A study of the conformational changes of β-lactoglobulin in the vicinity of critical point of binary mixed solvents

Abstract

In this study, we present the influence of bovine milk β-lactoglobulin (β-LG) as an impurity on the critical mixture of isobutyric acid (IB) + water (W) using density (ρ) coexistence curve, fluorescence spectroscopy and dynamic light scattering (DLS) measurements. Furthermore, the coexistence curve density data used to obtain the critical exponents (β), which depict the shape of the coexistence curve. Our experimental results explicitly elucidate that the critical region of IBW decreases with an increasing concentration of β-LG. The critical temperature (T_c) of IBW can be modulated by the addition of different concentrations of β-LG. The modulation in the T_c values can be attributed to the β-LG induced interactions of solvent molecules with the residues of β-LG. The observed deviations in the T_c with temperature predict unambiguously the formation of the solvation structure at T_c for the critical mixture in the absence as well as in the presence of β-LG. Our results show that β-LG can significantly affect the critical binary mixture of IBW. On the experimental side and to the best of our knowledge, this is the first experimental evidence that most of the protein entangles in the upper, IB-rich phase.