pH value and ionic strength effects on the adsorption kinetics of protein/phospholipid at the chloroform/water interface

The adsorption kinetics of beta-lactoglobulin in an aqueous buffer solution in the presence of phospholipid, L-alpha-dipalmitoylphosphatidylethanolami ne (DPPE), dissolved in chloroform, has been investigated by using a penden t drop technique. The dynamic interfacial tension for the mixed beta-lactog lobulin/phospholipid layer was measured as a function of time at a constant phospholipid concentration, C-DPPE = I x 10(-6) M. Experimentally it has b een found that increase of ionic strength of aqueous solution can enhance t he adsorption rate of the protein. However, the larger pH value leads to th e adsorption process being reduced. When the protein concentration was incr eased up to 3.8 mg l(-1), the effect of the salt concentration on the adsor ption can be neglected and the protein dominates principally the adsorption process. In the acid aqueous solution, pH 5, approaching equilibrium time of adsorption for protein was around 1300 s and twice longer than in the ba se subphase, pH 8. However, the equilibrium interfacial tension was indepen dent on the pH value. The salt concentration and pH value effects show that both the electrostatic interaction and hydrophobic effect make the mixed l ipid/beta-lactoglobulin layer stable at the liquid/liquid interface. (C) 20 00 Published by Elsevier Science B.V. All rights reserved.