaturation. A sudden drop in solubility signals structural damage.
Limit continuous run cycles; implement intermittent cooling if sustained high throughput causes heat accumulation.
Prevent particle over-refinement: set a hard particle size limit to stop over-milling beyond the target D90.
Lower grinding intensity may reduce liberation efficiency, leading to higher residual starch in protein fines. A balanced operating window must be established between protein structural preservation and separation performance for air classification.
