Effects of natural deep eutectic solvents’ hydration level, choice of hydrogen bond donor and ultrasound treatment on the extraction, antinutritional components, structural properties and functionality of canola protein isolates

Canola meal is an inexpensive source of sustainable protein; however, due to its high contents of anti-nutritional components, acquiring high-quality canola protein using conventional extraction methods is often challenging. Alternatively, Natural deep eutectic solvents (NDESs) offer an enormous potential for canola protein extraction, since they may be tailored to maximize the extraction of protein while minimizing the extraction of anti-nutritional components. However, their relatively higher cost compared to conventional solvents, along with insufficient understanding of their effects on protein properties, are the two key issues hindering the large-scale adaptation of NDESs. Therefore, in a systematic attempt to address these issues, 18 extraction treatments, half of which paired with sonication, were performed to obtain canola protein using two groups of NDESs, choline chloride-glucose-water (CG) and choline chloride-water (C), with varying water contents of 30-90%. The highest protein extraction efficiencies were observed at water contents of 60% for CG group and 90% for C group at 50.28% and 45.28%, while sonication improved these efficiencies to 60.68% and 58.11%, respectively. Increased solvent hydration and sonication were also effective in the reduction of phenolic compounds and phytic acid contents, especially in CG group. Despite the notable increase in solvents’ viscosity and density, combination of glucose and water as hydrogen bond donors proved more effective for protein extraction compared to water alone. Moreover, solvent water content and sonication affected the protein’s tertiary structure, particle size distribution, aqueous solubility and emulsion and foam stability, with the strength and flexibility of the NDESs’ nanostructure possibly affecting the protein fold and aggregation. Overall, pushing NDESs to their upper hydration limit (60% in the case of CG group), which could significantly reduce solvent production and recovery costs, and sonication have been effective strategies for acquiring high-quality canola protein and may be used for other protein sources in the future.