Monellin is a protein known to have a very high specificity for the human sweet taste receptor. It has been isolated from African berries and is approximately 100,000 times sweeter than sucrose on a molar basis. In this study, fed-batch cultures for the overproduction of monellin using recombinant Saccharomyces cerevisiae, which contains a glucose repressible ADH2/GAP(alcohol dehydrogenase 2/ glyceraldehyde 3-phosphate dehydrogenase) hybrid promoter, were carried out at pH 5.0 for 48 hours with constant feed rates from 0.10 to 0.50mL/min. The feed glucose concentration was 370 g/L. The best result was obtained when the feed rate was 0.14 mL/min with a monellin concentration of 188.64 mg/L. Two stage fed cultures were also carried out with the feeding of glucose at 0.14 mL/min and a secondary feeding of ethanol in the second stage. When ethanol feeding was started with the glucose feeding ceased at 35 hours, the highest monellin concentration of 289.36 mg/L was obtained. Another series of fed-batch cultures with the feed rate fixed at 0.14 mL/min were carried out for five different pH`s, that is, 3.5, 4.0, 4.5, 5.0 and 6.0. The highest monellin concentration of 252.75 mg/L was obtained at pH 4.0. The two stage culture was repeated at pH 4.0 expecting a synergy effect of the secondary feeding of ethanol and the optimized pH. But, no significant synergy effect was observed. A further study on the simultaneous optimization of the pH and feeding strategy is in need.
