Batch Fermentation Kinetics of Pullulan from Aureobasidium pullulans Using Low Cost Substrates

Advances in fermentative production, purification, characterization and applications of gellan gum

Multiple microbial exopolysaccharides have been reported in recent decade with their structural and functional features. Gellan gum (GG) is among these emerging biopolymers with versatile properties. Low production yield, high downstream cost, and abundant market demand have made GG a high cost material. Hence, an understanding on the various possibilities to develop cost-effective gellan gum bioprocess is desirable. This review focuses on details of upstream and downstream process of GG from an industrial perspective. It emphasizes on GG producing Sphingomonas spp., updates on biosynthesis, strain and media engineering, kinetic modeling, bioreactor design and scale-up considerations. Details of the downstream operations with possible modifications to make it cost-effective and environmentally sustainable have been discussed. The updated regulatory criteria for GG as a food ingredient and analytical tools required to validate the same have been briefly discussed. Derivatives of GG and their applications in various industrial segments have also been highlighted.

Pullulan production from synthetic medium by a new mutant of Aureobasidium pullulans

Pullulan with different molecular-weight could be applied in various fields. A UV-induced mutagenesis Aureobasidium pullulans UVMU6-1 was obtained from the strain A. pullulans CGMCC3.933 for the production of low-molecular-weight pullulan. First, the obtained polysaccharide from A. pullulans UVMU6-1 was purified and identified to be pullulan with thin-layer chromatography, Fourier transform infrared, and nuclear magnetic resonance. Then, culture medium and conditions for this strain were optimized by flask fermentation. Based on the optimized medium and culture conditions (pH 4, addition of 4 g/L Tween 80 for 96 hr of cultivation), continuously fermentation was performed. The highest pullulan production and dry biomass was 109 and 125 g/L after fermentation for 114 hr, respectively. The average productivity was about 1 g/L/hr, which was intensively higher than the previous reported. This study would lay foundations for the industrial production of pullulan.

Statistical optimization for enhanced yields of probiotic Bacillus coagulans and its phage resistant mutants followed by kinetic modelling of the process

Probiotics are microorganisms which when administered in adequate amounts confer health benefits to the host. A leading pharmaceutical company producing Bacillus coagulans as a probiotic was facing the problem of recurring phage attacks. Two mutants viz. B. co PIII and B. co MIII that were isolated as phage resistant mutants after UV irradiation and MMS treatment of phage sensitive B. coagulans parental culture were characterized at functional and molecular level and were noted to have undergone interesting genetic changes. The non-specific genetic alterations induced by mutagenesis can also lead to alterations in cell performance. Hence, in the current study the parental strain and the two mutants were selected for shake flask optimization. Plackett–Burman design was used to select the significant culture variables affecting biomass production. Evolutionary operation method was applied for further optimization. The study showed wide variations in the nutritional requirements of phage resistant mutants, post exposure to mutagens. An increment of 150, 134 and 152 % was observed in the biomass productions of B. coagulans (parental type) and mutants B.co PIII and B.co MIII respectively, compared to the yield from one-factor-at-a-time technique. Using Logistic and modified Leudeking–Piret equations, biomass accumulation and substrate utilization efficiency of the bioprocess were determined. The experimental data was in agreement with the results predicted by statistical analysis and modelling. The developed model may be useful for controlling the growth and substrate consumption kinetics in large scale fermentation using B. coagulans.

An indigenous hyperproductive species of Aureobasidium pullulans RYLF-10: influence of fermentation conditions on exopolysaccharide (EPS) production

In recent years, a significant interest has been generated in discovering and developing exopolysaccharides (EPS) produced by microorganisms, especially fungi due to their multifaceted industrial and pharmacological applications. A number of filamentous and cellular fungi have been explored for this; however, according to the existing literature, the work on exopolysaccharide production by indigenous culture on this aspect is still very less and requires a serious attention. The present work is an attempt in this regard and aims to optimize the submerged culture conditions to produce the exopolysaccharides from an indigenous yeast Aureobasidium pullulans RYLF-10 with respect to several operating parameters in shake flask fermentation. The yeast A. pullulans RYLF-10 was identified by 18s RNA sequencing and detailed study on its nutritional requirements, and environmental conditions for submerged culture have been optimized. The optimal temperature and pH for both the vegetative growth and EPS production were found to be 28 ± 1 °C and 5.0, respectively, while the agitation speed and inoculum size were reported to be 150 rpm and 1 % (v/v), respectively. Sucrose (50 g/l) and yeast extract (1 g/l) were found to be the most suitable carbon and nitrogen sources which worked best in the ratio of 60:1 and resulted in the maximum EPS yield. Similarly, the other variables like growth regulator (riboflavin) and minerals (NaCl + K2HPO4 + MgSO4) altogether resulted in a noteworthy EPS yield of 45.24 g/l which is the maximum yield from this indigenous isolate of A. pullulans RYLF-10.

Evaluation of medium composition and fermentation parameters on pullulan production by Aureobasidium pullulans

The goal of this study was to enhance pullulan production by evaluating the effects of different fermentation parameters. Various carbon sources and their concentrations, yeast extract (YE) concentrations, fermentation temperatures and various pH profiles were examined. The optimal growth condition for pullulan production by Aureobasidium pullulans has been found as 75 g/L of sucrose as carbon source, 3 g/L of YE and cultivation temperature at 30 (°)C. Under these conditions with an initial pH at 5, 20.7 g/L of final pullulan concentration and 0.22 g/L/h maximum production rate were obtained. Later on, various pH profiles, agitation speeds, aerations and fed-batch fermentation were evaluated. The results demonstrated that pullulan production was enhanced to 25.8 g/L after 7-day cultivation with a 0.68 -g/L/h maximum production rate. There was no significant improvement of pullulan production from fed-batch fermentation. The optimal kinetics parameters were as follows: initial pH at 2.0, switched to pH 5.0 after 72 h and kept constant; agitation speed at 200 rpm; aeration at 1.5 vvm. The quality analysis demonstrated that the pullulan content produced from optimal conditions was 94.5% and its viscosity was 2.3 centipoise (cP). Fourier transform infrared spectroscopy also suggested that pullulan dominated the produced exopolysaccharide.