Pullulan Production Using Molasses and Corn Steep Liquor as Agro-industrial Wastes: Physiochemical, Thermal and Rheological Properties

Background and Objective: Pullulan is a microbial exopolysaccharide with wide uses in various industries. The aim of this study was to investigate pullulan production from agro-industrial wastes and study of pH, molasses concentration and corn steep liquor concentration as independent variables and yield of pullulan as response. Material and Methods: Briefly, 5% (v v^-1) of the inoculation media (yeast extract 3 g, malt extract 3 g, peptone 5 g and sucrose 10 g per liter of distilled water), including Aureobasidium pullulans were added into media, containing 100 ml of molasses (100, 150 and 200 g l^-1) and various corn steep liquor concentrations (20, 40 and 60 ml l^-1) at adjusted pH (4.5, 5.5 and 6.5). After extraction and separation of the biomass using centrifuge, two folds of the supernatant volume of cold ethanol were added to the samples and stored at 4 °C for 24 h. After centrifuging, pullulan was dried and analyzed using Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and rheological tests. Results and Conclusion: Findings revealed that the maximum production yield (18.29 g l- 1 ±0.10) was achieved under optimum fermentation conditions (pH of 5.3, molasses concen-tration of 165 g l^-1 and corn steep liquor concentration of 43 ml l^-1). Then, physiochemical and thermal properties of the pullulan under the highlighted conditions were investigated. Pullulan included 78.8% solubility with no hygroscopicity. Furthermore, structural analysis using Fou-rier transform infrared and X-ray diffraction verified presence of pullulan with an amorphous structure in the supernatant. The exopolysaccharide included acceptable thermal stability and gel-like behavior; in which, the elastic component was predominant based on the results of thermogravimetric analysis and rheological properties, respectively.