PULLULAN CONTENT OF THE ETHANOL PRECIPITATE FROM FERMENTED AGROINDUSTRIAL WASTES

Ethanol-precipitated substances after fermentation of various agro-ind ustrial wastes by Aureobasidium pullulans were examined for their pull ulan content. Grape skin pulp extract, starch waste, olive oil waste e ffluents and molasses served as substrates for the fermentation. A glu cose-based defined medium was used for comparison purposes. Samples we re analysed by an enzyme-coupled assay method and by high-performance anion-exchange chromatography with pulsed amperometric detection after enzymic hydrolysis with pullulanase. Fermentation of grape skin pulp extract gave 22.3 g l(-1) ethanol precipitate, which was relatively pu re pullulan (97.4% w/w) as assessed by the coupled-enzyme assay. Hydro lysed starch gave only 12.9 g l(-1) ethanol precipitate, which increas ed to 30.8 g l(-1) when the medium was supplemented with NH4NO3 and K2 HPO4; this again was relatively pure pullulan (88.6% w/w). Molasses an d olive oil wastes produced heterogeneous ethanol-precipitated substan ces containing small amounts of pullulan, even when supplemented with nitrogen and phosphate. Overall, grape skin pulp should be considered as the best substrate for pullulan production. Starch waste requires s everal hydrolyis steps to provide a usable carbon source, which reduce s its economic attraction as an industrial process.