Evaluation of Some Agro-Industrial Wastes as Fermentation Medium for Pullulan Production by Aureobasidium pullulans AZ-6

Genetic algorithm-optimized artificial neural network for multi-objective optimization of biomass and exopolysaccharide production by Haloferax mediterranei

Microbial production of industrially important exopolysaccharide (EPS) from extremophiles has several advantages. In this study, key media components (i.e., sucrose, yeast extract, and urea) were optimized for biomass growth and extracellular EPS production in Haloferax mediterranei DSM 1411 using Box-Behnken design. In a multi-objective optimization framework, response surface methodology (RSM) and genetic algorithm (GA)-optimized artificial neural network (ANN) were used to minimize biomass growth while increasing EPS production. The performance of the selected ANN model for the prediction of biomass and EPS (R2: 0.964 and 0.975, respectively) was found to be better than that of the multiple regression model (R2: 0.818, 0.963, respectively). The main effect of sucrose and its interaction with urea appears to have a significant effect on both responses. The ANN model projects an increase in EPS production from 4.49 to 18.2 g l-1 while shifting the priority from biomass to biopolymer. The optimized condition predicted a maximum biomass and EPS production of 17.27 g l-1 and 17.80 g l-1, respectively, at concentrations of sucrose (19.98 g l-1), yeast extract (1.97 g l-1), and urea (1.99 g l-1). Based on multi-objective optimization, the GA-ANN model predicted an increase in the EPS to biomass ratio for increasing the EPS and associated biomass production. The extracted EPS, identified as Gellan gum through NMR spectroscopy, was further characterized for surface and elemental composition using SEM-EDX analysis.

Production and applications of pullulan from lignocellulosic biomass: Challenges and perspectives

Pullulan is an exopolysaccharide produced by Aureobasidium pullulans, with interesting characteristics which lead to its application in industries such as pharmaceuticals, cosmetics, food, and others. To reduce production costs for industrial applications, cheaper raw materials such as lignocellulosic biomass can be utilized as a carbon and nutrient source for the microbial process. In this study, a comprehensive and critical review was conducted, encompassing the pullulan production process and the key influential variables. The main properties of the biopolymer were presented, and different applications were discussed. Subsequently, the utilization of lignocellulosics for pullulan production within the framework of a biorefinery concept was explored, considering the main published works that deal with materials such as sugarcane bagasse, rice husk, corn straw, and corn cob. Next, the main challenges and future prospects in this research area were highlighted, indicating the key strategies to favor the industrial production of pullulan from lignocellulosic biomasses.

Exopolysaccharides of Fungal Origin: Properties and Pharmaceutical Applications

Fungal exopolysaccharides (EPSs) represent an important group of bioactive compounds secreted by fungi. These biopolymers can be utilized individually or in combination with different bioactive substances for a broad range of pharmaceutical field applications, due to their various biological activities, such as antioxidant, antimicrobial, anti-inflammatory, antiviral, anti-diabetic, and anticoagulant effects. The paper presents an up-to-date review of the main fungal polysaccharides (pullulan, schizophyllan, scleroglucan, botryosphaeran, lentinan, grifolan, and lasiodiplodan), highlighting their structures, producing strains, and useful properties in a double position, as controlled release (rate and selectively targeting) drug carriers, but mostly as active immunomodulating and antitumor compounds in cancer therapy.

Optimization of hazelnut husk medium for pullulan production by a domestic A. pullulans strain

Hazelnut husk is one of the most abundant agricultural residue in Turkey. Valorization of this lignocellulosic biomass would provide a promoting alternative for economical production of pullulan. In this study, dried hazelnut husk hydrolysate was used directly as fermentation medium for pullulan production by a domestic strain of Aureobasidium pullulans. The aim of this work was the optimization of some fermentation medium parameters by central composite design using response surface methodology (RSM). The effects of (NH₄)₂SO₄ concentration, the volume of concentrated H₂SO₄ and the amount of ground hazelnut husk on pullulan production were optimized by RSM. The optimum levels of the fermentation parameters defined as 7.2 gL^-1, 2.5 mL and 20 g, respectively. The maximum pullulan and exopolysaccharide concentrations were determined as 74.39 and 75.95 gL^-1_, respectively in the optimum conditions. Specific growth rate of the strain was found as 0.097 h^-1. FTIR spectral attributes confirmed the structure of pullulan. Thermal decomposition temperature of synthesized pullulan was found as 247.15 °C. This study showed that hazelnut husk was one of the novel substrate for production of the pullulan by A. pullulans AZ-6. No previous work was found to utilize dried hazelnut husk as fermentation medium for pullulan production by A. pullulans.

Sustainable Exopolysaccharide Production by Rhizobium viscosum CECT908 Using Corn Steep Liquor and Sugarcane Molasses as Sole Substrates

Microbial exopolysaccharides (EPS) are promising alternatives to synthetic polymers in a variety of applications. Their high production costs, however, limit their use despite their outstanding properties. The use of low-cost substrates such as agro-industrial wastes in their production, can help to boost their market competitiveness. In this work, an alternative low-cost culture medium (CSLM) was developed for EPS production by Rhizobium viscosum CECT908, containing sugarcane molasses (60 g/L) and corn steep liquor (10 mL/L) as sole ingredients. This medium allowed the production of 6.1 ± 0.2 g EPS/L, twice the amount produced in the standard medium (Syn), whose main ingredients were glucose and yeast extract. This is the first report of EPS production by R. viscosum using agro-industrial residues as sole substrates. EPS_CSLM and EPS_Syn exhibited a similar carbohydrate composition, mainly 4-linked galactose, glucose and mannuronic acid. Although both EPS showed a good fit to the Herschel-Bulkley model, EPS_CSLM displayed a higher yield stress and flow consistency index when compared with EPS_Syn, due to its higher apparent viscosity. EPS_CSLM demonstrated its potential use in Microbial Enhanced Oil Recovery by enabling the recovery of nearly 50% of the trapped oil in sand-pack column experiments using a heavy crude oil.

Coproduction of exopolysaccharide and polyhydroxyalkanoates from Sphingobium yanoikuyae BBL01 using biochar pretreated plant biomass hydrolysate

Sphingobium yanoikuyae BBL01 can produce exopolysaccharides (EPS) and polyhydroxyalkanoates (PHAs). The effect of side products (furfural, hydroxymethylfurfural (HMF), vanillin, and acetate) produced during pretreatment of biomass was evaluated on S. yanoikuyae BBL01. It was observed that a certain concentration range (0.01-0.03 %) of these compounds can improve growth, EPS production, and polyhydroxybutyrate (PHB) accumulation. The addition of HMF increases glucose and xylose utilization while other side products have a negative effect. The C/N of 5 favors EPS production (3.24 ± 0.05 g/L), while a higher C/N ratio of 30 promotes PHB accumulation (38.7 ± 0.08 % w/w), when commercial sugar is used as a carbon source. Pine biomass-derived biochar was able to remove 40 ± 2.1 % of total phenolic. Various biomass hydrolysates were evaluated and the use of detoxified pine biomass hydrolysate (DPH) as a carbon source resulted in the higher coproduction of EPS (2.83 ± 0.03 g/L) and PHB (40.8 ± 2.4 % w/w).