Optimization of High Molecular Weight Pullulan Production by Aureobasidium pullulans in Batch Fermentations

Abstract

Of five strains of Aureobasidium pullulans studied, NRRL Y-2311-1 yielded the highest titer (26.2 g/L) of pullulan and formed the lowest amount of melanin-like pigment. Sucrose was superior to glucose as the carbon and energy source on the basis of yield and titer of pullulan produced. Pullulan titer was higher (26.2 vs 5.1 g/L), biomass concentration was lower (6.9 vs 12.7 g/L), and DO was lower (0 vs 60% of saturation) when the fermenter was agitated by a marine propeller compared to Rushton impellers. Pullulan produced by strain NRRL Y-2311-1 ranged in weight-average molar mass (M(w)) from 486 KDa and number-average molar mass (M(n)) from 220 Da on day 1 of growth to 390 KDa and 690 Da on day 6; M(w) declined by about 35% from day 1 to day 3, the day of maximum pullulan titer. For the other strains, the ranges of molar mass on the day of maximum pullulan titer were 338-614 KDa (M(w)) and 100-6820 Da (M(n)).

Adhesion of Aureobasidium pullulans Is Controlled by Uronic Acid Based Polymers and Pullulan

“…To culture pullulan, fermentors are often run for long periods of time to maximize pullulan production, on the order of several days. 9 For the hour 3 cells in our study, we have very little exopolymer, and due to the size (39.5 nm) and chemical information, it is apparently entirely uronic acid based. The size of this polymer is sufficient to cause steric repulsion between the fungal macromolecules and the AFM tip, but this repulsion does not prevent the cells from adhering strongly to silicon nitride or from attaching to quartz media.…”

“…A. pullulans strain NRRL Y-2331-1, which produces high yields of a nonpigmented form of pullulan, 9 was obtained from the United States Department of Agriculture (USDA). The growth media consisted of a complex nitrogen stock solution with sucrose as the carbon source, 5 containing (per 1 L of ultrapure water): 2.0 g of yeast extract, 0.5 g of (NH 4 ) 2 SO 4 , 1.0 g of NaCl, 0.2 g of MgSO 4 , 3.0 g of K 2 HPO 4 , 0.01 g of FeSO 4 , 0.01 g of MnSO 4 , 0.01 g of ZnSO 4 , and 50 g of sucrose.…”

Enhanced production of pullulan by two strains of A. pullulans with different concentrations of soybean oil in sucrose solution in batch fermentations

“…Different strains of A. pullulans produce substantially different titers and yields (on sugar substrates) of pullulan (Campbell et al, 2004;Gibson and Coughlin, 2002;West and Strohfus, 2001). Compared to the other strain, the NRRL Y-2311-1 produced a higher yield of unpigmented and reasonably higher molecular weight pullulan when cultivated under the conditions reported herein.…”

“…Some authors have reported optimum results when oil was added frequently during fermentation as a sole carbon source (Gibson and Coughlin, 2002;Jones and Porter, 1998;Ohta et al, 1995).…”

“…To avoid the black pigment formed by some strains, the strains NRRL Y-2311-1 and NRRL Y-6220 were used; according to Gibson and Coughlin (2002) and Badr-Eldin et al (1994), both produce the pigment-free pullulan and the highest yields. The process was also studied by the timing yield in hours to quantify the overall sucrose consumption for evaluation of the highest production, due to the self-consumption of the cells during the process in the absence of substrate.…”