Chemical engineering aspects of submerged production of citric acid

We determined the total mass balance of production of citric acid byAspergillus niger on the laboratory scale and derived a stoichiometric equation for optimum conditions. At the aeration intensity of 4.10^-3 m³/min, 2/3 of introduced carbon was found to be converted to citric acid. Other parameters were: rate of absorptionNa, 15 –17 mol^-3h^-1 and oxygen utilization equal to 42 % of sugar mass. The critical concentration of dissolved oxygen,i.e. 9.5 % of saturation level, was not exceeded.     

Penicillic acid production in submerged culture.

Twenty known penicillic acid (PA)-producing Aspergillus and Penicillium cultures were grown under various conditions in shaken flasks to determine the highest yielding strains and their requirements for maximum toxin production. Abilities of the cultures to utilize eight different carbon sources in Raulin-Thom medium for mycotoxin synthesis were determined at four different incubation temperatures: 15, 20, 25, and 28 degrees C. Of the 20 cultures, P. cyclopium NRRL 1888 was superior, yielding up to 4 mg of PG per ml, with mannitol as the carbon source and 25 degrees C as the incubation temperature. Fifteen of the cultures elaborated lesser amounts of PA, whereas four strains yielded none under the test conditions. Whey from the manufacture of cottage cheese by the cultured process was also a satisfactory medium for PA production. In whey medium, yields up to 3 mg/ml were obtained with P. cyclopium NRRL 1888.     

Penicillic acid production in submerged culture.

Twenty known penicillic acid (PA)-producing Aspergillus and Penicillium cultures were grown under various conditions in shaken flasks to determine the highest yielding strains and their requirements for maximum toxin production. Abilities of the cultures to utilize eight different carbon sources in Raulin-Thom medium for mycotoxin synthesis were determined at four different incubation temperatures: 15, 20, 25, and 28 degrees C. Of the 20 cultures, P. cyclopium NRRL 1888 was superior, yielding up to 4 mg of PG per ml, with mannitol as the carbon source and 25 degrees C as the incubation temperature. Fifteen of the cultures elaborated lesser amounts of PA, whereas four strains yielded none under the test conditions. Whey from the manufacture of cottage cheese by the cultured process was also a satisfactory medium for PA production. In whey medium, yields up to 3 mg/ml were obtained with P. cyclopium NRRL 1888.     

A comparison of factors influencing citric acid production by Aspergillus niger grown in submerged culture and on filter paper

Summary A filter paper surface cultivation method (previously described as a tool for strain selection by Röhr et al. 1979) was adopted as a cultivation system for citric acid production on a small scale and compared with submerged cultivation. Citric acid production in the submerged system was optimal at defined low concentrations of zinc, ferrous and manganese ions, defined phosphate and nitrogen concentrations and within a defined initial pH. In constrast, citric acid production in the filter paper system was not at all influenced by any of these variables. On the other hand, optimal citrate production in both systems required a high (10%–14%, w/v) sucrose concentration. This identifies sugar concentration as a most significant parameter for citrate production, whereas all other nutritional effects are related to the cultivation system used.     

Redox potential in submerged citric acid fermentation

Summary The role and importance of the redox potential phenomena in submerged citric acid production are discussed. The redox potential of the fermentation broth is the result of oxydo-reduction processes where the metabolic activity of the microorganism Aspergillus niger plays the most significant role. The course of the redox curve for a good yielding citric acid production is presented and interpreted. The experiments of submerged citric acid production were carried out on beet molasses treated with potassium hexacyanoferrate and inoculated with A. niger spores.     

Application of carbon balance to submerged citric acid production by Aspergillus niger

Summary In an air-lift fermenter, the following production was obtained from 125 g sucrose in mineral medium at pH 2.5 : 15.76 g mycelium dry wt, 107.2 g citric acid anhydrous and 0.594 mol CO₂ within 138 h (run I) and 13.72 g mycelium dry wt, 114.28 g citric acid and 0.516 mol CO₂ within 144 h (run II). Initially, the carbon content of consumed sugar and products did not balance. At the end of fermentation, the carbon content of the products was 0.9%–5.5% higher than that of the consumed sugar. For the purpose of the calculations the carbon content in mycelium was accepted as 0.462.The work was a part of Project No 04.11 CPBP, topic No 2.24     

Short communication: Influence of inoculum preparation on citric acid production by Aspergillus niger

The type of sporulation medium and time of incubation had an effect on spore viability and citric acid production by mycelia grown from Aspergillus niger spores. Shu & Johnson agar (SJA) and potato dextrose agar gave higher citric acid titres than malt-extract agar. SJA also gave better germinability than the other media. Viability increased with time of incubation, but higher production of citric acid was achieved with spores incubated for less than 7 days.     

Mathematical modeling of citric acid production by repeated batch culture

A mathematical model has been created for the process of citric acid biosynthesis by yeast (mutant strain Yarrowia lipolytica) cultivated by the repeated batch (RB) method on ethanol under conditions of nitrogen limitation. The model accounts for cell growth as a function of nitrogen concentration in the culture liquid; nitrogen uptake by growing cells; citric acid production; pH control in the fermentor by means of NaOH addition; and changes in system volume. The model represents a system of five nonlinear differential equations. Experimental measurements of cell concentration, citric acid concentration, and cultivation broth volume were used with the least squares method to determine the values of eight model parameters. The parameter values obtained were consistent with literature data and general concepts of cell growth and citric acid biosynthesis. The model has been used to predict optimum RB culture conditions.     

The effect of citric acid concentration and pH on the submerged production of lysergic acid derivatives

Summary Succinic acid can just as well be replaced by citric acid in submerged fermentation of lysergic acid derivatives by a strain of Claviceps paspali. The highest alkaloid yields were obtained with a 1% citric acid concentration in the medium at a constant pH of 5.2. When the optimal pH was not maintained, growth was inhibited and all aspects of metabolic activity of the fungus were depressed.     

Foaming in submerged citric acid fermentation on beet molasses

Summary Foam control is an important part of every fermentation technology. Chemical anti-foam agents (AFA) are surface active substances, which decrease the surface elasticity of liquids and prevent metastable foam formation. Most AFA must be mixed or dissolved in a suitable carrier substance if their antifoaming properties are to be fully utilized. The carrier seems to act as a reservoir from which the AFA is liberated.The toxicity of different AFA upon Aspergillus niger was tested in Petri dishes. Their effect on the decrease of the respiration ability of the test organism A. niger was tested in a Warburg apparatus. Various AFA were tested as pure substances, as emulsions in seed oil and as mixtures of different AFA in cylindrical vessels with sinter glass discs under similar conditions as in the fermentor. Using mentioned methods the most suitable AFA were tested in citric acid fermentation on beet molasses.Partly presented at the poster session of the meeting: Fungal Biotechnology, Glasgow, September 1978     

Rosmarinic acid production in perfused Anchusa officinalis culture: Effect of inoculum size

Summary High cell density and rosmarinic acid (RA) productivity have been achieved by applying periodic culture perfusion to the Anchusa officinalis cell suspension. In this study, the effect of inoculum size on cell growth and RA productivity in the perfused Anchusa culture was investigated. Experimental results showed that RA productivity increased with the inoculum size, up to 4 g dry weight/L. Further increases in the inoculum size did not yield a higher RA productivity regardless of culture perfusion. Moreover, the maximum cell concentration was not affected by the inoculum sizes, from 1 to 11 g dry weight/L. Cell crowding, indicated by high culture packed cell volumes, is believed to be the predominant cause of low productivity in perfused cultures with high inoculum sizes.     

The effect of acetate on the production of citric acid by Aspergillus niger in submerged fermentation

Summary Two strains of Aspergillus niger showed a 57% and 40% reduction in growth in a shaken mineral medium with 5% glucose, at the initial pH 6.5–6.0 where ammonium acetate (0.25% and 0.2%) was a source of nitrogen. Uptake of glucose was not inhibited and mycelium kept its acid-forming activity. Growth inhibition was abolished in the presence of 12% glucose or increased content of ammonium and sodium acetate up to 765 mg acetate anion per 100 cm³.This work was a part of Project MR II, 17, topic no. 2.3.2.     

A novel recycling process using the treated citric acid wastewater as ingredients water for citric acid production

In this study, an integrated process coupling citric acid and methane fermentations was proposed to solve severe wastewater pollution problem in cassava-based citric acid production. The accumulation patterns of the potential and major inhibitors in this process, including organic compounds, volatile fatty acids (VFAs), total ions and pigments were investigated. Both simulation and experimental results indicated that these inhibitors could reach their equilibrium levels after 3–7 fermentation runs when reutilizing the treated citric acid wastewater. As a result, the proposed citric acid fermentation process by recycling the wastewater treated in methane fermentation could be stably operated for more than 15 runs, which could save a large amount of fresh water and relieve the severe wastewater pollution in citric acid production potentially.     

Citric acid production in submerged and solid state culture of Aspergillus niger

In this work, the citric acid production in solid state culture was performed, evaluating the isolated effect and interactions of particle size and liquid phase employed, by means of the factorial design of first order. The results indicate that the particle size is the most determinant variable. An analysis comparing submerged and solid state in optimal conditions was performed. When solid state culture was used, the productivity of citric acid was doubled, reducing the fermentation time from 14 to 6 days, compared to the submerged culture, obtaining a maximum citric acid concentration of 21.24 g/l.List of Symbols B _s , B _v main effects - B _sv crossed effects - s cm particle size - S coded particle size - v ml liquid phase volume - V coded liquid phase volume     

Challenges for mass production of nematodes in submerged culture

Nematodes of Steinernema and Heterorhabditis genera are used as agents in insect biocontrol programs. They are associated with specific bacteria which are also involved in the mechanism of pathogenicity and which are consumed by nematodes as living food. S. feltiae has various developmental stages in its life cycle, including four juvenile stages, adults and the free living form. During mating, males coil themselves around the female, which is around 1 cm long. Successful commercialization of nematode-bacteria biocontrol products depends on the ability to produce sufficient quantities of these products at competitive prices for a full pest control program. This could be feasible if high cell density submerged cultures are designed and implemented; however, major problems related to nematodes mass production in a bioreactor remain unsolved due to the lack of knowledge about the physiological aspects of the nematode, bacteria and nematode-bacteria association, interaction between the three phases present in the bioreactor (liquid, gas, nematodes-bacteria), possibility of mating under hydrodynamic stress conditions, etc. We have found that the two most important engineering aspects to take into account the mass propagation of nematodes are oxygen transfer rate and hydrodynamics to allow mating and to avoid mechanical damage of juveniles in stage 2.This article focuses on several aspects related to the fermentation system such as kinetics of growth, shear stress, hydrodynamics fields in the bioreactor and oxygen demand. Also, results published by other groups, together with those of our own, will be discussed in relation to the main challenges found during the fermentation process.     

Production of citric acid in continuous culture

Work has been carried out on the production of citric acid by Aspergillus foetidus in single-stage continuous culture, operated under nitrogen-limiting conditions at dilution rates between 0.04 to 0.21 hr^?1. Citric acid concentration increased rapidly as the dilution rate decreased and appears to be critically dependent on the pH in the culture vessel and the nitrogen concentration in the feed. A mathematical model based on a distinction between basic cells, which require nitrogen but do not produce citric acid, and stroage cells, which accumulate carbon and simultaneously produce citric acid, is proposed.     

Fungal production of citric acid

Citric acid is the principal organic acid found in citrus fruits. To meet increasing demands it is produced from carbohydrate feedstock by fermentation with the fungus Aspergillus niger and the yeasts of Candida spp. Effect of various fermentation conditions and the biochemistry of citric acid formation by A. niger have been discussed. Commercially citric acid is produced by surface, submerged and solid state fermentation techniques. Recovery of pure acid from fermentation broth is done primarily by precipitation with lime and also by solvent extraction.