Structural changes in β-lactoglobulin by conjugation with three different kinds of carboxymethyl cyclodextrins

β-Lactoglobulin-carboxymethyl cyclodextrin (β-LG-CMCyD) conjugates were prepared by using water soluble carbodiimide. Three kinds of CMCyDs differing in molecular mass were used to investigate the effects of different CMCyD contents, net charge and hydrophobicity on the structural changes in β-lactoglobulin. The effect of CMCyDs on the structure of β-lactoglobulin was utilized to investigate the contribution of hydrophobic interactions to the stability of the protein. Spectroscopic studies suggested that the conformation around had not changed in either conjugate but the α-helix content of β-LG-CMCyD conjugates had markedly increased as compared with that of β-lactoglobulin. The differential scanning calorimetry technique confirmed that the addition of one glucose unit in β-LG-CMCyD conjugates, enthalpy change of calorimetry decreased and the denaturation temperature of each conjugate was higher than that of native β-lactoglobulin. The heat contents agreed well with the conformational transition measured by molar ellipticity at 222 nm (θ]₂₂₂) and Stoke's radius (R_S) values. Therefore, hydrophobic forces play an important role in stabilizing and shielding of the β-LG-CMCyD conjugates.