Quantitative analysis of binding affinities and characterization of β-lactoglobulin and λ-carrageenan as a function of pH

λ-Carrageenan (λcar) interacted with β-lactoglobulin (βlg) immediately to form βlg-λcar complexes when used as an additive in milk. The formation of complexes is the key process through which to explore the bioapplication of λcar, which is a complicated process and influenced by many factors. In this study, the formation process and effect of pH were ascertained by the binding affinity, hydrodynamic diameter, and secondary structure. Results showed that the interaction was spontaneously exothermic and the complexes were soluble. The binding affinities (Ka) decreased from 9.0 ± 1.3 × 10⁵ to 1.3 ± 0.8 × 10⁵ M^-1 , and the stoichiometry also decreased as the pH was increased from 4 to 7. Furthermore, DLS showed a larger hydrodynamic diameter of the complexes at lower pH. Moreover, the complexes induced a change in the secondary structural components of βlg at lower pH. PRACTICAL APPLICATIONS: The secondary structure of βlg was changed by the interaction of λcar, which resulted in βlg-λcar complexes under acidic conditions. The soluble βlg-λcar complexes showed a good stability against aggregation. Thus, they can enhance the textural properties and stability of acidic dairy drinks, and can be used to accurately formulate ingredients in the food ingredient industry.