Abstract: The effect of pH-shifting treatment on the structure of Cyperus esculentus L. protein was studied by Fourier infrared spectroscopy, fluorescence spectroscopy, UV absorption spectroscopy and 8-anilino-1-naphthalene sulfonate (ANS) fluorescence probe emission spectroscopy. Furthermore, the effect on the emulsifying properties of C. esculentus L. protein was analyzed by measuring changes in the surface hydrophobicity, solubility, turbidity and particle size. The results showed that the content of β-sheet decreased, the relative content of α-helix increased significantly and the contents of β-turn and random coil increased slightly as the pH increased. The average particle size of the protein decreased with increasing alkaline pH, the particle size distribution gradually changed from bimodal to monomodal, indicating that more uniform dispersion of the protein. Fluorescence and UV absorption spectroscopy showed that pH-shifting treatment resulted in protein conformational changes; the polypeptide chains in the protein molecule were partially folded, hydrophobic groups were exposed, and the protein structure became more stretched under alkaline pH conditions. As the pH increased, the turbidity decreased significantly, indicating that the protein molecule became more dispersed. The surface hydrophobicity and emulsion stability of the protein first decreased and then increased with increasing pH, indicating that the protein structure was unfolded with increasing alkaline pH. In addition, hydrophobic groups buried inside the protein molecules became exposed, accompanied by an increase in the surface activity and emulsifying activity. These results showed that pH-shifting treatment could change the structure and emulsifying properties of C. esculentus L. protein.

Key words: Cyperus esculentus L. protein; pH-shifting treatment; structural property; emulsifying properties