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

Experimental measurements of the transients of the foam-liquid interfa ce for static drainage of foams stabilized by different proteins such as Bovine Serum Albumin (BSA), Human Serum Albumin (HSA) and casein we re made. The foam was generated by bubbling nitrogen through protein s olution. Foam drainage was found to be faster and the extent of draina ge larger for smaller bubbles, larger initial foam heights, larger ion ic strengths and for larger bubbling flow rates employed for foam gene ration. When the same nitrogen bubble flow rate was employed for the g eneration of foams of different viscosity liquids, the rate as well as the extent Of drainage were found to be larger for more viscous liqui ds. When the initial liquid holdup profiles were maintained the same b y varying the gas flow rate for foam formation inversely to the viscos ity, however, the extent of drainage remained the same with the rate o f drainage being inversely proportional to viscosity. Drainage rates o f foam stabilized by BSA were found to be intermediate at pI of BSA. T he rate and the extent of drainage were larger for globular proteins s uch as BSA and HSA compared to casein. Prediction of the transitions o f the foam-liquid interface employing a previously developed model (Na rsimhan, 1991, J. Food Eng., 14, 139) compared favorably with experime nts for a characteristic bubble size. Because of the broad bubble size distribution in the foam, this characteristic bubble size was found t o be different from the mean.