No abstract

No abstract

Recently, the respiratory quotient (RQ) of microbes measured in situ in a fermentor by exit-gas analysis has been used successfully, for instance, in a fed-batch culture of baker's yeast as a criterion to control the feeding rate.'-3 It is significant here t o keep RQ values close t o unity throughout; any deviations of RQ from unity give rise to deterioration of the cell growth yield.However easy it might be to keep RQ values around unity by controlling the feeding rate, the question of whether or not RQ values determined by gas analysis at the fermentor exit could generally represent those in vivo deserves attention. Indeed, for a fermentation carried out at an alkaline side, gas analysis would give RQ values that differ remarkably from true values because of the medium's "storage" of C02 released from microbes. The purpose of this communication is to make clear those factors that would affect true RQ values in the analysis of exit gas from a fermentor. THEORETICAL CONSIDERATIONS Gases Dissolved in LiquidTaking for granted that 0, and CO, are the sole components of gas in an aerated fermentor, concentrations Ci of these components dissolved in liquid (taken as water) are assumed to be always in equilibrium with their partial pressures regardless of space, either free space above liquid or within gas bubbles. Taking an average of Ci throughout the liquid as Fitwhere Hi is the proportionality constant of absorption for the P is the total pressure of gas;x i is the mol fraction of ith component; and i is 0, or CO,.ith component;* To whom all correspondence should be. addressed. So far as the dissolution of C 0 2 in liquid is dealt with hereafter, the concentration of total carbon rko2 defined below, will be considered: provided that = 1 + K , l P H + K , K,102pH 7&02 = HC0,t Mass Balance in a FermentorAssuming complete mixing in liquid and gas phases, respectively, the rate of change in gas fraction of the ith compo-CCC 0006-3592/90/050534-05$04.00

No abstract

No abstract