The effects of pH and NaCl concentration on the structure of β-casein from buffalo milk

Abstract

In the present study, we aimed to investigate the effects of pH and sodium chloride (NaCl) concentration on the structure of β-casein (β-CN) purified from buffalo milk using circular dichroism (CD), intrinsic tryptophan, and anilino-8-naphthalene sulfonate (ANS) fluorescence spectroscopy. We found that NaCl concentration played a critical role in the stability of the secondary structure of β-CN. The CD negative peak had a redshift as the NaCl concentration was increased and accompanied by a decrease of β-sheet content and an increase of α-helix content. ANS fluorescence spectroscopy also indicated that higher NaCl concentration and lower pH significantly affected the tertiary structure of β-CN. Dynamic light scattering (DLS) results showed that the particle size of buffalo β-CN had a blueshift, and then a redshift within the pH range of 5.0–7.5, and it showed a redshift when the NaCl concentration was increased.