COLLOIDAL GAS APHRONS - A NOVEL-APPROACH TO PROTEIN RECOVERY

Sebba (1987) defined colloidal gas aphrons (CGA) as microbubbles stabi lized by surfactant layers, which are created by stirring surfactant s olutions at speeds greater than a critical value. A high shear impelle r is used for stirring and critical values for the impeller speed must be exceeded to create these stable gas liquid dispersions (typically >5000 rpm). Although there have been no previous reports of direct pro tein recovery using CGA, it is likely that, with appropriate choice of surfactant, proteins should adsorb to these surfactant bubbles by mea ns of electrostatic and/or hydrophobic interactions. This is the basis of this study, in which the use of CGA for protein recovery from aque ous solution is considered. A surfactant which has been characterized previously for generation of CGA was chosen (Jauregi et al., 1997), i. e., the anionic surfactant sodium bis-(2-ethyl hexyl) sulfosuccinate ( AOT). Lysozyme, a well-characterized protein, was chosen as the protei n to be recovered. Lysozyme was recovered successfully from aqueous so lution using CGA generated from AOT. At optimum conditions, lysozyme r ecovery, enrichment ratio, and separation ratio were 95%, 19 and 302 r espectively, with enzyme activity maintained. These results indicate t he exciting potential of this technique. A wide range of process condi tions including initial concentration of protein and surfactant, surfa ctant/protein molar ratio, pH, and ionic strength were considered. Hig h recoveries and enrichments were generally obtained at protein concen trations less than or equal to 0.41 mg/mL, and surfactant concentratio ns >0.11 mg/mL. However, at high ionic strength (0.29 M) poor separati on and recoveries were obtained at low protein concentrations (counter ions diminishing electrostatic interactions between protein and aphron s at this condition). In general, (n(s)/n(p))(a) was determined to be between 10 and 16 for experiments in which high levels of recovery/sep aration parameters were found. For most conditions, protein precipitat ion was observed; however, this precipitate could be resolubilized wit hout loss of enzyme activity. (C) 1998 John Wiley & Sons, Inc.