Statistical optimization of pullulan production from Asian palm kernel and evaluation of its properties

Pullulan, a biodegradable exopolysaccharide, was produced from Asian Palmyra palm kernel by solid-state fermentation. Levels of medium variables, namely carbon to nitrogen ratio (C/N), pH, NaCl concentration and ZnSO4·5H2O concentration were optimized to maximize pullulan production using Box-Behnken design of experiments. Optimal values were predicted as: C/N ratio - 28.1, pH - 6.6, NaCl - 0.78 g/l and ZnSO4·5H2O - 0.37 g/l. Theoretical pullulan yield predicted under optimum condition was 30.4 mg/gds. Pullulan was produced under optimum condition and an experimental yield of 28.7 ± 0.3 mg/gds was obtained. 13C NMR spectra of the exopolysaccharide produced from Asian palm kernel revealed the presence of anomeric α (1→6) linked maltosyl units. The weight-average molecular weight of the polymer was determined to be 8.4 × 106 Da by gel permeation chromatography. Thermal decomposition temperature of pullulan was obtained to be 245 °C. The tensile strength of pullulan film (0.5 mm thick) was found to be 27 MPa.