EVALUATION OF CAROB POD AS A SUBSTRATE FOR PULLULAN PRODUCTION BY AUREOBASIDIUM-PULLULANS

The production of extracellular polysaccharides from carob pod extract by Aureobasidium pullulans in batch fermentation was investigated. Optimum conditions for polysaccharide productivity, polysaccharide yield, and fermentation efficiency were: initial sugar concentration of 25 g/L, initial pH 6.5, and temperature 25-30 degrees C. A maximum polysaccharide concentration (6.5 g/L), polysaccharide productivity (2.16 g/L/d), total biomass concentration (6.3 g/L), and polysaccharide yield (30%) were obtained with inoculum at 10% (v/v), initial sugars in carob pod extract of 25 g/L, pH 6.5, and 25 degrees C. The highest values of pullulan proportion (70% of total polysaccharides) and fermentation efficiency (89%) were assumed at initial sugar concentration of 25 g/L, pH 6.5 and 30 degrees C. Structural characterization of purified pullulan samples by monosaccharide and methylation analyses, C-13-NMR, and pullulanase digestion combined with size-exclusion chromatography revealed the presence of mainly alpha-(1 --> 4) (68%) and alpha-(1 --> 6) (31%) glucosidic linkages; however, small amounts (<1%) of triply linked (1, 3, 4- and 1, 4, 6-Glc) glucose residues were detected. The molecular-size distribution and intrinsic viscosity of pullulan derived from culture grown at pH 4.5 (30 degrees C) showed a higher molecular weight than its counterpart obtained at pH 6.5 (30 degrees C).