Abstract
Factor analysis was applied to batch shake-flask fermentation for cytochrome P-450 by S. cerevisiae N.C.Y.C.240 allowing a screening of the experimental variables temperature, pH,fractional filling of the flask and the initial concentrations of glucose,yeast extract, mycological peptone and sodium chloride. All the variables submitted to the factor analysis were found to be relevant to the cytochrome P-450 cost-yield. The cost-yield of the cytochrome P-450 in S. cerevisiae N.C.Y.C.240 was then optimised in shake-flask with respect to all of the above-mentioned culture conditions except the fractional filling of the flask, using a half-replicate 26 factorial and steepest ascent methods to locate the area containing the optimum cost-yield and using a rotatable composite design to find the optimum values of the experimental variables at the point of optimum yield. The enzyme cost-yield was improved by 125% over that of earlier workers and was influenced mainly by the concentration of the mycological peptone in the medium and the pH. Optimisation by the same methods using different numbers of variables was then carried out on the variables temperature, pH, air flow rate, impeller speed, inoculum size and the initial concentration of glucose of the batch fermentation for cytochrome P-450 by the yeast S. cerevisiae N.C.Y.C.754, the high-yielding component of S. cerevisiae N.C.Y.C.240, in a 4-litre stirred-tank fermenter which was equipped with a microprocessor control in the final part of the work. The optimisation gave a 73% improvement in the cytochrome P-450 volume-yield. The enzyme yields were strongly affected by the dissolved oxygen availability, which was controlled via the impeller speed. The accuracy of the microprocessor control was largely responsible for the success of this optimisation. Optimisation of the time-profiles of the variables temperature, pH and impeller speed predicted a further improvement of 113% but this has not been tested due to a failure in the medium.