Partition of adsorbed and nonadsorbed bovine serum albumin in dodecane-in-water emulsions calculated from front-face intrinsic fluorescence measurements

Front-face fluorescence spectroscopy was used to estimate directly the extent of adsorption of bovine serum albumin (BSA) onto dodecane-water interface in dodecane-in-buffer (pH 7.6, 0.1 M) emulsions. The wavelength of the emission maximum (lambda(max)) of adsorbed BSA was blue-shifted (-15 nm) as compared to that of nonadsorbed BSA in phosphate buffer (Castelain and Genot, 1994). The concentrations of adsorbed and nonadsorbed protein in emulsions and the partition of BSA between cream and serum were calculated from volume, oil, and protein balances and lambda(max) measured on emulsions (oil volume fraction = 0.5 and 0.16; 0.1-36 g of BSA/L aqueous phase), creams, and serums. In emulsions containing 0.5 g of BSA/L, the protein was totally adsorbed at the interface and the serum phase did not contain any protein. When the protein concentration increased, the nonadsorbed BSA concentration increased more rapidly than the adsorbed one. However, serum phase contained adsorbed proteins at concentrations which cannot be neglected.