Valorization of sunflower (Helianthus annuus L.) and canola (Brassica napus L.) meals through protein coprecipitation: physicochemical, functional, and structural characterization

Abstract

Canola–sunflower protein coprecipitates (CSPoCos) were prepared using different flour ratios, and their physicochemical, functional, and structural properties were analyzed. The crude protein content of CSPoCos ranged from 88.19% to 91.21%, which was higher than that of canola protein precipitate (CPoPc, 82.25%) and sunflower protein precipitate (SPoPc, 86.19%). In addition, protein coprecipitation (PoC) increased the apparent and compact densities and Carr and Hausner indices while decreasing the particle size and modifying the morphology, which were measured through dynamic light scattering and scanning electron microscopy, respectively. Glutelins (52.71–60.30%) were the major protein fraction in CSPoCos. In addition, PoC increased the water holding capacity, oil holding capacity, least gelation concentration, emulsifying activity index, foam capacity and foam stability. The improvement in these functional properties could be due to the formation or combination of various covalent and non-covalent interactions between the individual protein sources. Moreover, PoC modified the secondary and tertiary protein structures of CSPoCos, which was manifested by a significant increase (p < 0.05) in surface hydrophobicity, in comparison to CPoPc and SPoPc. On the other hand, the values for in vitro antioxidant capacity, in vitro digestibility, sulfhydryl groups and disulfide bridges of the CSPoCos were higher than those of CPoPc. Electrophoresis revealed that CSPoCos had subunits with molecular weights ranging from 15 to 49 kDa. Overall, CSPoCos had better functional properties than single canola and sunflower proteins, making the application of PoC an attractive alternative for obtaining protein powders with improved qualities for use as food ingredients.