Structural and thermal stability of β-lactoglobulin as a result of interacting with sugar beet pectin.

Changes in the structural and thermal stability of β-lactoglobulin (β-LG) induced by interacting with sugar beet pectin (SBP) have been studied by circular dichroism (CD), Fourier transform infrared, and steady-state as well as time-resolved fluorescence spectroscopic techniques. It has been demonstrated that SBP not only is capable of binding to native β-LG but also causes a significant loss in antiparallel β-sheet, ∼10%, accompanied by an increase in either random coil or turn structures. In addition, the interaction also disrupted the environments of all aromatic residues including Trp, Phe, and Tyr of β-LG as evidenced by near-UV CD and fluorescence. When preheated β-LG was combined with SBP, the secondary structure of β-LG was partially recovered, ∼4% gain in antiparallel β-sheet, and Trp19 fluorescence was recovered slightly. Although forming complexes with SBP did not significantly impact the thermal stability of individual secondary structural elements of β-LG, the environment of Trp19 was protected considerably.