The effect of Hofmeister series anions on the critical overlap concentration of soybean isolate protein

The influence of different concentrations of Hofmeister series anions on the critical overlap concentration (c*) of soybean isolate protein (SPI) was investigated, along with its potential mechanisms. Techniques including SDS-PAGE electrophoresis, endogenous and exogenous fluorescence spectroscopy, circular dichroism spectrum, Fourier infrared spectroscopy, and solubility analyses were employed. Results demonstrated that higher concentrations of various anions within the solution had an impact on the protein's secondary structure, in line with the principles of the Hofmeister series. This led to a decline in the α-helix proportion and a concomitant increase in the ratio of β-sheets and random coils. Consequently, the protein's structural integrity was compromised, revealing more hydrophobic groups. This alteration in turn affected protein solubility, ultimately influencing the c* of SPI. Furthermore, analysis of scanning electron microscopy images indicated that the introduction of anions indeed influenced the degree of aggregation and the visual characteristics of SPI, with this aggregation trend closely mirroring that of the Hofmeister series anions. In conclusion, the Hofmeister series anions were found to modulate the c* of SPI by inducing changes in the protein's structural arrangement and functional properties.