Structural, functional properties, and in vitro digestibility of sunflower protein concentrate as affected by extraction method: Isoelectric precipitation vs ultrafiltration

This study was the first to compare the structural features, functional properties and in vitro digestibility of two protein concentrates produced from defatted sunflower meal via two different three-stage processes (chlorogenic acid removal-alkaline extraction-isoelectric precipitation versus chlorogenic acid removal-alkaline extraction-ultrafiltration; concentrates termed AI-SPC and AU-SPC, respectively). Compared with AI-SPC, AU-SPC with a darker brown color had much higher protein recovery yield and purity, much higher solubility at pH 4–7, higher oil-holding capacity, greater emulsifying and foaming capacities at pH 7 and 9, and slightly lower foaming capacity at pH 3. The bioavailability was higher for AU-SPC after oral-gastric-intestinal digestion. Moreover, AI-SPC occurred as clumps/lumps of particles, whilst AU-SPC appeared as flat blocks with continuous surfaces. AU-SPC was more negatively charged, and had a smaller particle size, less β-sheet, more β-turn, slightly more α-helix structure. These results confirmed the close relationship between protein production methods and its functional properties and digestibility.