Bovine beta-lactoglobulin (beta-lg) present in milks has been found "in vivo" in complexes with lipids such as butyric and oleic acids. To elucidate the still unknown structure-function relationship in this protein, the structural changes of beta-lactoglobulin variant A (beta-lg A) were investigated in the presence of sodium dodecylbenzenesulfonate (SDBS) as an anionic surfactant using spectrofluorimetry. Subsequently, the retinol binding was investigated by beta-lg in the presence of various amounts of this surfactant as its extrinsic functional binding fluorophore. The comparison of the results allowed for determining the binding of retinol by beta-lg in the presence of SDBS. The results of fluorescence studies showed a higher denaturating effect of SDBS at acidic pH that can be due to the positive charge density of beta-lg at this pH which was calculated using the Henderson-Hasselbalch equation and pK(a) values of its ionizable groups. For each transition curve, the conventional method of analysis which assumed a linear concentration dependence of the pre- and post-transition base lines gave the most realistic values for Delta G(D)(0)(H2O). The value of about 21.6 kJ . mol(-1) was obtained for Delta G(D)(0) (H2O) at various pH from transition curves. The results of retinol binding studies represented the substantial enhancement of retinol binding affinity of beta-lg in the presence of this surfactant at various pH levels. Moreover, the obtained results confirmed that the beta-lg/retinol binding was pH-dependent. (C) 2011 Elsevier Ltd. All rights reserved.