Recovery of proteins from soybean oil-body wastewater at various pH levels and their structural and functional characterization

Soybean oil-body extraction produces large amounts of protein-containing wastewater, which wastes proteins and pollutes the environment. Herein, we investigated protein recovery from the wastewater generated during soybean oil-body production using the alkaline-extraction–isoelectric-point-precipitation method at various alkaline pH levels. We also investigated the effects of varying alkaline-extraction pH on the basic composition and physicochemical, rheological, and thermal properties of the recovered proteins. The basic composition showed that protein recovery increased with increasing pH, with a 58.88% recovery at pH 11, and that protein purity decreased above pH 10. Structural analysis using FT-IR spectroscopy showed that the α-helix predominance decreased with increasing pH, while β-sheet predominance exhibited the opposite trend. Proteins recovered at pH 8 and 9 were more soluble than those recovered at pH 10 and 11. Proteins recovered at pH 9 exhibited the highest emulsification (p < 0.05) while those recovered at pH 11 afforded the best gelation. The extraction pH has an essential effect on the structural and functional properties of proteins; maximizing value and minimizing waste during soybean processing by recovering functional proteins from wastewater are industrially applicable.