PH Profiles in Biochemical Reactors

Abstract

In fermentation cellular growth and product formation are controlled by enzyme catalysed metabolic processes which depend upon local substrate and hydrogen ion concentrations. The steady state attained by intracellular environment is the result of a balance between the rates of enzyme catalyzed reactions involving consumption of substrates and production of products, and the membrane limited mass transfer across the cell membrane. Many enzymatic reactions occurring in vivo or in vitro, involve production and/or consumption of acids or bases which on entering the solution alter the pH of reaction environment. In such reaction systems the enzyme activity is affected as a result of sensitivity of enzyme to the hydrogen ion concentration. The pH deviation from optimal value in such processes is sought to be corrected by neutralising the acidic or basic products. The microenvironmental pH of the cell is then determined by the rates of metabolism, the speed of attainment of the ionic equilibria in the aqueous phase, the ionic fluxes across the cell membrane and the rate of neutralisation of the acid or base in the external medium. In these fermentations it is of interest to relate the microenvironmental pH to that of the external medium and to predict the resulting pH profiles as function of operating and system parameters. In the present study an artificial cell like system producing CO 2 and NH 3 in an unbuffered medium by the enzymatic decomposition of urea by encapsulated urease has been studied to determine the effects of CO 2 desorption and the membrane permeability on the pH trajectories.