Effects of Different Fermentation Conditions on Growth and Citric Acid Production Kinetics of two Yarrowia lipolytica Strains

S. Karasu-Yalcin, M. Tijen Bozdemir and Z. Yesim Ozbas

Abstract
In this study, effects of initial pH, temperature, initial ammonium chloride concentration and initial concentration of various minerals on growth and citric acid production kinetics of two Yarrowia lipolytica strains were investigated in shake flask batch experiments. Specific growth rate and citric acid production rates were correlated with each one of the investigated parameters by using non-linear regression analysis. Maximum citric acid concentration was obtained at initial pH 7.0 and 5.2 for Y. lipolytica NBRC 1658 and the domestic strain 57, respectively. The highest citric acid production yield was obtained at 30 °C for both of the strains. Maximum citric acid concentrations and production rates were determined in the medium containing 2 g L–1 of ammonium chloride. Inhibition effects of iron and copper salts on citric acid production were found. Addition of manganese salt caused a decrease in citric acid production. Maximum citric acid concentration obtained by Y. lipolytica 57 increased from 37.66 g L–1 to 41.63 g L–1 by addition of 0.008 g L–1 of zinc sulphate into the fermentation medium.

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Keywords
citric acid, Yarrowia lipolytica, batch fermentation, pH effect, temperature, mineral salts