Reinforcing the pea protein isolate-gellan gum composite gels by pH-shifting pretreatment: Emphasizing pH-modulated aggregation behavior and gelation mechanisms

This study aimed to investigate the effects of pH-shifting on the aggregation behavior of pea protein isolate (PPI) and gellan gum (GG), as well as the gel properties and formation mechanism of PPI-GG composite gels. With the pH shifted from 3 to 11, the solubility of PPI decreased at first and then increased, reaching minimum value at pH 5 . PPI-GG allowed for the fastest sol-gel transition at pH 5. In this case, PPI-GG composite gel exhibited the highest dynamic modulus, gel strength (189.00 ± 24.06 g), hardness (631.92 ± 95.14 g), water holding capacity (94.3 ± 3.2 %), and thermal stability. However, steady shear tests revealed structural instability under high shear rates. In contrast, PPI-GG composite gel formed at pH 7 exhibited higher yield stress and lower tan δ, indicating its more stable and homogeneous network structure. Fourier transform infrared spectroscopy revealed that the β-sheet content reached its maximum at pH 5 and progressively decreased as the pH moved away from the isoelectric point. Measurements of sulfhydryl groups and intermolecular interactions indicated that disulfide bonds contributed to gel formation at both pH 5 and pH 7, with a more pronounced effect observed at pH 5. This study provides the first comprehensive analysis of pH-mediated transitions in the physicochemical, structural, and gel properties of PPI–GG composite gels, elucidating the underlying gelation mechanisms across different pH levels and contributing to the rational design and development of gel-based foods with tailored functionalities.