Almudena Alcon

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.

Simulation of xanthan gum production by a chemically structured kinetic model

A chemically structured kinetic model for xanthan production is proposed. Both carbon and nitrogen source metabolisms into cells are taken into account by the model. A kinetic reaction network is proposed, using lumping of several compounds into groups for a simplification of the metabolic pathways. Seven reactions are taken into account in the simplified reaction network, involving 11 different species; kinetic equations of Monod type for the reactions involved in the network considered are assumed. A stoichiometric study yields seven key components, the kinetic model is formulated as a set of differential equations formed by the production rates of the seven key components (six equations only if the pseudo-steady state is assumed for ATP), while the evolution of the other components involved in the reaction network are derived. Simulations of different cases in a stirrer tank bioreactor have been made, using a linear increase of stirrer speed, at different dissolved oxygen concentrations and with several initial nitrogen concentrations. The model is able to simulate the system evolution under different operational conditions, predicting an optimum value for the initial nitrogen concentration.

Desulfurization of dibenzothiophene using the 4S enzymatic route: Influence of operational conditions on initial reaction rates

The influence of operational conditions (pH, temperature and oxygen transfer rate) on the initial reaction rates of the four reactions involved in the 4S biodesulfurization route of dibenzothiophenes (DBT) has been studied. The bioprocess was carried out using a genetically modified organism, Pseudomonas putida CECT 5279. The rates of the four reactions were calculated from the rates of production of different compounds involved in the 4S pathway, by matrix manipulation. The initial (zero time) reaction rates showed a slight dependence on oxygen transfer rate. Temperature and pH were optimal at 30°C and 9, respectively, temperature being the most important variable. This study also identifies the last reaction as the limiting step in the pathway.