STUDIES ON CITRIC-ACID PRODUCTION WITH IMMOBILIZED YARROWIA-LIPOLYTICA IN REPEATED BATCH AND CONTINUOUS AIRLIFT BIOREACTORS

Citric acid was produced from glucose in repeated-batch shake-flask and continuous air-lift cultivations by calcium-alginate-immobilized Yarrowia lipolytica A-101 yeast. The medium composition was systematically studied in a batch system by using experimental design and empiric modelling. The highest citric acid product concentration of 39 g/l was reached with a medium containing 150 g/l of glucose, 0.105 g/l of potassium dihydrogen phosphate, 0.84 g/l of magnesium sulphate and 21 mg/l of copper sulphate (5.2 mg/l of copper). The results were further improved by hardening the alginate carrier beads with glutaraldehyde, and by activation of the immobilized biocatalyst in a nutrient solution. Iii continuous air-lift bioreactors with varying height-to-diameter ratio the highest productivity of 350 mg/l per hour with a dilution rate of 0.023 1/h and a citric acid product concentration of 12 g/l was reached with a ratio of 3.