Victoria E. Santos

Xanthan gum: production, recovery, and properties

Xanthan gum is a microbial polysaccharide of great commercial significance. This review focuses on various aspects of xanthan production, including the producing organism Xanthomonas campestris, the kinetics of growth and production, the downstream recovery of the polysaccharide, and the solution properties of xanthan.

Oxygen transfer and uptake rates during xanthan gum production

Oxygen uptake rate and oxygen mass transfer rate have been studied during xanthan gum production process in stirred tank bioreactor. Empirical equations for the oxygen mass transfer coefficient have been obtained taking into account several variables such as air flow rate, stirrer speed and apparent viscosity. Oxygen uptake rate evolution in the course fermentation has been measured, obtaining an equation as a function of biomass concentration, including overall growth and non growth-associated oxygen uptake. A metabolic kinetic model has been employed for xanthan gum production description including oxygen mass transfer and uptake rates. The results point out that this model is able to describe adequately not only oxygen dissolved evolution, but also of the production of xanthan and substrate consumption. Also, the influence of several parameters (k(L)a, air flow rate and dissolved oxygen) in the evolution of the key compounds of the system have been studied. The results of the simulation shown that an increasing of dissolved oxygen concentration favor the xanthan gum production.

Xanthan gum production under several operational conditions: molecular structure and rheological properties☆☆

Xanthan gum production under several operational conditions has been studied. Temperature, initial nitrogen concentration and oxygen mass transfer rate have been changed and average molecular weight, pyruvilation and acetylation degree of xanthan produced have been measured in order to know the influence of these variables on the synthesised xanthan molecular structure. Also, xanthan gum solution viscosity has been measured, and rheological properties of the solutions have been related to molecular structure and operational conditions. The Casson model has been employed to describe the rheological behaviour. The parameter values of the Casson model, tau(0) and K(c), have been obtained for each polysaccharide synthesised under different operational conditions. Both pyruvilation and acetylation degrees and average molecular weight of xanthan increase with fermentation time at any operating conditions. Xanthan molecules with the highest average molecular weight have been obtained at 25 degrees C. Nevertheless, at this temperature acetate and pyruvate radical concentration are lowest. Nitrogen concentration in broth does not show any clear influence over xanthan average molecular weight, although with high nitrogen source concentration xanthan with low pyruvilation degree is produced.

Nutritional study of Xanthomonas campestris in xanthan gum production by factorial design of experiments

A nutritional study of Xanthomonas campestris in the production of xanthan gum was carried out by factorial design and analysis of experiments. The concentrations of nutrients such as nitrogen, phosphorus, magnesium, and sulfur were studied by means of a factorial design at two levels, reduced to a half with four central points for error estimation. Three responses were considered, corresponding to biomass, sucrose, and xanthan concentrations, at four different times: 12, 16, 20, and 24 h. The influence of nitrogen, phosphorus, and magnesium on the biomass, and the influence of nitrogen, phosphorus, and sulfur on xanthan production, were significant, although any variable influenced sucrose consumption. An optimized medium was proposed for xanthan production.

Kinetic model for anaerobic digestion of livestock manure

Two unstructured segregated kinetic models to describe the anaerobic digestion of livestock manure are developed and experimental batch data obtained from beef cattle in a 2.0-l work volume digestor fitted to both proposed kinetic models to obtain the values of the parameters. The results obtained by fitting show that the second model proposed has both statistical and physical meaning in the parameter values obtained. The model takes into account a simplified reaction scheme formed by six reactions. Several simplifications have been made (lumping, pseudo-steady state for one compound, first order kinetics, etc.) yielding four key compounds to be analysed and fitted to the model as production-rates expressions (total biomass, chemical oxygen demand (COD), volatile acids, and methane). The model considers three main stages in the process: enzymatic hydrolysis of the waste, growth of ‘acetogenic’ microorganisms (production of acids nongrowth associated), and growth of ‘methanogenic’ microorganisms associated with methane production; the two last processes are accompanied by substrate consumption for maintenance. A non-linear multiple-response regression technique coupled to a fourth-order Runge‐Kutta algorithm has been employed to obtain the values of the ten parameters. The model is able to reproduce the experimental data obtained for beef manure anaerobic digestion with more accuracy than experimental error.

Xanthan gum production: An unstructured kinetic model

Xanthan production was studied in a stirred-tank fementor and modeled using unstructured kinetic models. First, the influences of the operational conditions have been studied. Temperature (between 22 and 34°C), aeration (changing stirrer speed between 150 and 1,000 rpm, maintained at constant or varied through fermentation time), and the pH control (with two alkalis) were analyzed. Then, unstructured kinetic models proposed in the literature for this system were reviewed and applied. These models have been checked to describe the experimental results, calculating the parameters by nonlinear regression. The results show that these models do not take into account all the necessary nutrients, which are carbon source, nitrogen source, and dissolved oxygen. Afterward, an unstructured kinetic model describing biomass, carbon source, nitrogen source, and dissolved oxygen evolutions was proposed and applied. Parameters estimation were carried out by means of both differential and integral methods. Parameters values were finally obtained applying an integral method using non-linear regression techniques. The model proposed in this work is composed of five differential equations with production rates of the five components taken into account: biomass, carbon, and nitrogen sources, xanthan, and dissolved oxygen, capable of fitting all the three experiments considered, at different temperatures and controlling and not controlling pH.

Metabolic structured kinetic model for xanthan production

Abstract A metabolic structured kinetic model for xanthan gum production is described and fitted to experimental data obtained in a batch stirred tank reactor. The model is able to describe the evolution of biomass, consumption of carbon, nitrogen, dissolved oxygen, and production of xanthan at different temperatures. The description of growth is carried out by means of an unstructured model taking the nitrogen source as the limiting nutrient, employing the logistic equation which fits adequately the experimental data of the increase in biomass concentration as a function of initial concentrations of biomass and nitrogen source. The model proposed is metabolically structured because it takes into account the carbon source metabolism into the cell, describing xanthan production, carbon source, and dissolved oxygen consumption in a structured way according to a reaction network as a simplified scheme of the intracellular metabolism. The limiting nutrient of xanthan production and carbon source consumption is supposed to be dissolved oxygen. The parameter estimation has been performed by fitting to experimental data, employing an integral method coupling a fourth-order Runge-Kutta algorithm to a multiple-response nonlinear regression technique. Runs performed at four different temperatures (25, 28, 31, and 34°C) are fitted and described by the model.

Analysis of Dibenzothiophene Desulfurization in a Recombinant Pseudomonas putida Strain

ABSTRACT Biodesulfurization was monitored in a recombinant Pseudomonas putida CECT5279 strain. DszB desulfinase activity reached a sharp maximum at the early exponential phase, but it rapidly decreased at later growth phases. A model two-step resting-cell process combining sequentially P. putida cells from the late and early exponential growth phases was designed to significantly increase biodesulfurization.

1,3-Propanediol production from glycerol with a novel biocatalyst Shimwellia blattae ATCC 33430: Operational conditions and kinetics in batch cultivations

Shimwellia blattae ATCC 33430 as biocatalyst in the conversion of 1,3-propanediol from glycerol is herein evaluated. Several operational conditions in batch cultivations, employing pure and raw glycerol as sole carbon source, were studied. Temperature was studied at shaken bottle scale, while pH control strategy, together with the influence of raw glycerol and its impurities during fermentation were studied employing a 2L STBR. Thereafter, fluid dynamic conditions were considered by changing the stirring speed and the gas supply (air or nitrogen) in the same scale-up experiments. The best results were obtained at a temperature of 37°C, an agitation rate of 200rpm, with free pH evolution from 6.9 and subsequent control at 6.5 and no gas supply during the fermentation, employing an initial concentration of 30g/L of raw glycerol. Under these conditions, the biocatalyst is competitive, leading to results in line with other previous works in the literature in batch conditions, reaching a final concentration of 1,3-propanediol of 13.84g/L, with a yield of 0.45g/g and a productivity of 1.19g/(Lh) from raw glycerol.

1,3-Propanediol production by Klebsiella oxytoca NRRL-B199 from glycerol. Medium composition and operational conditions

Highlights • 1,3-Propanediol is produced from glycerol using Klebsiella oxytoca NRRL-B199.• The medium composition was optimized by an orthogonal experimental design.• Scale-up form shaken bottles to STBR was studied.• Operating conditions, agitation and temperature, were optimized.• Under these conditions, 13.5 g/L of propanediol (selectivity = 86% with respect to glycerol) can be obtained.