Antifoaming action of polyoxyethylene-polyoxypropylene-polyoxyethylene-type triblock copolymers on BSA foams

Antifoaming action and mechanism of polyoxyethylene-polyoxypropylene-polyoxy triblock copolymers (Pluronics) on aqueous bovine serum albumin (BSA) foams were studied. Addition of Pluronic L-62 or L-61 to 4 gl(-1) BSA solution in 4-100 mu M concentrations had a strong antifoaming effect which increased with the Pluronic concentration. It was found that, in spite of the general view that antifoams work effectively only in the heterogeneous phase, the Pluronics acted in the homogeneous phase, i.e. when the copolymer was dissolved in the BSA solution. Surface tension measurements showed that Pluronics adsorb at the solution surface and interact with BSA in the surface layer. Foam experiments revealed that the copolymer antifoams acted primarily at the top of foams where the foam lamellae are the thinnest and the probability of film rupture increased with the film drainage time. Single film drainage observations showed that the BSA solution forms stable foams because it forms rigid foam films. Addition of Pluronic L-62 or F-68 made the protein film mobile and the film thinning rate was much faster than without Pluronic. The film drainage rate was independent of the Pluronic type and concentration, but the films were less stable with L-62 than with F-68. A possible explanation for this is that the polyoxyethylene chains of the F-68 are much longer than in the L-62 (or L-61) and thus the steric repulsion between the polyoxyethylene chains of the adsorbed polymer can produce a positive film disjoining pressure only with the F-68. (C) 1997 Elsevier Science B.V.