Dry Fractionation of Navy Beans by Milling and Air Classification: Protein Enrichment, Particle Size Distribution, and Functional Properties

Abstract

Dry fractionation by milling and air classification produces plant protein concentrates with preserved native functionality. However, limited information is available on the fractionation behavior and functional properties of navy bean (Phaseolus vulgaris L.) protein fractions. This study evaluated the effects of classifier wheel speed (7115, 9920, and 11730 rpm) and air flow rate (2.8 and 3.3 m³/min) on particle size distribution, protein enrichment, processing performance, and functional properties of navy bean protein concentrates. Increasing classifier wheel speed significantly reduced particle size, with D50 decreasing from 21.6 μm at 7115 rpm to 14.4 μm at 11730 rpm (2.8 m³/min). Protein purity increased from 35.0% to 44.9% at 2.8 m³/min and from 33.8% to 43.2% at 3.3 m³/min as classifier wheel speed increased, while yield decreased from 28.3% to 8.0% at 2.8 m³/min due to the stricter separation of finer particles. Oil absorption capacity increased significantly with classifier wheel speed and ranged from 1.00–1.3 g/g protein, whereas water absorption capacity showed no significant differences among treatments. Emulsifying capacity ranged from 57.3–63.9% and emulsion stability from 53.9–57.8%, both improving with higher classifier wheel speeds. Protein solubility remained high (77.5–97.0%), indicating good dispersibility of the protein fractions. Among the conditions evaluated, the combination of 11730 rpm classifier wheel speed and 2.8 m³/min air flow produced the highest protein purity, oil absorption capacity, emulsifying capacity, and emulsion stability. These results demonstrate that milling and air classification can effectively produce navy bean protein concentrates with high protein enrichment and desirable functional properties for plant-based food applications.

Graphical Abstract