BUBBLE AND FOAM CONCENTRATION OF CELLULASE

Experiments were conducted to determine the effect of pH and sparging- gas composition on the bubble and foam separation of an aqueous protei n solution. Cellulase was chosen as a model system that provided its o wn foam, unlike the previously studied invertase and amylase systems, which did not produce significant foaming. A 1-L graduated cylinder wa s used as the column into which the sparging gas (CO2 or air) was intr oduced. Contact between the rising sparging gas and the bulk solution was espected to lead to a protein concentration gradient (bubble fract ionation) within the solution, as it did previously for yeast invertas e (1). A concentration gradient in the cellulase bulk solution was not observed with either air or CO2, however, but a high concentration wa s observed in the foam layer above the liquid solution (foam fractiona tion). With CO2 sparging, the bulk foam concentration reached a peak o f eight times the solution's concentration at pH=5. When foam-top samp les were collected, moreover, the concentration was as high as 220 tim es the bulk solution's concentration, suggesting a concentration gradi ent within the foam. Exposure to the air seems to reduce the viability of the cellulase harvested in the foam, presumably because of cellula se oxidative deactivation. Oxidative deactivation, if found to be cont rolling, may perhaps be minimized through the use of an inert sparging gas and foam blanketing atmosphere.