Rheokinetic Analysis of Protein Films at the Air−Aqueous Phase Interface. 1. Bovine Serum Albumin Adsorption on Ethanol Aqueous Solutions

The dilational rheological properties and surface tension of bovine serum albumin (BSA) adsorbed at the air−aqueous phase interface were measured as a function of time, protein concentration (1 × 10-1−3 × 10-3% w/w), and subphase composition (aqueous ethanol solutions from 0 to 2 M). The temperature was maintained at 20 °C. Adsorbed BSA films on water and aqueous ethanol solutions exhibited rheological properties that were mainly elastic and not very frequency dependent. The time dependence of surface tension and surface rheological properties was related with the rate of protein adsorption and the influence of ethanol on competitive adsorption. This phenomenon as well as protein−ethanol interactions could be supported by a significant reduction of the surface dilational modulus as either ethanol concentration increased (at constant BSA content) or BSA concentration decreased (at constant ethanol content). Circular dichroism measurements showed no significant change in the secondary structure of BSA in the presence of ethanol, at the concentrations used in these experiments. Keywords: Superficial dilational rheology; adsorption; surface properties; bovine serum albumin; air−water interface