Abstract: Black bean protein isolate (BBPI), obtained by alkali solution and acid precipitation, was treated under different pH conditions (2.0–11.0) for 2 h and then returned to neutral pH condition. The surface hydrophobicity, solubility, secondary and tertiary structures, emulsion stability and rheological properties of BBPI were determined. The results showed that the protein sample treated at pH 5.0 had the lowest solubility and emulsion stability, while that treated at pH values far from 5.0 showed an increasing trend in solubility and emulsion stability, which were better under alkaline conditions. With the increase in acid and alkaline intensity, the unfolding degree of protein tertiary structures increased, and the β-sheet secondary structure transformed to α-helix. The higher the solubility, the lower surface hydrophobicity, which was positively correlated with the β-sheet content but negatively correlated with the β-turn content. With increasing the shear rate from 0.1 to 100 s-1, the apparent viscosity gradually decreased, and the emulsion showed a shear-thinning behavior; with the increase in pH, the apparent viscosity initially decreased and then increased. The dynamic rheological analysis showed that with the increase in angular frequency from 0 to 70 rad/s, the G’ of emulsions stabilized by BBPI treated with different pH values increased. At pH 3.0, the protein had stronger interface viscoelasticity, and the formed emulsion had better interfacial rheological properties. At pH 11.0, the protein was conducive to better oil-water interfacial combination, and displayed the best emulsifying performance.

Key words: black bean protein isolate; pH; surface hydrophobicity; rheological behavior; emulsifying properties