Dry fractionation for production of functional pea protein concentrates

Abstract

Dry milling in combination with air classification was evaluated as an alternative to conventional wet extraction of protein from yellow field peas (Pisum sativum). Major advantages of dry fractionation are retention of native functionality of proteins and its lower energy and water use. Peas were ground by impact (ZPS50) and jet milling (AFG100) at various classifier wheel speeds to provide pea flours with different particle size distributions, protein contents and damaged starch levels. Peas were milled under various conditions to maximally disentangle starch granules from the surrounding protein bodies. The optimal milling conditions were confirmed by particle size analysis and scanning electron microscope imaging. Too extensive milling, e.g. using ultrafine impact or jet milling, resulted in very fine flours (with D0.5<10μm) with poor flowability, whereas ultrafine jet milling led to an increased percentage of damaged starch. Subsequently, air classification was applied to separate small fragments (primarily protein bodies) from the coarse fraction (starch granules) to obtain enriched protein concentrates. Protein concentrates were obtained with protein contents between 51% and 55% (w/dw) and a maximum protein recovery of 77%. Deviating cut-off size for air classification could be ascribed to build-up of material between the vanes of the classifier wheel. Finally, water holding capacity (WHC) tests were used to evaluate the functional properties of the pea protein concentrates. A liquid pea concentrate comprising 26% (w/w) of protein could be prepared from dry pea concentrates containing more than 30% (w/dw) of pea protein. This was explained by the high solubility of pea protein in its native state. After heat treatment of pea protein concentrates, a gel with a high WHC of 4.8g water (w/w) was obtained, which decreased with increasing protein content. Functional properties of the pea protein concentrates are interesting for preparation of high-protein foods or for replacement of egg protein functionality.