Characterization of pullulan produced from beet molasses by Aureobasidium pullulans in a stirred tank reactor under varying agitation

• Published in: Enzyme and microbial technology 2002-07, Vol.31 (1), p.122-132
• Main Authors: Lazaridou, A, Roukas, T, Biliaderis, C.G, Vaikousi, H
• Format: Article
• Language: English
• Subjects: [formula omitted] NMR spectroscopy; Aureobasidium pullulans; Beet molasses; Biological and medical sciences; Biotechnology; Exopolysaccharide; Fermentation; Fundamental and applied biological sciences. Psychology; Light scattering; Methods. Procedures. Technologies; Microbial engineering. Fermentation and microbial culture technology; Molecular weight; Pullulan; Pullulanase; Viscosity
• ISSN: 0141-0229; 1879-0909
• DOI: 10.1016/S0141-0229(02)00082-0

The molecular characteristics of pullulan produced from beet molasses, following their pretreatment with sulfuric acid and activated carbon, by Aureobasidium pullulans P56 (a melanin-deficient strain) in a stirred tank fermentor under varying agitation conditions have been examined. A maximum pullulan concentration of 49 g l −1, biomass dry weight of 25 g l −1, pullulan yield of 50% and sugar utilization of 97% were achieved at an initial sugar concentration in the medium of 100 g l −1 and impeller speed of 700 rpm; under these conditions the pO 2 levels in the bioreactor were maintained at low levels of dissolved O 2 saturation (∼7%). Structural characterization of the isolated polysaccharides from the fermentation broths by 13 C NMR spectroscopy and pullulanase digestion combined with size exclusion chromatography confirmed the identity of pullulan and the homogeneity (>94% d.b.) of the elaborated polysaccharides by the microorganism. The exopolysaccharide preparations were also free of contaminating proteins. Using multiangle laser light scattering (MALLS) and refractive index (RI) detectors, in conjunction with high-performance size-exclusion chromatography (HPSEC), molecular size distributions and estimates of the molecular weight ( M w=5.3–14.7×10 4), root-mean square of the radius of gyration ( R g=24–33 nm) and polydispersity index ( M w/ M n=1.7–2.6) were obtained. In most culture systems examined there was a reduction in the molecular size of the isolated polysaccharides as time of fermentation progressed. In the concentration range of 2.8–9.5% (w/v), the solution rheological behavior of the isolated pullulans was almost Newtonian (within 1 and 1200 s −1 at 20 °C). Overall, beet molasses were proven as an attractive fermentation medium for the production of pullulan by A. pullulans.