Enhancement of pullulan production by Aureobasidium pullulans in batch culture using olive oil and sucrose as carbon sources

The production of pigment-free pullulan by Aureobasidium pullulans, using o live oil and sucrose as carbon (C) sources, in shake flasks, was investigat ed. Optimum medium composition for pullulan elaboration was 80 g/L sucrose, 25 mL/L olive oil, 5 mL/L Tween-80, 10 g/L glutamic acid, and an initial p H of 5.5. Maximum pullulan concentration (51.5 g/L), productivity (8.6 g/L. d), and yield (80.3%)were achieved under these conditions after 120 h of fe rmentation. The principal advantage of using olive oil and sucrose simultan eously as C sources was the elimination of the inhibitory effect of high su crose concentrations (>60 g/L) on pullulan production by the microorganism, Structural characterization by C-13-NMR, monosaccharide, and methylation a nalyses, and pullulanase digestion, combined with size-exclusion chromatogr aphy, confirmed the identity of pullulan and the homogeneity of the release d polysaccharide in the fermentation broths. There were no significant diff erences in structure between pullulan samples isolated from either olive oi l-supplemented media or olive oil-free media. The molecular size of pullula n from the combined olive oil-sucrose fermentation was slightly lower (1.1 x 10(6)) than that of conventional fermentation with sucrose as a single C source (1.4 x 10(6)). Lowering the initial pH of the medium resulted in inc reased molecular size for the released polymer, but a lower pullulan yield.