Influence of milk whey, nitrogen and phosphorus concentration on oxalic acid production by Aspergillus niger

A factorial design at two levels was used to determine the effect of milk whey concentration and the addition of nitrogen (as NH₄NO₃) and phosphorus (as KH₂PO₄) on the oxalic acid production by Aspergillus niger. The results of the experiments indicated that milk whey contains enough nutrients for fungus growth, therefore medium supplementing with N and P is not necessary. The optimum milk whey concentration was 100 kg/m³ reaching a final oxalic acid concentration of 37 kg/m³ and a maximum production rate of 3.4 kg/m³ · d. The yield of oxalic acid was 0.4, a very high value compared to previous works.     

The mutual influence of methanol and trace elements on the mycological production of citric acid

Summary The action of methanol on the stimulatory or inhibitory effect produced by certain trace elements on citric acid production by Aspergillus niger was investigated. Methanol addition masked the stimulatory action of zinc addition and also eliminated the inhibitory effect of iron and manganese. It was also remarkable that some of the trace elements masked the toxic action of methanol on both acid production and growth.     

Continuous production of citric acid from sugarcane molasses using a combination of submerged immobilized and surface stabilized cultures of Aspergillus niger KCU 520

Summary A high performance fermentation process for the continuous production of citric acid from sugarcane molasses by using the combination of submerged calcium alginate-immobilized and surface-stabilized cultures of Aspergillus niger KCU 520 in a continuous flow horizontal bioreactor is described. The citric acid productivity was dependent on the dilution rate with an optimum value of 0.015/h. Presaturation of fermentation medium with sterile air, in addition to surface aeration, before feeding into the bioreactor enhanced the citric acid productivity. The highest productivity, citric acid product concentration and yield obtained were 1.7 kg M^–3h^–1, 110kg M^–3 and 91% respectively. The cultures were continuously used for 30 days without any apparent loss in citric acid productivity.     

The effect of pH on production of citric and gluconic acid from beet molasses using continuous culture

Summary The effect of pH on the production of citric and gluconic acid, from beet molasses byAspergillus niger, was studied using continuous culture. At pH values above 2.5 gluconic acid was the major product, citric acid being the predominant product at low pH values. The optimum specific activities of citrate synthase, aconitase, NAD-linked isocitrate dehydrogenase, and NADP-linked isocitrate dehydrogenase occurred at pH 4 and of glucose oxidase at pH 5.     

Influence of nitrilotriacetic acid and 8-hydroxyquinoline on the production of citric acid from molasses using Aspergillus niger

The effect of nitriloacetic acid (NTA) and 8-hydroxyquinoline on the production of citric acid by Aspergillus niger was investigated. The complexing agents showed an effect only during inoculation of the microorganism. Subsequent addition after inoculation did not produce any significant increase in citric acid yield. When 200 ppm of NTA was added during inoculation, an increase of 10.9 g·dm⁻³ citric acid over that produced by the control culture was observed. 8-Hydroxyquinoline, on the other hand, produced a higher concentration of citric acid which was 34 g·dm⁻³ over that of the control culture. The use of 8-hydroxyquinoline is therefore suggested for the production of citric acid from molasses using Aspergillus niger.     

Channelling of glucose by methanol for citric acid production from Aspergillus niger

Citric acid produced by Aspergillus niger was increased from 4.6g l^-1 to 7.8gl^-1 by supplementing basal medium with methanol (30mll^-1). While stimulating citric acid production, methanol did not improve membrane permeability of the fungus for citric acid. Methanol inhibited the germination of Aspergillus spores. An increase in glucose concentration from 50gl^-1 to 100gl^-1 in the presence of methanol (30mll^-1) improved citric acid production (1.6-fold) while at higher levels of glucose concentration methanol had no effect on citic acid production.     

The kinetic basis of the role of Ca++ ions for higher yield of citric acid in a repeated-batch cultivation system

The present investigation deals with role of Ca⁺⁺ ions in increasing the yield of citric acid in a repeated-batch cultivation system (working volume 9-1) and its kinetic basis. Five different hyper-producing strains of Aspergillus niger were evaluated for citric acid production using clarified cane-molasses as basal substrate. Among the cultures, NG^GCB101 (developed by u.v./chemical mutation in our labs) gave maximum production of citric acid i.e., 87.98 g/1, 6 days after mycelial inoculation. The addition of CaCl₂ to the culture medium promoted the formation of small rounded fluffy pellets (1.55 mm, diameter), which were desirable for citric acid productivity. CaCl₂ at a level of 2.0 M, added during inoculation time, was optimized for commercial exploitation of molasses. During repeated-batch culturing, a yield of citric acid monohydrate of 128.68 g/1 was obtained when the sampling vs. substrate feeding was maintained at 4-1 (44.50% working volume). The incubation period was reduced from 6 to only 2 days. The values of kinetic parameters such as substrate consumption and product formation rates revealed the hyperproducibility of citric acid by the selected Aspergillus niger NG^GCB101 (LSD = 0.456a, HS). Case studies are highly economical because of higher yield of product, lower energy consumption and the use of raw substrate without any additional supplementation.     

Production of citric acid from sugars present in wood hemicellulose usingAspergillus niger andSaccharomycopsis lipolytica

Summary One strain each of the fungus,Aspergillus niger, and the yeast,Saccharomycopsis lipolytica, were investigated for their ability to produce citric acid from the sugars present in hemicellulose hydrolysates.S. lipolytica produced citric acid as efficiently from mannose as from glucose, but failed to assimilate xylose, arabinose or galactose.A. niger readily assimilated mannose, xylose and arabinose, and produced citric acid from these sugars although the yields were lower than from glucose. A possible inhibitory effect of arabinose on citric acid production from other sugars was observed usingA. niger.     

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.     

Mutation of Aspergillus niger for hyperproduction of citric acid from black strap molasses

Spore suspensions of Aspergillus niger GCB 75, which produced 31.1 g/l citric acid from 15% sugars in molasses, were subjected to u.v.-induced mutagenesis. Among three variants, GCM 45 was found to be the best citric acid producer and was further improved by chemical mutagenesis using NTG. Out of 3 deoxy-D-glucose-resistant variants, GCM 7 was selected as the best mutant which produced 86.1 ± 1.5 g/l citric acid after 168 h of fermentation of potassium ferricyanide + H₂SO₄-pretreated black strap molasses (containing 150 g sugars/l) in Vogel's medium. On the basis of comparison of kinetic parameters, namely the volumetric substrate uptake rate (Q _s), and specific substrate uptake rate (q _s), the volumetric productivity, theoretical yield and specific product formation rate, it was observed that the mutants were faster growing organisms and had the ability to overproduce citric acid.     

Optimization of microbiological parameters for enhanced griseofulvin production using response surface methodology

Central composite design was used to determine the optimal levels of microbiological parameters, viz., slant age, seed age and inoculum level, for enhanced griseofulvin production by Penicillium griseofulvum MTCC 1898 and Penicillium griseofulvum MTCC 2004 in shake flask fermentation. The optimal levels of slant age, seed age and inoculum level for Penicillium griseofulvum MTCC 1898 were found to be 8.8772 days, 4.2093 days, 12% (v/v) (᷁.56 kg dry cell mass/m³) and for Penicillium griseofulvum MTCC 2004, 8.221 days, 3.4875 days and 9% (v/v) (̀.09 kg dry cell mass/m³) respectively. The yield of griseofulvin under optimal conditions was found to be 1.65 times for Penicillium griseofulvum MTCC 1898 and 1.07 times for Penicillium griseofulvum MTCC 2004 higher than that obtained using unoptimized conditions. The fermentation time for maximum production of griseofulvin by Penicillium griseofulvum MTCC 1898 and Penicillium griseofulvum MTCC 2004 decreased by 4 days and 2 days respectively.     

Effect of continuous feeding of galactose on the production of recombinant glucose oxidase using Saccharomyces cerevisiae

A recombinant strain of Saccharomyces cerevisiae harboring GOD gene originated from Aspergillus niger was used for the production of extracellular glucose oxidase. The effect of continuous galactose feeding on the induction of GAL-10 promoter was examined in a 5 l bioreactor. The highest enzyme production level (164 U cm^х) was achieved at 96 h of cultivation. The production performance was compared with the results of fed-batch cultivations carried out in the same laboratory. Continuous feeding mode was found to be less productive due to excess ethanol formation and plasmid instability.     

Optimized fed-batch fermentation of L-β-hydroxy isobutyric acid by Yarrowia lipolytica

Yarrowia lipolytica KCCM50506, which transforms isobutyric acid to L-#-hydroxy isobutyric acid (L-#-HIBA), was screened. Chemostat cultures were carried out in jar fermentors at dilution rates of 0.02 h^у to 0.12 h^у. L-#-HIBA fermentation-regulating factors were determined to be specific growth rate, and concentrations of glucose and isobutyric acid in fermentor from analysis of steady-state data. The specific productivity of L-#-HIBA increased as the specific growth rate increased, apparently as a growth-associated type of product formation. A fed-batch culture was carried out under optimum conditions where the concentrations of glucose and isobutyric acid in the fermentor were maintained at 23 g l^у and 9 g l^у, respectively. The concentrations of cells and L-#-HIBA obtained at the end of fermentation were 20 g l^у and 49 g l^у, respectively, corresponding to 2.0 and 2.7 times more than concentrations in batch culture.     

Enhanced solid‐state citric acid bio‐production using apple pomace waste through surface response methodology

Aims: To evaluate the potential of apple pomace (AP) supplemented with rice husk for hyper citric acid production through solid‐state fermentation by Aspergillus niger NRRL‐567. Optimization of two key parameters, such as moisture content and inducer (ethanol and methanol) concentration was carried out by response surface methodology. Methods and Results: In this study, the effect of two crucial process parameters for solid‐state citric acid fermentation by A. niger using AP waste supplemented with rice husk were thoroughly investigated in Erlenmeyer flasks through response surface methodology. Moisture and methanol had significant positive effect on citric acid production by A. niger grown on AP (P < 0·05). Higher values of citric acid on AP by A. niger (342·41 g kg^?1 and 248·42 g kg^?1 dry substrate) were obtained with 75% (v/w) moisture along with two inducers [3% (v/w) methanol and 3% (v/w) ethanol] with fermentation efficiency of 93·90% and 66·42%, respectively depending upon the total carbon utilized after 144 h of incubation period. With the same optimized parameters, conventional tray fermentation was conducted. The citric acid concentration of 187·96 g kg^?1 dry substrate with 3% (v/w) ethanol and 303·34 g kg^?1 dry substrate with 3% (v/w) methanol were achieved representing fermentation efficiency of 50·80% and 82·89% in tray fermentation depending upon carbon utilization after 120 h of incubation period. Conclusions: Apple pomace proved to be the promising substrate for the hyper production of citric acid through solid‐state tray fermentation, which is an economical technique and does not require any sophisticated instrumentation. Significance and Impact of the Study: The study established that the utilization of agro‐industrial wastes have positive repercussions on the economy and will help to meet the increasing demands of citric acid and moreover will help to alleviate the environmental problems resulting from the disposal of agro‐industrial wastes.     

Optimisation of lignin peroxidase production from Phanerochaete chrysosporium using response surface methodology

The ligninolytic white rot fungus Phanerochaete chrysosporium, holds good promise as a biological treatment tool due to its ability to produce the lignin peroxidase enzyme which has the potential to degrade a wide variety of hazardous compounds. The effective application of this technique requires optimisation of the process variables to maximise the enzyme production. Response surface methodology was applied to determine the effects of glucose, ammonium tartarate and ferrous sulphate and their mutual interactions on lignin peroxidase production. With a view to simultaneously reducing the number of experiments and obtaining more information on the mutual interactions between the variables, a 2³ full-factorial central composite experimental design was adopted. The experimental data were fitted to a second order polynomial equation using multiple regression analysis and also analysed by appropriate statistical methods. Solving the regression equation using the multi-stage monte-carlo optimisation techniques, the optimum process conditions for enhanced production of lignin peroxidase were obtained as: glucose 0.9728 kg/m³, ammonium tartarate 0.288 kg/m³, and ferrous sulphate 0.097 kg/m³.     

Apple pomace: A potential substrate for citric acid production by Aspergillus niger

Summary Apple pomace was used as a fsubstrate for citric acid production by five strains of Aspergillus niger. A. niger NRRL 567 produced the greatest amount of citric acid from apple pomace in the presence of 4% methanol. The yield was 88% based on the amount of sugar consumed.     

Citric acid production from beet molasses by cell recycle ofAspergillus niger

Summary Production of citric acid from beet molasses at a varying pH profile using cell recycle ofAspergillus niger was investigated. Best results in terms of citric acid concentration, yield, productivity and specific citric acid productivity were obtained with a substrate pH of 3.0.     

Citric acid production from sugar cane molasses by 2-deoxyglucose-resistant mutant strain ofAspergillus niger

Citric acid production from sugar cane molasses byAspergillus niger NIAB 280 was studied in a batch cultivation process. A maximum of 90 g/L total sugar was utilized in citric acid production medium. From the parental strainA. niger, mutant strains showing resistance to 2-deoxyglucose in Vogal's medium containing molasses as a carbon source were induced by γ-irradiation. Among the new series of mutant strains, strain RP7 produced 120 g/L while the parental strain produced 80 g/L citric acid (1.5-fold improvement) from 150 g/L of molasses sugars. The period of citric acid production was shortened from 10 d for the wild-type strain to 6–7 d for the mutant strain. The efficiency of substrate uptake rate with respect to total volume substrate consumption rate,Q _s (g per L per h) and specific substrate consumption rate,q _s (g substrate per g cells per h) revealed that the mutant grew faster than its parent. This indicated that the selected mutant is insensitive to catabolite repression by higher concentrations of sugars for citric acid production. With respect to the product yield coefficient (Y _p/x), volume productivity (Q _p) and specific product yields (q _p), the mutant strain is significantly (p≤0.05) improved over the parental strain.     

The influence of type and concentration of the carbon source on production of citric acid by Aspergillus niger

Summary The influence of various carbon sources and their concentration on the production of citrate by Aspergillus niger has been investigated. The sugars maltose, sucrose, glucose, mannose and fructose (in the given order) were carbon sources giving high yields of citric acid. Optimal yields were observed at sugar concentrations of 10% (w/v), with the exception of glucose (7.5%). No citric acid was produced on media containing less than 2.5% sugar. Precultivation of A. niger on 1% sucrose and transference to a 14% concentration of various other sugars induced citrate accumulation. This could be blocked by the addition of cycloheximide, an inhibitor of de novo protein synthesis. This induction was achieved using maltose, sucrose, glucose, mannose and fructose, and also by some other carbon sources (e.g. glycerol) that gave no citric acid accumulation in direct fermentation. Precultivation of A. niger at high (14%) sucrose concentrations and subsequent transfer to the same concentrations of various other carbohydrates, normally not leading to citric acid production, led to formation of citrate. Endogenous carbon sources were also converted to citrate under these conditions. A 14%-sucrose precultivated mycelium continued producing some citrate upon transfer to 1% sugar. These results indicate that high concentrations of certain carbon sources are required for high citrate yields, because they induce the appropriate metabolic imbalance required for acidogenesis.     

Galactose inhibition of citric acid production from glucose by Aspergillus niger

Summary Previous work in this laboratory has demonstrated that although Aspergillus niger can readily utilize galactose, no citric acid is produced from this carbon source (Hossain et al. 1984). Experiments were now conducted where galactose was added at various concentrations to synthetic growth medium containing glucose as carbon source, so that the effect of galactose on citric acid production from glucose could be observed. The results showed that the presence of galactose or a product of galactose metabolism caused inhibition of citric acid production, and also reduced the rate of glucose utilization. Enzyme analyses using mycelial cell-free extracts indicated that galactose interfered with the glucose-repression of the key enzyme 2-oxoglutarate dehydrogenase.