Sustainable extraction of protein from de-oiled soybean cake using choline chloride- glycerol based deep eutectic solvent

The extraction of soy protein from de-oiled soybean cake using deep eutectic solvents is systematically studied as a sustainable alternative to conventional alkali-acid methods. Choline chloride is used as the hydrogen bond acceptor with either glycerol or polyethylene glycol as the hydrogen bond donor in varying molar ratios. Results show that choline chloride: glycerol deep eutectic solvents consistently outperform choline chloride: polyethylene glycol in protein yield due to its higher polarity, greater number of hydroxyl groups, and lower viscosity, which collectively enhances protein solubility and extraction efficiency. The most suited extraction is achieved with a choline chloride: glycerol molar ratio of 1:3 at 60 °C and pH 4.5, yielding 0.28 g protein per g of sample with a protein content of approximately 72%. Statistical analyses including t-tests and one-way ANOVA are performed to validate the credibility and significance of the observed differences. Fourier Transform Infrared Spectroscopy analysis confirms that the extracted protein retains structural features similar to commercial soy protein isolates, while water contact angle measurements indicate increased hydrophobicity compared to reference protein. The extracted protein exhibits higher turbidity, suggesting a greater tendency for protein-protein interactions, and demonstrate functional properties suitable for food applications. Additionally, the extracted protein shows moderate water hydration and enhanced emulsifying stability due to increased surface hydrophobicity. Overall, deep eutectic solvents -based extraction, particularly with choline chloride: glycerol at a 1:3 ratio, offers an environmentally friendly and efficient method for soy protein extraction, producing a protein with desirable structural and functional properties for food and allied industries.