Pea protein and high methoxyl pectin were used as raw materials to prepare the pea protein-high methoxyl pectin (PP-HMP) complex with different pH, and the effects of pH on the turbidity, particle size, potential, emulsifying activity, and stability of the PP-HMP complex were studied. Meanwhile, the structure of the complex was characterized by fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). Results showed that the PP-HMP complex system existed as the insoluble complex, soluble complex, and co-soluble state at pH 3.0, 6.0, and 8.0, respectively. Compared with pH 3.0 and 8.0, the absolute value of zeta-potential, emulsifying activity, and stability of the PP-HMP complex at pH 6.0 were higher, and no stratification occurred after 24 days. FTIR and fluorescence spectra showed that PP and HMP combined through hydrophobic interaction and hydrogen bond at pH 6.0. Compared with PP, the relative content of β-turn and α-helix of the PP-HMP complex at pH 6.0 increased, the exposure of tryptophan residues decreased, and the structure became more orderly and compact. According to TEM results, compared with pH 3.0 and 8.0, the PP-HMP complex exhibited a structure with more uniform size dispersion and more regular morphology at pH 6.0. The PP-HMP complex at pH 6.0 was suitable for the preparation of emulsion. The results provided a reference for expanding the application of the PP-HMP complex in food.
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