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PubMedDate not supplied

[Metabolism of Yarrowia lipolytica grown on ethanol under conditions promoting the production of alpha-ketoglutaric and citric acids: a comparative study of the central metabolism enzymes].

A comparative study of the enzymes of the tricarboxylic acid (TCA) and glyoxylate cycles in the mutant Yarrowia lipolytica strain N1 capable of producing alpha-ketoglutaric acid (KGA) and citric acid showed that almost all enzymes of the TCA cycle are more active under conditions promoting the production of KGA. The only exception was citrate synthase, whose activity was higher in yeast cells producing citric acid. The production of both acids was accompanied by suppression of the glyoxylate cycle enzymes. The activities of malate dehydrogenase, aconitase, NADP-dependent isocitrate dehydrogenase, and fumarase were higher in cells producing KGA than in cells producing citric acid.

Citric Acid↗
PubMed2005

Phytoextraction of copper from contaminated soil by Elsholtzia splendens as affected by EDTA, citric acid, and compost.

Phytoextraction of copper (Cu) from contaminated soils greatly depends on the metal bioavailability in the soils and metal uptake ability of the plant. In this study, the effects of chelators [ethylenediamine tetraacetic acid (EDTA), citric acid (CA)] and compost amendments on Cu phytoextraction potential by a tolerant and accumulating plant species (E. splendens) were examined in two types of contaminated soils, ie., the mined soil from Cu-mined area (MS) and a paddy soil polluted by Cu refining (PS). The results showed that EDTA application at 2.5-5.0 mmol kg(-1) increased phytoextraction of Cu by four- and eight-fold from both MS and PS, respectively, which is mainly attributed to increased H2O extractable Cu in the soil. The Cu amount extracted by the shoots of E. splendens reached 800-1000 microg Cu plant(-1) from the MS and 400-700 microg Cu plant(-1) from the PS at EDTA application rates of 2.5-5.0 mmol kg(-1). The application of CA at 5.0 mmol kg(-1) had minimal effects on Cu extractability in both soils and slightly decreased Cu extraction efficiency by E. splendens. Plant biomass production was enhanced by CA at 0.25 mmol L(-1) in nutrient solution, but inhibited by CA at 5.0 mmol kg(-1) in both MS and PS. Increasing the compost rate significantly decreased H2O extractable Cu in the MS, but raised H2O-extractable Cu in the PS, which resulted mainly front the reduced exchangeable Cu in the MS and the increased exchangeable and organic fractions of Cu in the PS by compost. At high compost rate (5%), the shoots of E. splendens extracted 3.6-fold higher Cu from the PS than from the MS. These results indicate that, among the soil amendments, efficiency of Cu phytoextraction is enhanced mostly by 2.5-5.0 mmol kg(-1) EDTA, followed by 5% (w:w) compost, whereas < 5.0 mmol kg(-1) CA has minimal effects on Cu phytoextraction by E. splendens in the PS. As for the MS, only 2.5-5.0 mmol kg(-1) EDTA can elevate the efficiency of Cu, while 5% compost amendment and < 5.0 mmol kg(-1) CA application have no marked effects on Cu phytoextraction by E. splendens.

Agriculture↗
PubMed2005

Effect of different organic acids (citric, malic and ascorbic) on intragastric urease activity.

BACKGROUND: The mechanism of citric acid-enhanced Helicobacter pylori urease activity remains unclear. AIM: To compare ascorbic, citric and malic acid given at the same concentration and pH on intragastric urease activity. METHODS: Volunteers received 40 mg of famotidine the evening prior to breath testing. After an overnight fast volunteers were randomized to receive 100 mL of water or 100 mm citric, malic, or ascorbic acid, pH 2.3 containing 75 mg of 13C-urea. At 15 min a second 100 mL solution of one of the test solutions was taken without added urea. RESULTS: Twelve volunteers were studied (eight men, four women, age 19-57, median 50.7) in a randomized-crossover study. The mean breath test result at 30 min with ascorbic (17.5 +/- 5), malic (25.8 +/- 5) and citric acid (29.5 +/- 5) were all significantly greater than with water (9.5 +/- 3). Citric and malic acid were similar (P = 0.699) and significantly greater than ascorbic acid (P < 0.02). When the ascorbic acid was followed by citric acid, the result was similar to that with citrate alone (25.8 +/- 4) and greater than with ascorbic then ascorbic (P = 0.026). CONCLUSIONS: Enhancement of H. pylori urease activity is not strictly a function of the pH. We propose the effect is related to differential effects of the availability of nickel, which is required for urease activity. Citric acid and malic acid were essentially equivalent such that malic acid could substitute for citric acid in the UBT; ascorbic acid would be a poor choice.

Adult↗
PubMed1995

Salivary clearance of citric acid after an oral rinse.

OBJECTIVES: Citric acid clearance from the oral cavity may be an important factor in the erosion of dental enamel. The aim of the present study was to investigate the clearance pattern of citric acid in normal subjects. METHODS: After determination of the unstimulated salivary flow rate and the residual volume of saliva after normal swallowing, 12 subjects rinsed with 95.2 mmol l-1 citric acid for 5 s. At 1, 2, 5, 10 and 15 min after the rinse a small saliva sample was collected and the concentration of citric acid was determined enzymatically. For each subject three separate experiments on different occasions were performed with a citric acid solution of pH 2.1 and one experiment with a solution of pH 4.5. RESULTS: The salivary citric acid concentration declined biphasically: rapidly during the first 2 min, then more slowly. The elimination rate over the first minute was on average 87.7 mmol l-1 min-1 at pH 2.1 compared with 85.0 mmol l-1 min-1 at pH 4.5. The difference between individuals estimated from the areas under the clearance curve was strongly significant (P < 0.001). No significant relation was found neither between salivary flow rate and clearance, nor between residual volume after swallowing and clearance. CONCLUSION: The clearance pattern of citric acid is an individual property.

Adult↗
PubMed1991

Relationship between the stimulation of citric acid cycle oxidation and the stimulation of fatty acid esterification and inhibition of ketogenesis by lactate in isolated rat hepatocytes.

Isolated hepatocytes from fasted rats were used to study the effects of lactate on palmitate metabolism. Lactate was found to stimulate fatty acid esterification and citric acid cycle oxidation and to inhibit ketone body synthesis. These effects of lactate were largely maintained when gluconeogenesis was inhibited with either quinolinate or perfluorosuccinate, but were overcome by alpha-cyano-4-hydroxycinnamate. However, the responses of hepatocytes to lactate could be restored in the presence of alpha-cyano-4-hydroxycinnamate by the further addition of propionate. The stimulation of triacylglycerol synthesis by lactate was not associated with an increase in the concentration of glycerol 3-phosphate. Rather, there was a correlation between flux through the citric acid cycle and the rate of triacylglycerol synthesis. In all instances reduction of ketone body formation in the presence of lactate was accompanied by a stimulation of citric acid cycle oxidation.

Animals↗
PubMed2006

Inhibition of Listeria innocua in hummus by a combination of nisin and citric acid.

The effect of nisin or citric acid or combinations of these two inhibitors on the inactivation of a cocktail of three Listeria innocua strains was investigated in a model brain heart infusion (BHI) broth and hummus (chickpea dip). In BHI broth, citric acid had a limited ability to inhibit L. innocua growth. Nisin initially reduced L. innocua concentrations by about 3 log cycles; however, L. innocua reached concentrations similar to those of the control after 5 days at 22 degrees C. In combination, the effects of 500 IU/ml nisin and 0.2% citric acid were synergistic and resulted in complete elimination of L. innocua in the BHI broth. The inhibition of L. innocua by nisin (500 or 1,000 IU/g), citric acid (0.1, 0.2, or 0.3%), or their combinations also was evaluated in hummus. Citric acid alone did not affect L. innocua growth or the aerobic bacterial plate count. A combination of 1,000 IU/g nisin and 0.3% citric acid was somewhat effective (approximately 1.5-log reduction) in controlling the concentration of L. innocua and the aerobic plate count for up to 6 days. This combination also may be useful, in addition to proper hygienic practices, for minimizing the growth of the pathogen Listeria monocytogenes in hummus.

Anti-Bacterial Agents↗
PubMed2006

Acidity adjustment of HZSM-5 zeolites by dealumination and realumination with steaming and citric acid treatments.

This article describes a novel method for acidity adjustment of HZSM-5 zeolites with steaming and citric acid treatments and demonstrates the realumination effect of citric acid on HZSM-5 zeolites dealuminated by steaming. A series of modified HZSM-5 zeolites were prepared by streaming and/or acid treatments and characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), (27)Al MAS NMR spectroscopy, hydroxyl infrared spectroscopy (OH-IR), pyridine-adsorbed infrared spectroscopy, and N(2) adsorption in the present investigation. The results showed that compared with single HCl or citric acid treatment, steaming treatment, and steaming/HCl treatments, citric acid treatment after steaming exclusively increased the amount of framework Al due to reinsertion of extraframework Al into the defective sites of the steamed HZSM-5 framework. This realumination effect of the citric acid treatment on the steamed HZSM-5 zeolite, which is reported here for the first time to the best of our knowledge, could nearly recover the pore structure of the steamed zeolite to that of the parent HZSM-5 zeolite and appropriately tailor the amount and strength of different acid sites, which sheds light on optimizing the physicochemical properties of HZSM-5 zeolites. It was also found that the steaming treatment prior to the citric acid treatment was the precondition of the realumination of HZSM-5 zeolites, suggesting that the lattice defect sites generated during steaming were necessary for citric acid to work.

Journal Article↗
PubMed1983

Assessment of antitussive effects by citric acid threshold.

The cough threshold to citric acid inhalation was measured in eight subjects by single inhalations of increasing concentrations of citric acid until a cough was consistently produced. The cough threshold was measured before and after 60 mg glaucine, 60 mg codeine and matched placebo on three separate days a week apart. Base-line cough threshold in each subject was consistent from week to week. Codeine increased the threshold by more than one citric acid concentration in three subjects. Placebo and glaucine did not produce a threshold change of more than one citric acid concentration. We conclude that the citric acid threshold is a simple measure of antitussive activity. No such activity was found with glaucine.

Adult↗