Immobilized yeast cell（Candida lipolytica MX 9-11 R3） was prepared by entrapping the whole cell in calcium alginate matrix. The fermentative production of citric acid from glucose was studied using this immobilized yeast cell in a fluidized-bed batch reactor. One could more or less prevent the cell growth using glucose as the sole nutrient and thus eliminating other nutrients necessary for the cell mass doubling. The productivity of citric acid was remarkably influenced by reaction temperature, pH, and air flow rate in fluidized-bed batch reactor. The optimal conditions for the citric acid production were found to be 28 ℃ and pH 6 as compared with those of homogeneous case, i.e. 26 ℃(Tabuchi), 30 ℃(Nakanishi), and pH 5(Marchal), pH 6.5(Nakanishi). The increased air flow rate resulted in an enhanced citric acid production possibly due to the increased dissolved oxygen concentration and the decrease in mass transfer resistance.
The intentional addition of CO₂ gas into the air supply to the fluidized-bed batch reactor gave a better citric acid productivity in certain concentration ranges. The optimal CO₂ content was found to be 16 %（v/v）.