How to Balance the Yield and Protein Content of Air-classified Pulse Flour: the Influence of the Restriction Valve

Dry fractionation by air classification is a sustainable process applied to cereals and pulses to produce protein and starch concentrates. The process involves using a series of cyclones equipped with either a classifier wheel or a restriction valve, which allow to separate a coarse starch-rich fraction and a fine protein-rich fraction. In this study, an apparatus with an air restriction valve was used, with the aim of studying the influence of two set-ups of the air classification system, on the protein content, yield, protein separation efficiency, and physicochemical and functional properties of the resulting fractions. The tighter restriction valve set-up (lower air flow and air speed compared to a more opened set-up) caused an increase in the protein content in the fine protein-rich fraction from 53.9% to 61.9%, but the drawback was a 47% yield decrease and a decrease in the protein separation efficiency. The results highlighted that the dry fractionation process should be carefully calibrated in order to balance the yield and the chemical composition (e.g. the protein content) of the fractions. In particular, the more opened set-up was better capable of balancing these two parameters, indicating that a high air flow is necessary for pulse flour. Moreover, the set-up of the restriction valve did not significantly influence effect on the physicochemical and functional properties of the fraction, pointing out that even a protein-rich fraction with a 50% protein content could be successfully used as a food ingredient.