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In the present work, L-glutamic acid production by Corynebacterium glutamicum fermentation on date juice extracts applying two fed-batch feeding modes, pulsed and continuous, were investigated. According to the obtained results, the continuous feeding fed-batch mode was found to be the most efficient process. Moreover the continuous feeding rate mode with a feeding medium containing date juice sugars enriched with ammonium sulfate was found even more favorable as it enhances the L-glutamic acid production by approximately 2.35 fold more than the batch culture and by about 1.17 fold more than the pulsed feeding. In this respect, comparing the traditional batch culture to the continuously fed culture with a medium containing date juice sugars with ammonium sulfate showed increases of 135.47% in L-glutamic acid production, 104% in productivity, 39.09% in biomass, and 47.69% in the yield respectively allowing us to reach a final L-glutamic acid concentration of about 138 g/L, the highest ever published.

Opuntia ficus indica (OFI) waste was evaluated as a fermentation feedstock for lactic acid production using Lactobacillus plantarum. Dilute acid pretreatment of the OFI cladodes (OFIC) was performed for extracting maximum fermentable sugars by optimizing process parameters using statistical optimization method. The best results were obtained with HCl 1% (v/v), temperature 120 ◦C, residence time 40 min, granulation 350 μm and substrate loading 5% (w/v), the sugar concentration reached 24 g/L with low concentration of hydroxymethylfurfural. The feasibility of producing lactic acid from OFI fruit peel (OFIFP) as a source of carbon was also investigated. Lactobacillus plantarum was shown to have a capacity for lactic acid production from OFIC350 (granulation 350 μm) hydrolysate and OFIFP extract without detoxification. The highest lactic acid yields of 0.46 and 0.78 g/g were obtained from enzymatic hydrolysate of pretreated OFIC350 and OFIFP extract, respectively. info:eu-repo/semantics/publishedVersion

The feasibility of baker's yeast production using fruits and peels of Opuntia ficus indica (OFI) as carbohydrate feedstock was investigated. Two response surface methodologies involving central composite face centered design (CCFD) were successfully applied. The effects of four independent variables on baker's yeast production from OFI fruit juice was evaluated using the first CCFD. The best results were obtained with 24 H of inoculum age, 30 degrees C temperature, 200 rpm of agitation, and 10% inoculum size. At the maximum point, the biomass concentration reached 9.29 g/L. A second CCFD was performed to optimize the sugar extraction from OFI fruit peels. The potential of these latter as a fermentation substrate was determined. From the experimental results, the OFI fruit peel is an appropriate carbon source for the production of baker's yeast. The maximum biomass concentration was 12.51 g/L. Different nitrogen supplements were added to promote the yields of baker's yeast. Corn steep liquor was found to be the best alternative nutrient source of casein hydrolysate and yeast extract for baker's yeast production. info:eu-repo/semantics/publishedVersion

The production of lactic acid from date juice by Lactobacillus caseisubsp. rhamnosus in batch and fed-batch cultures has been investigated. The fed-batch culture system gave better results for lactic acid production and volumetric productivity. The aim of this work is to determine the effects of the feeding rate and the concentration of the feeding medium containing date juice glucose on the cell growth, the consumption of glucose and the lactic acid production by Lactobacillus casei subsp. rhamnosus in fed-batch cultures. For this study, two concentrations of the feeding medium (62 and 100 g/L of date juice glucose) were tested at different feeding rates (18, 22, 33, 75 and 150 mL/h). The highest volumetric productivity (1.3 g/L.h) and lactic acid yield (1.7 g/g) were obtained at a feeding rate of 33 mL/h and a date juice glucose concentration of 62 g/L in the feeding medium. As a result, most of the date juice glucose was completely utilised (residual glucose 1 g/L), and a maximum lactic acid production level (89.2 g/L) was obtained.

Sawdust wood (SW) is a promising lignocellulosic biomass for lactic acid production due to its abundant availability, low cost and high carbohydrates content that can be converted to fermentable sugars. The dilute acid hydrolysis of SW was investigated in this study and Lactococcus lactis was used to determine the feasibility of utilizing WS as feedstock for the production of lactic acid. Central composite design (CCD) was employed to optimize sulfuric acid, substrate loading and hydrolysis time for maximum sugar recovery. The results obtained were interpreted by analysis of variance and response surface methodology. The optimal acid hydrolysis conditions were as follows: sulfuric acid concentration of 8% (v/v) with substrate loading of 16% (w/v) and hydrolysis time of 2h. Under the optimal conditions, a glucose concentration of 8.78g/L was achieved. A regression model was generated according to the experimental data. Upon statistical analysis, coefficient of determination (R2 ) obtained was 0.96. Lactococcus lactis was found to be a potent lactic acid bacteria (LAB) strain for the production of lactic acid utilizing acid hydrolysate of WS and yeast extract as carbon and nitrogen sources, respectively. The maximum lactic acid concentration of 9.87g/L was obtained with a yield of 1.1g/g.

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International audience; Waste valorization practices have attracted a significant amount of attention in recent years with the aim of managing waste in the most sustainable way. Food waste constitutes a largely under-exploited residue from which a variety of valuable chemicals can be derived. The operation in global yoghurt market provokes frequently the reject and withdrawn of yoghurt derivates out of shelf life. This work comprises a contribution on the valorisation of this high polluting waste of the dairy industry, based on the production of lactic acid using residual yoghurt whey as raw material. Response surface methodology (RSM) based on central composite design (CCD) was used to evaluate the effects of fermentation parameters for lactic acid production by Lactococcus lactis subsp. in batch experiments. The critical factors selected for the investigation were: sugars concentration (X1), yeast extract concentration (X2) and inoculum size (X3). The experimental results were fitted with a second order polynomial equation by a regression analysis and 93% of the variation could be predicted by the model. A maximum lactic acid production (6.80 g/l) was obtained under following optimal conditions: sugars concentration 57 g/l, yeast extract concentration 10.8 g/l and inoculum size 10 %. Moreover, the maximum of lactic acid production predicted by the model was 6.61 g/l. These results confirmed the validity of the model, and the experimental values were quite close to the predicted values

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International audience; The production of lactic acid from date juice by single and mixed cultures of Lactobacillus casei and Lactococcus lactis was investigated. In the present conditions, the highest concentration of lactic acid (60.3�g�l?1) was obtained in the mixed culture system while in single culture fermentations of Lactobacillus casei or Lactococcus lactis, the maximum concentration of lactic acid was 53 and 46�g�l?1, respectively. In the case of single Lactobacillus casei or Lactococcus lactis, the total percentage of glucose and fructose utilized were 82.2; 94.4% and 93.8; 60.3%, respectively, whereas in the case of mixed culture, the total percentage of glucose and fructose were 96 and 100%, respectively. These results showed that the mixed culture system gave better results than single cultures regarding lactic acid concentration, and sugar consumption.

The production of lactic acid from date juice by Lactobacillus caseisubsp. rhamnosus in batch and fed-batch cultures has been investigated. The fed-batch culture system gave better results for lactic acid production and volumetric productivity. The aim of this work is to determine the effects of the feeding rate and the concentration of the feeding medium containing date juice glucose on the cell growth, the consumption of glucose and the lactic acid production by Lactobacillus casei subsp. rhamnosus in fed-batch cultures. For this study, two concentrations of the feeding medium (62 and 100 g/L of date juice glucose) were tested at different feeding rates (18, 22, 33, 75 and 150 mL/h). The highest volumetric productivity (1.3 g/L.h) and lactic acid yield (1.7 g/g) were obtained at a feeding rate of 33 mL/h and a date juice glucose concentration of 62 g/L in the feeding medium. As a result, most of the date juice glucose was completely utilised (residual glucose 1 g/L), and a maximum lactic acid production level (89.2 g/L) was obtained.

The production of lactic acid from date juice by Lactobacillus caseisubsp. rhamnosus in batch and fed-batch cultures has been investigated. The fed-batch culture system gave better results for lactic acid production and volumetric productivity. The aim of this work is to determine the effects of the feeding rate and the concentration of the feeding medium containing date juice glucose on the cell growth, the consumption of glucose and the lactic acid production by Lactobacillus casei subsp. rhamnosus in fed-batch cultures. For this study, two concentrations of the feeding medium (62 and 100 g/L of date juice glucose) were tested at different feeding rates (18, 22, 33, 75 and 150 mL/h). The highest volumetric productivity (1.3 g/L.h) and lactic acid yield (1.7 g/g) were obtained at a feeding rate of 33 mL/h and a date juice glucose concentration of 62 g/L in the feeding medium. As a result, most of the date juice glucose was completely utilised (residual glucose 1 g/L), and a maximum lactic acid production level (89.2 g/L) was obtained.

International audience; o improve glutamic acid production from Corynebacterium glutamicum 2262 using date juice, a culture medium was screened and optimized using the statistical experimental designs of Plackett-Burman and response-surface methodology. In the first step, a two-level Plackett-Burman design was adopted to select the most important nutrients influencing the glutamic acid production, which showed that the date juice sugars, urea, peptone, and glycine betaine were the most significant ingredients (P < 0.05). Finally, response surface Box-Behnken design was employed to develop a mathematical model to identify the optimum concentrations of key components for higher glutamic acid production, which revealed the following: date juice (45 g/L), urea (16.9 g/L), peptone (15 g/L), and glycine betaine (12 g/L). The high correlation between the predicted and observed values indicated the validity of the model. Glutamic acid concentration increased significantly with optimized medium (33.2 g/L) when compared with non-optimized medium (12 g/L).

The use of date juice as a substrate for lactic acid production was investigated. Various nitrogen sources were compared with yeast extract for efficient lactic acid production by Lactobacillus casei subsp. rhamnosus. Among different nitrogen sources added to date juice (yeast extract, ammonium sulfate, tryptic soy, urea, peptone, and casein hydrolysate), yeast extract was the most efficient. The effect of yeast extract could have been due to its B vitamin content. The addition of five B vitamins at less than 25 mg/l to date juice with any nitrogen source enhanced lactic acid production to some extent, except for date juice with yeast extract or urea or peptone. The most significant increase was obtained with ammonium sulfate. Half of the yeast extract content (10 g/l) in a supplemented date juice could be replaced by a mixture of B vitamins at less than 25 mg/l, and ammonium sulfate at 2.6 g/l with no significant decrease in lactic acid production.

Date-coat sugar extract and date-seed hydrolysate were utilized as the main constituents of a medium for the production of a thermophilic dairy starter strain. Date-coat sugar extract was used as the carbon source, while date-seed hydrolysate was used as the nitrogen source. A suitable concentration of date-coat sugar was in the range of 50 mg sugar/ml. Addition of various amounts of date-seed hydrolysate as the sole nitrogen source in the medium showed that, in spite of a nitrogen insufficiency found in the hydrolysate, the production of the starter strain increased with date-seed hydrolysate (nitrogen) concentration, but the maximum production of biomass was less than that observed with other nitrogen sources. Therefore, various amounts of urea were added and a mixture of urea (6 mg/ml) and of date-seed hydrolysate (4.0 mg/ml) allowed an increase in the concentration of the biomass. The addition of date-seed ash as a mineral source, at a concentration of 1.0 mg/ml in the medium containing date-coat sugar extract, date-seed hydrolysate, and urea could substitute for MgSO4, and MnSO4 of the usual medium. This medium gave the maximum production of the thermophilic lactic acid bacteria (0.57 mg/ml) and lactic acid (2 mg/ml), very close to what was obtained with the Elliker broth medium.

This work was an approach to waste date products valorization through biomass production with the yeast Saccharomyces cerevisiae. The carbon and nitrogen sources of a semi-synthetic fermentation medium were substituted by date-coat (fleshy part) sugar extract, date-seed hydrolysate, and ammonium nitrate. This modified medium was enriched with date-seed ash and date-seed lipid. Date-coat sugar extract as a carbon source was found to be satisfactory at a concentration of 25 g/l (expressed as its glucose concentration) and date-seed hydrolysate as a nitrogen source was equally suitable at 25 g/l. The addition to the medium of 1·0 g/l ammonium nitrate increased the efficiency of yeast biomass formation, as did phosphorus, which produced a maximum when the medium was supplemented with about 6·0 g/l KH 2 PO 4 . The presence of 1 g/l date-seed lipid in the medium also increased the efficiency of biomass formation. Finally, the addition of date-seed ash (0·6 g/l), as a mineral source, to the fermentation medium could substitute for MgSO 4 and CaCl 2 of the semi-synthetic medium.

The aim of this work was to develop an efficient process of lactic acid production by Lactobacillus casei subsp. rhamnosus on date juice In a first part, the batch cultures were realized to carry out the nutritional requirement of the strain. These studies allowed us to describe the effects of carbon substrates, nitrogen substrates and vitamins on the lactic acid production. We showed that ammonium sulphate is a satisfying economic alternative and we have determined feasibility of minimizing the addition of the yeast extract by the partial use of yeast extract combined with the ammonium sulphate plus the addition of vitamins of the group B. Pure and mixed cultures of Lactobacillus casei and Lactococcus lactis were carried out. The mixed system gives better results concerning the lactic acid production and the use of the sugars compared with those obtained in pure cultures of Lactobacillus casei or Lactococcus lactis. The effect of pure sugars (glucose and fructose) and mixed sugars (glucose/fructose) on the lactic acid production was studied. The lactic acid production is more important on mixed sugars than on pure sugars what explains the performances of fermentation on date juice. In a second part, a mode of fed batch operations was defined to improve the performances of the fermentation. The two factors influencing the process are the feeding rate and the concentration of the feeding medium. In a third part, kinetic study in continuous culture was developed. We studied the influence of dilution rate on growth, substrate utilization and lactic acid production. The productivity of the continuous process was considerably increased in comparison with the batch process. Finally, a tentative model has been established for the fermentation process. The corresponding model, although not perfect, is apparently able to simulate growth rate, substrates uptake and lactic acid production in batch culture; L'objectif de ce travail a été de développer un procédé performant de production d'acide lactique par Lactobacillus casei subsp. rhamnosus sur jus de datte. Dans une première partie, des cultures en mode discontinu ont été réalisées afin d'étudier les besoins nutritionnels de la souche. Ces études ont pour but de décrire les effets des sources carbonées, azotées et les vitamines sur la production d'acide lactique. Nous avons montré que le sulfate d'ammonium est une bonne alternative économique et nous avons pu déterminer la faisabilité de minimiser l'ajout de l'extrait de levure par l'utilisation partielle de l'extrait de levure combinée avec du sulfate d'ammonium plus l'ajout de vitamines du groupe B. Des cultures pures et mixtes de Lactobacillus casei et Lactococcus lactis ont été réalisées. Le système de culture mixte donne de meilleurs résultats concernant la production d'acide lactique et l'utilisation des sucres comparés à ceux obtenus en cultures pures de Lactobacillus casei ou Lactococcus lactis. L'effet des sucres purs (glucose et fructose) et mixtes (glucose/fructose) sur la production d'acide lactique a été étudié. La production d'acide lactique est plus importante avec un mélange de sucres qu'avec des sucres non mélangés ce qui explique les performances de fermentation sur jus de datte. Dans une seconde partie, une stratégie d'alimentation du réacteur en culture semi-continue a été mise en oeuvre, permettant d'améliorer les performances de la fermentation. Les deux facteurs influençant le bon fonctionnement sont le débit et la concentration du milieu d'alimentation. Dans une troisième partie, une étude cinétique a été développée en réacteurs continus. Nous avons étudié l'influence du taux de dilution sur la croissance, l'utilisation du substrat et la production d'acide lactique. La productivité du procédé continu a été considérablement augmentée en comparaison avec le procédé discontinu. Enfin, dans une dernière partie, un modèle a été établi. Ce modèle, bien qu'imparfait, permet apparemment de simuler la croissance, la consommation des sucres de jus de datte et la production d'acide lactique en culture discontinue

The kinetics of growth, substrate consumption and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) production by Escherichia coli C600 galK (GAPDH) have been studied. Using the corresponding observations, an unstructured physiological model has allowed description of the behaviour of the recombinant strain in batch culture on a selective complex medium. This model is characterized by two physiological states (glucose and acetic acid consumption) and is based on the Monod equation applied to the growth rate combined with inhibition by acetate. Since the strain used is genetically engineered, it also incorporates the probability of plasmid loss which has been modelled previously. The model has been applied to a set of batch cultures at varying initial glucose concentrations. According to the simulation results, the model provides an excellent fit to the experimental results.

A large number of models concerning cultures of genetically engineered bacteria have been described. Among them, some are specifically adapted to continuous cultures and lead to the determination of two variables: (i) the difference in the specific growth rates between plasmid-carrying cell and plasmid-free cells (deltamicro) and (ii) the frequency of plasmid loss by plasmid-containing cells (p(r)micro(+)). Until now, studies have been performed on the global expression p(r)micro(+) and deltamicro, whose value during continuous assays have been supposed approximately constant (mean value) and not on separate values of both terms p(r) and micro(+), respectively, probability of plasmid loss and specific growth rate of the plasmid-carrying cells. So far these studies do not allow examination of the relationship between these two last parameters. Experimental results were obtained with Escherichia coli C600 galk (GAPDH), a genetically engineered strain that synthetizes an elevated quantity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). From data obtained during continuous cultures, it is shown that during an assay, deltamicro, and p(r)micro(+) do not remain constant. An appropriate mathematical analysis of the expression of micro(-) (specific growth rate of the plasmid-free cells) and micro(+) has been built up. This allows the evaluation of the values of micro(+) and micro(-) during the continuous cultures carried out at different dilution rates. Values of p(r) have been calculated from these data. Indeed our results show that p(r) increases with micro(+). A modeling approach which allows correct simulation of this variation is also proposed. This model is derived from the Hill equation regarding cooperative binding of enzymic type reaction.

Experimental results were obtained withEscherichia coli C600 galK (GAPDH), a genetically engineered strain that synthetizes a large quantity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), (80 % of the soluble proteins). Data concerning the stability of plasmid-containing cells and gene expression as a function of dilution rate have been obtained in continuous cultures. Contrary to other studies, our results show a clear indication that the rate of the recombinant activity was dependent on dilution rate. The results support the finding that the apparent stability of the plasmid decreases with dilution rate.

A numerical method to process experimental data concerning plasmid stability of a recombinant bacteria during continuous cultures with nonselective media is proposed here. This method differs from previous ones in that it uses the derivatve form of the state equation of the Imanaka-Aiba model for recombinant cultures. The methodology proposed here allows one to estimate values for the two model parameters without forcing them to be constant. Until now, this could not be done using classical analytical techniques because these parameters have been considered invariable because of the integration used in the evaluation of the model. These parameters are (1) the difference in the specific growth rates between plasmid-carrying cells and plasmid-free cells (deltamu), and (2) the probability of plasmid loss by plasmid-containing cells (rho(r) mu(+)). The derivative technique used here is completed by mathematical treatments involving data filtering and smoothing. The values of the two parameters are in agreement with those already published. The current technique does not impose preconditions and permit us to further study related phenomena.

Modelling of plasmid containing cell cultures aids in developing a greater understanding of these complex systems. For such modelling, a number of investigators have introduced key kinetic parameters: the frequency of generation of plasmid-free daughter cells from plasmid-carrying mother cells, the specific growth rate difference between plasmid-carrying (µ+) and plasmid-free cells (µ-) and the probability of plasmid loss pr [1,2,3]. However, little experimental data have been reported [4,5]. In the previous paper the probability of plasmid loss pr varies with the growth rate of the plasmid-carrying cells µ+ [6]. We propose a modelling approach, allowing the simulation of this variation.

Not available, Ce travail concerne la mise en œuvre de la souche recombinée d'e. Coli c600 galk (GAPDH). Cette souche produit des quantités importantes de la protéine recombinante. Une étude du comportement de la souche sur milieu complexe a été faite. Les acides aminés d'auxotrophie permettent de stabiliser la protéine produite. L'extrait de levure permet l'utilisation de l'acétate, la peptone, la stabilisation de la GAPDH. Nous avons étudié l'influence du taux de dilution sur la stabilité plasmidique et sur l'activité enzymatique de la GAPDH en culture continue sur milieu complexe non sélectif. Les résultats ont montré que la fraction de cellules contenant les plasmides décroit avec le taux de dilution. Ces résultats montrent que l'activité enzymatique de la GAPDH est dépendante du taux de dilution, ce qui est différent des observations faites dans d'autres études. Une méthode originale d'estimation des deux principaux paramètres du modèle d'imanaka et aiba, modèle permettant de caractériser l'instabilité de souches recombinées est proposée. La valeur de ces paramètres a été déterminée en utilisant la forme dérivée du modèle précité combine à un filtrage et un lissage numériques. Des modèles spécifiques ont été construits. Celui décrivant l'évolution de la probabilité de perte de plasmide en fonction du taux de croissance spécifique repose sur l'analogie entre la variation du nombre de copies de plasmide et la probabilité de perte observée. Enfin, un modèle mathématique permettant de simuler le procédé en discontinu sur une gamme de concentrations initiales en glucose est propose. Il permet également de modéliser correctement, les consommations du glucose, de l'acide acétique ainsi que la production de la biomasse et de l'enzyme

The influence of complex compounds on the growth of a recombinant strain of Escherichia coli containing the gene encoding glyceraldehyde 3-phosphate dehydrogenase, as well as the production of this enzyme have been studied. Batchwise cultures led to an accumulation of acetate, which was not utilized in a yeast extract-free medium. After glucose exhaustion, growth stopped and enzyme activity decreased. Whereas yeast extract allowed acetate assimilation and growth, peptone stabilized the enzymatic activity. The addition of both compounds resulted in optimal performances for enzyme production.

A high productivity process for glyceraldehyde-3-phosphate dehydrogenase using a strain ofEscherichia coli genetically modified for the high production of this enzyme is described. The fermentation is srongly dependent on the levels of essential nutrients, implying strict physiological control of the gene expression.