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PubMed2005

Effective uptake of decontaminating agent (citric acid) from aqueous solution by mesoporous and microporous materials: an adsorption process.

The presence of citric acid in decontamination waste can cause complexation of the radioactive cations resulting in interferences in their removal by various treatment processes such as chemical precipitation, ion-exchange, etc., which are employed for the removal of radioactivity and may cause potential danger to the environment. Mesoporous Al-MCM-41 (Si/Al=30, 51, 72 and 97) and Si-MCM-41 molecular sieves were synthesized hydrothermally and characterized by XRD, BET (surface area) and FT-IR to evaluate the removal of citric acid through an adsorption process. Adsorption of citric acid over Al-MCM-41 shows the applicability of Freundlich and Langmuir isotherm and follows first order kinetics. The effects of contact time, concentration of citric acid, adsorbents (various Si/Al ratios of Al-MCM-41, Si-MCM-41, Hbeta zeolite and commercial carbon) and pH have been investigated. It has been found that the amount of citric acid adsorbed per unit gram of catalyst followed the order Al-MCM-41 (Si/Al=30)>Al-MCM-41 (Si/Al=51)>activated charcoal>Al-MCM-41 (Si/Al=72)>Al-MCM-41 (Si/Al=97)>Si-MCM-41>Hbeta zeolite.

Adsorption↗

PubMed1980

[Citric acid excretion in stone-formers and healthy controls on normal and standard diet (author's transl)].

The citric acid excretion and concentration in 24 hours urine was measured in 70 stone-formers and 16 normal subjects (controls) on normal food intake followed by 9 days on a standard diet. On days 9 and 10 on the standard diet urine was collected in 3 hours portions and citric acid and calcium was measured. From day 7 to day 10 on standard diet we found only a slight change in the 24-hour excretion of citric acid ("steady state"). The citric acid excretion and concentration is significantly lower in stone-formers than in healthy controls. In both groups there is a sinusoid rhythm in citric acid excretion and concentration throughout the 24 hour period. The calcium concentration is at its maximum when the citric acid concentration is at its minimum.

Calcium↗

PubMed2000

Production of citric acid from starch-hydrolysate by Aspergillus niger.

The present investigation explored the possible use of a rarely used agro-industrial by-product, maize starch-hydrolysate, for economic production of citric acid. To achieve this, seventeen strains of Aspergillus niger were screened for their capacity to produce citric acid using starch-hydrolysate as a substrate. The most efficient strain, ITCC-605 was selected for further improvement in citric acid content by mutation. Mutants developed by treatment with EMS and UV, singly and in combination, produced citric acid in the range of 0.51-64.7 g kg(-1) of glucose consumed. The mutant UE-1 produced the maximum citric acid which was about 130 times more than that produced by the parent strain, ITCC-605. For further increase in citric acid production from this substrate, the cultural conditions were optimized: concentration of starch-hydrolysate, 15% (glucose equivalent); ammonium nitrate, 0.25%; KH2PO4, 0.15%; nicotinic acid, 0.0001% and initial pH of 2.0. Under these conditions, the mutant strain UE-1 yielded 490 g citric acid kg(-1) of glucose consumed in 8 days of incubation at 30 degrees C. The productivity of 341 mgl(-1)h(-1) corresponded to 49% substrate conversion to citric acid.

Aspergillus niger↗

PubMed1993

Responses of single hamster parabrachial neurons to binary taste mixtures of citric acid with sucrose or NaCl.

1. Although taste experience generally arises from a mixture of gustatory stimuli, most neurophysiological studies of the mammalian central gustatory system have focused on responses to single chemical stimuli. Recently, in a study of single third-order neurons in the hamster parabrachial nucleus (PbN), we reported that mixture suppression occurs in the responses to binary mixtures of sucrose and QHCl presented to the anterior tongue. Mixture suppression was reflected both in reduced response frequencies and in an altered pattern of responses across neurons. In the current report we extend our investigation of CNS neuron responses to binary mixtures of heterogeneous stimuli to include sucrose+citric acid mixtures and NaCl+citric acid mixtures. The response to each mixture was compared with the response to the more effective component (MEC) presented alone, and those that differed by more than a selected criterion (based on response variability) were identified. 2. For all mixture responses recorded, 29% (79/256) involved mixture suppression (mixture response < MEC response), only 6% (18/276) were greater than the response to MEC, and 65% (179/276) did not differ from the response to the MEC. 3. In Experiments 1 and 2, neurons were tested with four concentrations of sucrose or citric acid each presented alone and in binary mixtures with a single strong concentration of the other stimulus. Sucrose suppression (mixture response < sucrose response) occurred in 24% of mixture responses and was exhibited almost exclusively by sucrose-best neurons, primarily to the mixtures that contained the stronger sucrose and citric acid concentrations. Sucrose suppression involved a 40% reduction of mixture response frequencies compared with responses to the sucrose component alone. 4. In Experiments 3 and 4, neurons were tested with four concentrations of NaCl or citric acid each presented alone and in binary mixtures with a single strong concentration of the other stimulus. NaCl suppression (mixture response < NaCl response) occurred in 21% of mixture responses and was displayed by both sucrose-best and NaCl-best neurons. NaCl suppression involved a 28% reduction in mixture response frequencies compared with responses to the NaCl component alone. In all experiments citric acid suppression (mixture response < citric acid response) was observed in only 6% of mixture responses and was relatively small in magnitude. 5. The across-neuron patterns (ANPs) of taste responses, which are correlated with behavioral measures of taste similarity, were compared for mixtures and components.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1992

The effect of citric acid application on periodontally involved root surfaces. 1. An in vitro light microscopic study.

This study investigated the effect of citric acid application on periodontally involved root surfaces. Forty periodontally involved teeth were randomly divided into four groups of ten teeth each: no treatment, citric acid treatment, root planing alone, and root planing in conjunction with citric acid treatment. Ten nondiseased, untreated teeth served as controls. After treatment, each tooth was split along its long axis; half was examined under light microscopy and half under scanning electron microscopy (part II of the paper). Light microscopy revealed that the effects obtained by scaling and root planing were not altered after citric acid application. Moreover, the cementum layer was not entirely removed without careful and thorough planing of the root surface. Citric acid application alone had no effect on the diseased root surface. Citric acid did not penetrate the dentinal tubules, nor did it alter the collagen content of the roots obtained by scaling and root planing.

Analysis of Variance↗

PubMed1993

Effect of palmitate concentration on the relative contributions of the beta-oxidation pathway and citric acid cycle to total O2 consumption of isolated rat hepatocytes.

The relative contributions of beta-oxidation and citric acid cycle activity to total O2 consumption during fatty acid oxidation were examined in isolated hepatocytes. When hepatocytes were incubated with palmitate alone, a rise in fatty acid concentration induced an increase in O2 uptake that reflected a large stimulation of beta-oxidation and an accompanying smaller inhibition of citric acid cycle oxidation. In the presence of lactate, successive increments in palmitate concentration over the range from 0 to 1.0 mM stimulated glucose synthesis and brought about a concomitant incremental stimulation of both beta-oxidation and citric acid cycle flux. However, above 1.5 mM palmitate, additional increments in fatty acid concentration depressed gluconeogenesis and citric acid cycle activity but induced a further stimulation of beta-oxidation. These findings demonstrate that, during fatty acid oxidation, the rate of citric acid cycle turnover is more closely linked to the rate of glucose synthesis than is the rate of beta-oxidation. This may be relevant to observations that the stimulation of hepatic O2 consumption, induced by fatty acid oxidation, is much greater than can be explained in terms of the ATP-demand arising from exposure of hepatocytes to fatty acid.

Adenosine Triphosphate↗

PubMed2003

Efficacy of various concentrations of citric acid at different pH values for smear layer removal.

OBJECTIVE: The efficacy of various concentrations of citric acid at different pH values for the removal of the superficial smear layer from dentinal surfaces was examined through the use of scanning electron microscopy. Study design Fifty extracted teeth were irrigated with sodium hypochlorite (NaOCl) during instrumentation. Citric acid solutions at 50%, 25%, 10%, and 5% (wt/vol) concentrations were prepared. In addition, similar solutions of citric acid were buffered to pH 6. Citric acid solutions with original and buffered pH values were used as final rinses. Bidistilled water and NaOCl were used as controls. The data were analyzed by using nonparametric Kruskal-Wallis and Mann-Whitney U tests. RESULTS: Lower concentrations with lower pH values removed smear layer more efficiently than the ones with higher pH values (P <.05), whereas no significant differences for higher concentrations were detected between low and high pH values. However, more destruction of peritubular dentin was observed at higher concentrations with low pH values. CONCLUSION: Within the limits of this study, lower concentrations of citric acid with its original pH were found to be as effective as higher concentrations in the removal of superficial smear layer.

Buffers↗

PubMed2004

The effect of citric acid added to hydroxypropyl methylcellulose (HPMC) matrix tablets on the release profile of vinpocetine.

Vinpocetine is a pH-dependent experimental drug with a short half-life. The sustained-release matrix tablets of vinpocetine were prepared by direct compression using hydroxypropyl methylcellulose (HPMC) and different amounts of citric acid to set up a system bringing about gradual release of this drug. In order to investigate the influence of citric acid and the pH value of medium on the drug release from HPMC matrix tablets, an in vitro release test was carried out in either phosphate buffer pH 6.8 [0.5% sodium dodecyl sulfate (SDS)] for 12 hr or in 0.1 N HCl (0.5% SDS) (0-2 hr) and phosphate buffer pH 6.8 (0.5% SDS) (2-12 hr). Dissolution curves were described by the Peppas equation: M(t)/M(inf)=ktn, and the influence of citric acid on the dissolution mechanism was estimated according to the regression parameter-n and k values. The addition of citric acid and the pH value of medium could notably influence the dissolution behavior and mechanism of drug-release from matrices. Increasing the amounts of citric acid produced an increase in drug release rate, which showed a good linear relationship between contents of citric acid and drug accumulate release (%) in phosphate buffer pH 6.8 (0.5% SDS) (r>0.99). Moreover, a higher drug release rate could be found in 0.1 N HCl (0.5% SDS) than that in phosphate buffer pH 6.8 (0.5% SDS) during the first two hours when the content of citric acid added to matrices was lower than 45 mg/tab., but no significant difference could be found when the content of citric acid was above that value. Increasing amounts of citric acid produced decreasing values of n and increasing values of k, in a linear relationship, which indicated there was a trend favoring the mechanism of diffusion with the addition of increasing quantities of citric acid.

Buffers↗

PubMed2006

Effect of microbial phytase and citric acid on phosphorus bioavailability, apparent metabolizable energy, and amino acid digestibility in distillers dried grains with solubles in chicks.

Three experiments were conducted to evaluate the effectiveness of OptiPhos phytase and citric acid for releasing the P that is not bioavailable in distillers dried grains with solubles (DDGS). The effect of OptiPhos phytate on AME(n) and amino acid digestibility was also determined. New Hampshire x Columbian chicks were fed experimental diets from 8 to 21 d of age. For Experiment 1, a basal P-deficient diet contained 40% DDGS plus supplemental amino acids, and DDGS was the only source of P. The basal diet was then supplemented with 1,000 or 10,000 phytase units (FTU)/kg of OptiPhos phytase or with 0.2% of P from KH2PO4. In Experiment 2, a slope-ratio chick growth and tibia ash assay used a P-deficient soybean meal basal diet, and it was found that the bioavailability of P in DDGS was 67%. For Experiment 3, a P-deficient basal diet with 30% DDGS plus supplemental amino acids was supplemented with 0.05 or 0.1% P from KH2PO4, with 3% citric acid, or with 1,000 or 10,000 FTU/kg of OptiPhos phytase. In Experiment 1, both 1,000 and 10,000 FTU/kg of phytase increased tibia ash but had no effect on AME(n). Both 10,000 phytase units (FTU)/kg of phytase and supplemental P increased digestibility of amino acids. In Experiment 3, supplemental phytase and citric acid increased tibia ash (mg/tibia), and it was estimated that phytase and citric acid could release from 0.04 to 0.07% P from DDGS. In terms of bioavailability coefficients, the bioavailability of the P in DDGS was increased from 62 to 72%. These results indicate that phytase and citric acid increase the bioavailability of P in DDGS, but phytase at 1,000 FTU/kg had no consistent effect on AME(n) and amino acid digestibility.

6-Phytase↗

PubMed1999

Citric acid as the test meal for the 13C-urea breath test.

OBJECTIVE: Test meals are used in the urea breath test to slow gastric emptying and to increase the area of contact with the substrate. Recently, citric acid has been suggested as an improved liquid test meal. The mechanism is unknown and could act by delaying gastric emptying, decreasing the pH at the site of the bacteria, or both. Our aim was to evaluate the effects of citric acid test meals on urea hydrolysis in vivo, to identify the possible mechanism for enhanced urea hydrolysis, and to identify the minimum effective dose. METHODS: We compared the U.S. commercial 13C-urea breath test with four liquid test meals (200 ml of water) consisting of citric acid, ascorbic acid, sodium citrate, and glucose polymer and also after the subcutaneous administration of pentagastrin. We studied healthy volunteers with and without proven H. pylori infection (by serology and histology). 13C-urea was administered orally simultaneously with the liquid test meals or immediately after the pudding had been ingested. Breath samples were taken before and after oral administration of the 13C-urea. RESULTS: A dose response in urease activity was evident as the amount of citric acid was increased from 1 to 4 g. Citric acid at 1, 2, or 4 g produced significant increases in breath 13CO2 activity, compared with the commercial pudding (p < 0.05). Ascorbic acid (p = 0.053), subcutaneous pentagastrin (to lower pH) (p = 0.199), and glucose polymer (p = 0.03) (to delay gastric emptying) all approximately doubled breath 13CO2, compared with the commercial kit. Nevertheless, the increases were all significantly less than with the 4 g citric acid test meal. CONCLUSIONS: The data are consistent with the marked effect of citric acid on gastric emptying and, possibly, distribution of the urea within the stomach being largely responsible for the enhanced urease activity with citric acid test meals. It should be possible to use a low dose of citric acid (e.g., 1 g per 200 ml) to enhance the simplicity and palatability of the test.

Ascorbic Acid↗

PubMed1999

Iron-dependent changes in cellular energy metabolism: influence on citric acid cycle and oxidative phosphorylation.

Iron modulates the expression of the critical citric acid cycle enzyme aconitase via a translational mechanism involving iron regulatory proteins. Thus, the present study was undertaken to investigate the consequences of iron perturbation on citric acid cycle activity, oxidative phosphorylation and mitochondrial respiration in the human cell line K-562. In agreement with previous data iron increases the activity of mitochondrial aconitase while it is reduced upon addition of the iron chelator desferrioxamine (DFO). Interestingly, iron also positively affects three other citric acid cycle enzymes, namely citrate synthase, isocitric dehydrogenase, and succinate dehydrogenase, while DFO decreases the activity of these enzymes. Consequently, iron supplementation results in increased formation of reducing equivalents (NADH) by the citric acid cycle, and thus in increased mitochondrial oxygen consumption and ATP formation via oxidative phosphorylation as shown herein. This in turn leads to downregulation of glucose utilization. In contrast, all these metabolic pathways are reduced upon iron depletion, and thus glycolysis and lactate formation are significantly increased in order to compensate for the decrease in ATP production via oxidative phosphorylation in the presence of DFO. Our results point to a complex interaction between iron homeostasis, oxygen supply and cellular energy metabolism in human cells.

Aconitate Hydratase↗

PubMed1981

Improved assay for mixtures of citrate and citric acid in systemic alkalizer solutions.

A modification of the USP method for the assay of systemic alkalizer solutions containing mixtures of citrate and citric acid is presented; it involves two titrations and ion-exchange chromatography. A diluted sample is tritiated with 0.02 N NaOH to find the free citric acid content. The eluate from cation-exchange chromatography of an equal volume of diluted sample is titrated with 0.02 N NaOH to assay for total citric acid. Subtracting the results of the first titration from the second provides the citrate content. Synthetic mixtures of potassium citrate-citric acid, potassium citrate-sodium citrate-citric acid, and sodium citrate-citric acid were prepared and assayed. The method was applied to commercially available preparations. The proposed method eliminates some significant errors of the compendial method, and the accuracy and reproducibility are equal or better than those obtained with the compendial method. Theoretically, the result obtained by the compendial method does not necessarily give the citrate content.

Chromatography, Ion Exchange↗

PubMed1992

Microbial production of citric acid from salad oil.

Strain CCU-U2-N4-41 was derived from a wild strain of yeast CCU-087. This strain can produce large amounts of citric acid from salad oil. The optimal medium for citric acid production is one liter of medium containing salad oil 100 g, yeast extract 2.0 g, CH3COONH4 3.0 g, KH2PO4 5.0 g, MgSO4 500 ppm, 1 ppm each of MnSO(4).5 H2O and CuSO(4).2 H2O, pH: 7.0. The optimal culture conditions are: temperature: 28 degrees C; agitation: 110 rpm; 100 mL medium in 500-mL Hinton flask; 1.5% CaCO3 added after 12 hr incubation. With 96 hr cultivation 71.2 g/L of citric acid can be produced. Citric acid produced was compared with authentic citric acid by melting point determination, IR, NMR and Mass. From the spectra, it was found that they were identical.

Citrates↗

PubMed2004

Ram horn peptone as a source of citric acid production by Aspergillus niger, with a process.

The present study deals with the production of citric acid from a ram horn peptone (RHP) by Aspergillus niger NRRL 330. A medium from RHP and a control medium (CM) were compared for citric acid production using A. niger in a batch culture. For this purpose, first, RHP was produced. Ram horns were hydrolyzed by treatment with acids (6 N H(2)SO(4), 6 N HCl) and neutralizing solutions. The amounts of protein, nitrogen, ash, some minerals, total sugars, total lipids and amino acids of the RHP were determined. RHP was compared with peptones with a bacto-tryptone from casein and other peptones. The results from RHP were similar to those of standard peptones. The optimal concentration of RHP for the production of citric acid was found to be 4% (w/w). A medium prepared from 4% RHP was termed ram horn peptone medium (RHPM). In comparison with CM, the content of citric acid in RHPM broth (84 g/l) over 6 days was 35% higher than that in CM broth (62 g/l). These results show that citric acid can be produced efficiently by A. niger from ram horn.

Animals↗

PubMed1999

Oxalic acid production by Aspergillus niger: an oxalate-non-producing mutant produces citric acid at pH 5 and in the presence of manganese.

The external pH appeared to be the main factor governing oxalic acid production by Aspergillus niger. A glucose-oxidase-negative mutant produced substantial amounts of oxalic acid as long as the pH of the culture was 3 or higher. When pH was decreased below 2, no oxalic acid was formed. The activity of oxaloacetate acetylhydrolase (OAH), the enzyme believed to be responsible for oxalate formation in A. niger, correlated with oxalate production. OAH was purified from A. niger and characterized. OAH cleaves oxaloacetate to oxalate and acetate, but A. niger never accumulated any acetate in the culture broth. Since an A. niger acuA mutant, which lacks acetyl-CoA synthase, did produce some acetate, wild-type A. niger is apparently able to catabolize acetate sufficiently fast to prevent its production. An A. niger mutant, prtF28, previously isolated in a screen for strains deficient in extracellular protease expression, was shown here to be oxalate non-producing. The prtF28 mutant lacked OAH, implying that OAH is the only enzyme involved in oxalate production in A. niger. In a traditional citric acid fermentation low pH and absence of Mn2+ are prerequisites. Remarkably, a strain lacking both glucose oxidase (goxC) and OAH (prtF) produced citric acid from sugar substrates in a regular synthetic medium at pH 5 and under these conditions production was completely insensitive to Mn2+.

Acetate-CoA Ligase↗

PubMed2005

Fate and role of ammonium ions during fermentation of citric acid by Aspergillus niger.

Stoichiometric modeling of the early stages of the citric acid fermentation process by Aspergillus niger revealed that ammonium ions combine with a carbon-containing metabolite inside the cell, in a ratio 1:1, to form a nitrogen compound which is then excreted by the mycelium. High-performance liquid chromatography analysis identified glucosamine as the product of the relationship between glucose and ammonium during the early stages of the citric acid fermentation process. Slightly acidic internal pHs, extremely low ammonium ion concentrations inside the cell, and glucosamine synthesis come into direct contradiction with the earlier theory of the ammonium pool inside the cell, regarded as responsible for inhibition of the enzyme phosphofructokinase. At later fermentation stages, when the mycelium is involved in a process of fragmentation and regrowth, the addition of ammonium sulfate leads to a series of events: the formation and secretion of glucosamine in elevated amounts, the short inhibition of citrate synthesis, growth enhancement, the utilization of glucosamine, and finally, the enhancement of citric acid production rates. Obviously, the enzymatic processes underlining the phenomena need to be reexamined. As a by-product of the citric acid fermentation, glucosamine is reported for the first time here. Suitable process manipulations of the system described in this work could lead to successful glucosamine recovery at the point of its highest yield before degradation by the fungus occurs.

Aspergillus niger↗

PubMed2004

Effects of citric acid on the viscoelasticity of cornstarch pastes.

The effects of citric acid on the rheological properties of cornstarch pastes were studied by steady shear and dynamic oscillatory viscoelasticity, intrinsic viscosity measurements and microscopic observation. The pH of cornstarch dispersion was adjusted between 6.0 and 3.0. The viscosity of the pastes was increased by lowering the pH (between 5.5 and 3.6), while the viscosity of samples with pH below 3.5 decreased further than that of the control (pH = 6.3). Citric acid promoted the collapse of starch granules; however, adding excessive citric acid led to the hydrolysis of glucose chains. No decrease in the viscoelasticity was observed for cornstarch pastes by adding acid at 25 degrees C after gelatinization.

Citric Acid↗

PubMed1979

[Fructose and citric acid content in the sperm of stud males with forms of impotencia generandi].

Fructose and citric acid content was investigated in the sperm of 27 bulls with anamnesis data for "low quality sperm". The bulls were used as breeding males in various stations for artificial insemination. Three forms of Imp. generandi are described and several grades of Oligokinospermia are differentiated. Changes in fructose and citric acid quantity differed in degree in the various forms of Imp. generandi described. Fructose and citric acid value in I and II grade Oligokinospermia were insignificantly lower than the low limit of these indices observed in bulls with normal spermoproduction. Correlation between the changes observed is positive, slight, insignificant or entirely missing. Fructose content is insignificantly lower in cases of III and IV grade Oligokinospermia and in Akinospermia, while citric acid content is reduced only in Akinospermia. The correlation between the changes is positive , high and significant. Fructose reduction in bull's semen below 400.0 mg% and of citric acid below 500.0 mg% in case of negative data for inflammatory changes in vesiculae seminalis is a diagnostic symptom for disfunction of vesiculae seminalis. More considerable changes occur in fructose values.

Animals↗