Interactions of β-lactoglobulin with sodium decylsulfonate, decyltriethylammonium bromide, and their mixtures

The interactions of β-lactoglobulin (BLG) with anionic surfactant sodium decylsulfonate (C 10SO 3), cationic surfactant decyltriethylammonium bromide (C 10NE), and the mixtures of cationic–anionic surfactants (C 10NE–C 10SO 3) were investigated by circular dichroism (CD) and fluorescence methods. At pH 7.0, C 10NE and the C 10NE-rich surfactant mixtures of C 10NE–C 10SO 3 could form precipitates with BLG, while C 10SO 3, equimolar mixtures of C 10NE–C 10SO 3, or C 10SO 3-rich mixtures of C 10NE–C 10SO 3 form homogeneous solutions with BLG. CD observed that both C 10NE and C 10SO 3 could change the BLG structure. The effects of the mixtures of C 10NE–C 10SO 3 on BLG structure depended on the ratio of C 10NE to C 10SO 3. The C 10NE-rich or the C 10SO 3-rich mixtures of C 10NE–C 10SO 3 could significantly affect BLG structure, while the equimolar mixtures of C 10NE–C 10SO 3 exhibited weaker interaction with BLG. Fluorescence measurements showed that both C 10NE and C 10SO 3 could induce the enhancement of fluorescence of BLG, and C 10NE enhanced the BLG fluorescence more than C 10SO 3 did. The effect of the mixtures of C 10NE–C 10SO 3 on the fluorescence of BLG became stronger with the increase of the molar fraction of C 10NE in C 10NE–C 10SO 3 mixtures. C 10NE enhanced the BLG fluorescence more than C 10SO 3 did (a), and the effect of the mixtures of C 10NE–C 10SO 3 on the fluorescence of BLG became stronger with the increase of the molar fraction of C 10NE in C 10NE–C 10SO 3 mixtures (b).