Adsorption of Water-Soluble Proteins onto Bubbles in Continuous Foam Separation

Abstract

The enriching mechanism of water-soluble proteins in continuous foam separation was studied. The liquid flow rate and the protein concentration in foam phase were measured at various heights from the interphase between bulk liquid and foam layer, and the intrinsic values at the interface were estimated by the extrapolation method to determine the accurate adsorption density on bubble surface. Ovalbumin (OA) and hemoglobin (HB) were used as the soluble proteins. The solution pHs were varied from 3.5, 4.6 and 6.0 for OA and from 6.0, 6.8 and 8.0 for HB. The experimental isotherms for OA and HB were compared to the Langmuir isotherm, and the two adsorption parameters of the equilibrium constant, K, and the saturated density, γ, at each pH were determined. Both γ values obtained for OA and HB showed maxima at their isoelectric point (i.e.p., pH 4.6 for OA and pH 6.8 for HB). Assuming that OA and HB molecules are spherical in shape and they are adsorbed on bubble surface in a closed packed structure at the saturated condition, the calculated diameters for OA and HB molecules were quite similar to the literature values. The variation in γ for both OA and HB were discussed qualitatively relating to the net charge of protein molecule.2

Variation of saturated surface density of ovalbumin on bubble surface in continuous foam separation

“…The experimental setup for foam separation is almost the same as that used in the previous study [6,21,24]. A schematic diagram of the experimental setup is shown in Fig.…”

“…The procedure for measuring the flow rate of the liquid in foam was the same as it described in the previous study [6,21,24]. The OA solution prepared at a desired concentration or pH was stored in a storage tank.…”

“…In the bubble dispersed phase with the column, the following mass balance is obtained under a steady state at the liquid -foam interface [6]:…”

“…This technique has been studied in many fields, such as chemical/biochemical engineering [1][2][3][4][5][6], analytical chemistry [7,8], wastewater treatment [9][10][11] and so on.…”

“…In our previous study [6], the enrichment of ovalbumin and hemoglobin used as model substances from aqueous solutions were attempted by a foam separation method in a continuous system. The adsorption of the soluble proteins onto the bubble surfaces well followed the Langmuir's adsorption isotherm, and as a result we could obtain the two adsorption parameters, i.e., adsorption equilibrium constant and saturated adsorption density.…”