EXPERIMENTAL INVESTIGATION OF STATIC DRAINAGE OF PROTEIN STABILIZED FOAMS - COMPARISON WITH MODEL

Experimental measurements of the transients of the foam-liquid interface for static drainage of foams stabilized by different proteins such as Bovine Serum Albumin (BSA), Human Serum Albumin (HSA) and casein were made. The foam was generated by bubbling nitrogen through protein solution. Foam drainage was found to be faster and the extent of drainage larger for smaller bubbles, larger initial foam heights, larger ionic strengths and for larger bubbling flow rates employed for foam generation. When the same nitrogen bubble flow rate was employed for the generation of foams of different viscosity liquids, the rate as well as the extent Of drainage were found to be larger for more viscous liquids. When the initial liquid holdup profiles were maintained the same by varying the gas flow rate for foam formation inversely to the viscosity, however, the extent of drainage remained the same with the rate of drainage being inversely proportional to viscosity. Drainage rates of foam stabilized by BSA were found to be intermediate at pI of BSA. The rate and the extent of drainage were larger for globular proteins such as BSA and HSA compared to casein. Prediction of the transitions of the foam-liquid interface employing a previously developed model (Narsimhan, 1991, J. Food Eng., 14, 139) compared favorably with experiments for a characteristic bubble size. Because of the broad bubble size distribution in the foam, this characteristic bubble size was found to be different from the mean.