Nestrukturirani modeli mliječno-kiselog vrenja

To describe a microbial process, two kinds of models can be developed, structured and unstructured models. Contrary to structured models, which take into account some basic aspects of cell structure, their function and composition, no physiological characterization of cells is considered in unstructured models, which only consider total cellular concentration. However, in spite of their simplicity, unstructured models have proven to accurately describe lactic acid fermentation in a wide range of experimental conditions and media. A partial link between cell growth and production, namely the Luedeking and Piret model, is mostly considered by the authors. Culture pH is the main parameter to be considered for model development. Acidic pH leads to inhibitory concentrations of undissociated lactic acid, the main inhibitory component, which causes cessation of growth and then production. On the other hand, pH control at optimal value for LAB growth allows to overcome product inhibition (by the total lactic acid produced or its undissociated part); hence nutritional limitations have to be considered for model development. Nitrogen is mainly involved in cessation of growth, owing to the fastidious nutritional requirements of LAB, while lactic acid production ceased when carbon was exhausted from the medium. The lack of substrate inhibition when usual concentrations of carbon substrate are used should be noted.Da bi se opisao mikrobni proces, upotijebljeni su strukturirani i nestrukturirani modeli. Strukturirani modeli uzimaju u obzir strukturu, funkciju i raspored stanica, a nestrukturirani ne uzimaju fiziološka svojstva, već samo ukupnu koncentraciju stanica. Ipak, usprkos njihovoj jednostavnosti, nestrukturirani modeli precizno opisuju mliječno-kiselo vrenje u različitim eksperimentalnim uvjetima i na raznim podlogama. Autori najčešće koriste Luedekingov i Piretov model, koji opisuje djelomičnu vezu između rasta stanica i proizvodnje mliječne kiseline. U razvoju ovoga modela najčešće je pH-vrijednost glavni parametar. Pri niskoj pH-vrijednosti nastaju inhibicijske koncentracije nedisocirane mliječne kiseline, što zaustavlja rast mliječno-kiselih bakterija, a time i proizvodnju mliječne kiseline. Taj se inhibicijski učinak može prevladati održavanjem optimalne pH-vrijednosti, ali pritom treba uzeti u obzir utjecaj hranjivih tvari na rast mliječno-kiselih bakterija. Nedostatak dušika je najčešći uzrok inhibicije mliječno-kiselih bakterija, jer im je prijeko potreban za rast, dok nakon iscrpljivanja ugljika iz podloge prestaje proizvodnja mliječne kiseline, što se može izbjeći korištenjem odgovarajućih koncentracija ugljika

Improved growth model for two-stage continuous cultures of Lactobacillus helveticus

An unstructured model for growth and lactic acid production during two-stage continuous cultures of Lactobacillus helveticus was previously developed. The Verlhust model was considered to describe growth kinetics. Production models was based on modified Luedeking-Piret expressions involving an inhibitory effect for the first stage (seed culture) and a nutritional limitation effect for the second stage (culture). To account for the decrease of the biomass concentration observed in the second stage, the dilution rate Dc was replaced by an exponential term of the dilution rate \u3b1 exp (Dc/\u3b2 ) in the growth and product relations. Contrarily to the previous model, the important decrease of the biomass concentration observed at steady state in the second stage at high dilution rates, namely close to wash out, was correctly described by the new model. It also proved to satisfactory describes production data and volumetric productivity

Unstructured Models for Lactic Acid Fermentation – A Review

To describe a microbial process, two kinds of models can be developed, structured and unstructured models. Contrary to structured models, which take into account some basic aspects of cell structure, their function and composition, no physiological characterization of cells is considered in unstructured models, which only consider total cellular concentration. However, in spite of their simplicity, unstructured models have proven to accurately describe lactic acid fermentation in a wide range of experimental conditions and media. A partial link between cell growth and production, namely the Luedeking and Piret model, is mostly considered by the authors. Culture pH is the main parameter to be considered for model development. Acidic pH leads to inhibitory concentrations of undissociated lactic acid, the main inhibitory component, which causes cessation of growth and then production. On the other hand, pH control at optimal value for LAB growth allows to overcome product inhibition (by the total lactic acid produced or its undissociated part); hence nutritional limitations have to be considered for model development. Nitrogen is mainly involved in cessation of growth, owing to the fastidious nutritional requirements of LAB, while lactic acid production ceased when carbon was exhausted from the medium. The lack of substrate inhibition when usual concentrations of carbon substrate are used should be noted

Optimization of production of lactic acid fermentation

During lactic acid fermentation in batch and continuous culture using Lactobacillus helveticus, seed culture is usually carried out without pH control, while culture is carried out at pH controlled at the optimal value to overcome inhibitory effects. In this study, novel mathematical models are set up to describe lactic acid production in batch and continuous fermentation. The Luedeking-Piret expression was therefore previously modified by introducing additional terms involving the undissociated form of the lactic acid, the main inhibitory species, in case of batch cultures without pH control. To describe growth, the Verlhust model which proved to describe satisfactory growth kinetics was considered. The model was found to match both experimental growth and production data. Another model was also developed involving the residual lactose concentration to account for carbon substrate limitation, responsible for cessation of production during batch cultures of Lactobacillus helveticus at controlled pH. This model matched experimental data accurately. Two generalized models were then deduced from the above expressions. The results obtained show that the generalized models gave a satisfactory description of experimental data in various culture conditions, since they were validated during cultures at pH control and in absence of pH control, as well as for different nitrogen supplementation of culture media. Both models, as well as the Luedeking-Piret model, were developed to describe successfully continuous two-stage culture of L. helveticusAu cours de la fermentation lactique en discontinu ou en continu, la préculture se fait généralement à pH libre tandis que la culture se fait à pH régulé, et ce pour éviter une inhibition par l acide formé. Dans ce travail, de nouveaux modèles mathématiques ont été développés pour décrire la croissance et la production d'acide lactique. Le modèle de Luedeking-Piret a été modifié en introduisant, d'une part, l'effet inhibiteur de l'acide lactique non dissocié dans le cas de la préculture. Pour la croissance, le modèle de Verlhust a été utilisé dans ce travail. Le modèle développé décrit correctement les résultats expérimentaux jusqu'à la fin de la fermentation. D'autre part, afin de rendre compte d une limitation nutritionnelle, ce qui est le cas lors de l étape de culture (à pH régulé) un second modèle a été développé en introduisant la concentration résiduelle en substrat carboné. Pour éviter l'utilisation des deux modèles précités, deux modèles généralisés ont été développés qui tiennent compte à la fois de l'effet inhibiteur de l'acide lactique non dissocié et des limitations nutritionnelles. Ces modèles décrivent bien les résultats expérimentaux à pH libre et à pH régulé. Ces modèles ont été appliqués avec succès au cas d'un bioréacteur biétagé en continu.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Adsorption of the Cationic Dye Ethyl Violet on Acid and Alkali-Treated Wild Carob Powder, A Low-Cost Adsorbent Derived from Forest Waste

International audienceThe effect of acid-alkaline treatment of lignocellulosic material (wild carob forest wastes) on Ethyl violet adsorption was investigated. It was found that surface chemistry plays an important role in Ethyl Violet (EV) adsorption. HCl treatment produces more active acidic surface groups such as carboxylic and lactone, resulting in an increase in the adsorption of EV dye. The adsorption efficiency was higher for treated lignocellulosic material with HCl (WCHCl) compared to that treated with KOH (WCKOH); maximum biosorption capacities were 170 and 130 mg/g for WCHCl and WCKOH at pH 6, respectively. It was also found that for both treated materials less than 150 min was needed to reach equilibrium. The adsorption of a basic dye (i.e. ethyl violet or basic violet 4) was carried out by varying some process parameters, such as the initial concentration and pH. The adsorption process can be well described by means of a pseudo-second-order reaction model and experimental data were accurately expressed by the Sips and Langmuir models for both WCHCl and WCKOH

Adsorption of ethyl violet dye in aqueous solution by forest wastes, wild carob

International audienceThe adsorption of basic dye (i.e. ethyl violet (EV) or basic violet 4) from aq. solns. onto the forest waste non-modified wild carob (NMWC) was carried out by varying some process parameters, such as initial concn., pH, and temp. The exptl. results showed that an increase in the pH from 2 to 7 led to a strong decrease in the adsorption capacity of the dye (EV) on NMWC, showing the predominance of the dispersion forces compared to the electrostatic interactions, owing to the cationic character of the dye and the pHpzc of the biosorbent (∼6). The adsorption process can be well described by means of a pseudo-second-order reaction model showing that boundary layer resistance was not the rate-limiting step, as confirmed by intraparticle diffusion. In addn., exptl. data were accurately expressed by the Sips equation if compared with the Langmuir and Freundlich isotherms. The high "m" values of the Sips model characterized a multilayer adsorption and the max. amt. adsorbed given by the Sips model was 100.4 mg/g at 20°C, namely close to the exptl. value and increased only weakly with the temp. The values of ΔG0 and ΔH0 confirmed that the adsorption of EV on NMWC was spontaneous and endothermic in nature. The pos. values of ΔS0 suggested an irregular increase in the randomness at the NMWC-soln. interface during the adsorption process

Improved growth model for two-stage continuous cultures of Lactobacillus helveticus

International audienceAn unstructured model for growth and lactic acid production during two-stage continuous cultures of Lactobacillus helveticus was previously developed. The Verlhust model was considered to describe growth kinetics. Production models was based on modified Luedeking-Piret expressions involving an inhibitory effect for the first stage (seed culture) and a nutritional limitation effect for the second stage (culture). To account for the decrease of the biomass concentration observed in the second stage, the dilution rate Dc was replaced by an exponential term of the dilution rate in the growth and product relations. Contrarily to the previous model, the important decrease of the biomass concentration observed at steady state in the second stage at high dilution rates, namely close to wash out, was correctly described by the new model. It also proved to satisfactory describes production data and volumetric productivity

A New Mg-Al-Cu-Fe-LDH Composite to Enhance the Adsorption of Acid Red 66 Dye Characterization, Kinetics and Isotherm Analysis

International audienc

Novel Fe2TiO5/reduced graphene oxide heterojunction photocatalyst with improved adsorption capacity and visible light photoactivity: experimental and DFT approach

International audienceThe design of high-efficiency materials is a major challenge for the degradation of organic pollutants. In this work, type IIp-nheterojunction photocatalyst Fe2TiO5/rGO, with enhanced performance, was successfully prepared through simple process. The Fe2TiO5/rGO composites were prepared by hosting several amounts of reduced graphene oxide (rGO) into pseudobrookite nanocrystals (Fe2TiO5) which were priorly synthesized by a solid-state reaction. The morphology and the properties of the as-prepared composites were characterized through different techniques. The fixation of rGO sheets on Fe(2)TiO(5)was proved using the X-ray diffraction analysis (XRD). The results of the scanning electron microscope (SEM) analysis showed a good mixing of rGO with Fe2TiO5. The X-ray fluorescence (XRF) confirmed the purity of the pristine Fe2TiO5. The dynamic light scattering (DLS) illustrated a strong tendency to aggregation. Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) analysis was performed to characterize the electronic aspect as the gap and the Urbach energies. Finally, computational density functional theory (DFT) calculations were carried out to confirm the experimental results. The adsorptive and photoactivity of Fe2TiO5/rGO heterojunction photocatalysts were evaluated by methylene blue (MB) degradation under visible light irradiation. The highest MB degradation rate was achieved for Fe2TiO5/rGO(10%)photocatalyst with the highest value of the elimination rate