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PubMed1996

Simultaneous determination of oxalic and citric acids in urine by high-performance liquid chromatography.

A simple method for the simultaneous determination of oxalic and citric acids had been developed using reversed-phase HPLC. An aqueous solution containing potassium dihydrogen phosphate (0.25%) and tetrabutylammonium hydrogen sulphate (2.5 mmol) at pH 2.0 was used as mobile phase. Under these conditions both the components were well resolved and detected at 210 nm. The recovery for oxalic and citric acids was 97% and 102%, respectively. The method presented here was applied to urine specimens of a large number of urolithic patients and control subjects. Because of the simplicity of the method its application provides better means of monitoring the concentration of oxalic and citric acids in the formation of renal calculi.

Chromatography, High Pressure Liquid↗
PubMed2000

Effect of cadmium and copper on the production of citric acid by Aspergillus niger.

Copper and cadmium inhibited the growth as well as citric acid production (depending on the heavy metal concentrations) by citric-acid-producing Aspergillus niger. Activity of citrate synthase was connected with citrate synthesis in the absence as well as in the presence of heavy metals. The activity of aconitase, and both NAD- and NADP-isocitrate dehydrogenases was strongly inhibited by copper. The contents of DNA and proteins in the cells decreased but the contents of lipids and polysaccharides increased considerably in the presence of both heavy metals.

Aconitate Hydratase↗
PubMed1980

The influence of ultrasonic waves, alone and in presence of certain salts on the microbial production of citric acid by Aspergillus niger.

The influence of ultrasonic waves, alone and in presence of different (0.1, 0.5, and 1.0%) concentrations of NaCl, KH2PO4 and NH4Cl on the microbial production of citric acid by Aspergillus niger was studied. It was observed that in presence of sonic waves alone the yield of citric acid was generally better than that of control. Besides, some morphological changes in the diameter of the conidiophore of the of the mould was also noted. The effect of sonics in presence of NaCl was inconspicuous since at all sonic doses taken for the study, the yield of citric acid was less in comparison to the control. However, in presence of 0.5% KH2PO4 the yield was comparatively better (42.2%) over the control. The best result obtained amongst these treatments was found with the effect of sonics in presence of 0.5% NH4Cl in which the optimum yield of citric acid produced was greater than that of the control by 52.4%.

Ammonium Chloride↗
PubMed1982

Stability of citric acid solutions during a five month period.

The purpose of this study was to examine the effect of time, light and air exposure on the pH stability and demineralization ability of a standardized pH 1 citric acid solution. A 0.5 liter pH 1 citric acid solution was prepared and examined over a 5 month period. The results indicated that pH 1 citric acid and solutions prepared under the described conditions remained stable during the examination period with regards to all tested variables.

Air↗
PubMed2005

The extraordinary mitochondrion and unusual citric acid cycle in Trypanosoma brucei.

African trypanosomes are parasitic protozoa that cause sleeping sickness and nagana. Trypanosomes are not only of scientific interest because of their clinical importance, but also because these protozoa contain several very unusual biological features, such as their specially adapted mitochondrion and the compartmentalization of glycolytic enzymes in glycosomes. The energy metabolism of Trypanosoma brucei differs significantly from that of their hosts and changes drastically during the life cycle. Despite the presence of all citric acid cycle enzymes in procyclic insect-stage T. brucei, citric acid cycle activity is not used for energy generation. Recent investigations on the influence of substrate availability on the type of energy metabolism showed that absence of glycolytic substrates did not induce a shift from a fermentative metabolism to complete oxidation of substrates. Apparently, insect-stage T. brucei use parts of the citric acid cycle for other purposes than for complete degradation of mitochondrial substrates. Parts of the cycle are suggested to be used for (i) transport of acetyl-CoA units from the mitochondrion to the cytosol for the biosynthesis of fatty acids, (ii) degradation of proline and glutamate to succinate, (iii) generation of malate, which can then be used for gluconeogenesis. Therefore the citric acid cycle in trypanosomes does not function as a cycle.

Animals↗
PubMed1991

Antitussive effects of diphenhydramine on the citric acid aerosol-induced cough response in humans.

This controlled crossover study in twenty healthy volunteer subjects utilized the citric acid aerosol-induced cough response as a means to demonstrate the effectiveness of 25 mg of diphenhydramine as an antitussive. Entry was limited to only those subjects who manifested a consistent, quantitatively definable response to a 5% citric acid challenge. Subjects were initially dosed with either a placebo vehicle or 25 mg diphenhydramine in a 10 ml formulation. Following drug ingestion, subjects were challenged at 15, 30, 45, 60, 120, and 240 minutes. Three days later, subjects were administered the alternate treatment and rechallenged at the same time points. Diphenhydramine was effective at the earliest time point assessed, 15 minutes, and continued to be as effective over the entire 4-hour duration of the test period. For the placebo vehicle, the mean cough counts did not change significantly from baseline. Neither the putative soothing effect of a liquid formulation nor accommodation to the citric acid spray can account for all the early and consistently significant activity of diphenhydramine in suppressing the cough response. The early onset of activity of diphenhydramine may be due to its local anesthetic properties or may indicate that the dose of diphenhydramine required for effective antitussive activity is lower than that required for effective antihistaminic activity. These results require further corroboration in direct comparisons of various doses of diphenhydramine with positive controls in both this model and clinical cough counting models employing pathologic cough indices. A 25 mg dose of diphenhydramine appears to be effective as an antitussive agent.

Administration, Inhalation↗
PubMed2005

Effect of topical fluorides and citric acid on heat-pressed all-ceramic material.

The effects of citric acid and acidulated phosphate fluoride on the surface roughness of autoglazed and overglazed all-ceramic IPS Empress materials were analyzed. Atomic force microscopy was used to measure the roughness. Citric acid solution (2.00%) was applied for 8 hours, simulating 2 years of exposure. Acidulated phosphate fluoride gel (1.23%) was applied for 32 minutes, simulating 2 years of fluoride therapy. Acidulated phosphate fluoride caused a significant roughening effect on both autoglazed and overglazed specimens.

Acid Etching, Dental↗
PubMed1988

The effects of different foods and concentrations of citric acid on the flow rate of whole saliva in man.

The effects of seven different foods and three concentrations of citric acid in 16 adult subjects of each sex were evaluated. The foods were steamed rice, french fries, cheeseburger, cookie, milk chocolate, apple, and rhubarb pie. The volume of saliva was determined by subtracting the initial weight of food from that of the food bolus after subjects had chewed it normally and then spat it into a weighed container, without swallowing. The flow rates were compared with those produced in response to infusion into the mouth of 52, 156 and 260 mmol/l citric acid through a plastic tube at a constant rate of 5.0 ml/min, controlled by a peristaltic pump. Mean salivary flow rates were highest with rhubarb pie and lowest with rice; these were 70.5 +/- 11.3 and 43.2 +/- 14.4 per cent, respectively, of the maximum flow rate (7.07 +/- 2.16 ml/min) elicited by 260 mmol/l (5 per cent) citric acid. The chewing times per 10 g of food were inversely related to the water content (r = -0.82). The water content of the food bolus varied over a wide range (28-87 per cent). Thus normal foods elicit a salivary flow rate which is a high fraction of the maximum secretory rate achieved in response to acid.

Adult↗
PubMed1995

Citric acid production by Aspergillus niger in surface culture on inulin.

Aspergillus niger produces citric acid during surface fermentation on inulin, a reserve carbohydrate of plant tubers. Citric acid yields can be improved by airflow over the surface of the fermentation but yields from inulin are 20-30% lower than from sucrose, the traditional commercial substrate.

Aspergillus niger↗
PubMed1981

Age and sex effects on taste of sucrose, NaCl, citric acid and caffeine.

A procedure combining forced choice discrimination with intensity scaling served to evaluate taste perception of sucrose, NaCl, citric acid and caffeine in 24 young and 24 geriatric subjects. Each group was divided equally by sex. No overall sex differences occurred for taste discrimination, and suprathreshold taste intensity scaling for sucrose and NaCl did not differ by sex or age. However, young adults generally discriminated lower concentrations of citric acid and caffeine from water blanks than did geriatric subjects. Younger subjects judged suprathreshold concentrations of caffeine significantly more intense, as did young females compared to young males; similarly, young females judged citric acid as stronger than did older males. The present suggest that age and gender are major factors in sour and bitter perception.

Adult↗
PubMed1984

Oral absorption of chlortetracycline in turkeys: influence of citric acid and Pasteurella multocida infection.

Plasma and tissue concentrations, following the oral administration of the antibiotic chlortetracycline (CTC) alone or with citric acid, were determined in healthy and infected (Pasteurella multocida) turkeys. The principal results were: 1) The dose (of CTC) versus plasma level relationship was nearly linear. 2) Addition of citric acid to an oral preparation produced significantly higher plasma levels when divalent cations Ca2+ (.3 g/liter) and Mg2+ (.1 g/liter) were present in the drinking water and dosage solution than when citric acid was omitted. 3) The concentration of CTC was considerably higher in the liver and kidney than in the muscle and brain. 4) Birds infected with P. multocida had significantly higher plasma levels than healthy birds. 5) Oral administration of CTC increased the survival rate of the birds infected with P. multocida.

Administration, Oral↗
PubMed1998

Enzymatic Determination of Citric Acid in Honey by Using Polyvinylpolypyrrolidone Clarification.

To characterize honey types, a citric acid determination may be useful. A citric acid determination on honey was carried out with previous polyvinylpolypyrrolidone (PVPP) clarification followed by the Boehringer-Mannheim GmbH enzymatic test. The sample solution was prepared from 2 g of honey in 100 mL of Milli-Q water. A volume of 10 mL of this sample was clarified with PVPP stirring for 1 min and filtered. The enzymatic determination was measured spectrophotometrically at 340 nm, using citrate lyase, L-malate dehydrogenase, and L-lactate dehydrogenase. With these conditions, there were no observed interference effects. The proposed method improves precision [coefficient of variation (CV) between 0.26% and 1.60%] and recovery (between 98.0% and 100.9%) on the direct enzymatic analysis (% CV between 1.02 and 2.66 and recovery between 84.0% and 115.6%). Furthermore, the cost was reduced 70% using a microtest. The method was applied to 20 honeys of Galicia (northwestern Spain), and the results ranged between 44.2 and 827.0 mg of citric acid/kg of honey (mean = 192.9 mg/kg).

Journal Article↗
PubMed1985

Healing after treatment of periodontal intraosseous defects. III. Effect of osseous grafting and citric acid conditioning.

The present study was performed to determine whether the healing of periodontal intraosseous defects could be improved through the combined use of citric acid conditioning of the root surfaces and grafting of autogenous intraoral cancellous bone. 28 proximal defects in 19 patients were treated surgically including acid conditioning of the root surfaces. Another 25 defects in these patients were treated with acid conditioning combined with osseous grafts using the maxillary tuberosity areas as donor sites. Both therapies, e.g., citric acid conditioning alone and acid conditioning combined with osseous grafting resulted in approximately 1 mm gains of probing attachment and probing bone levels. Within the parameters of this study, osseous grafting did not enhance the effect of citric acid conditioning alone. Limited improvement of the treated defects of the present study was obtained in spite of the use of supplementary regenerative techniques.

Adult↗
PubMed2000

Oxidation of acetate through reactions of the citric acid cycle by Geobacter sulfurreducens in pure culture and in syntrophic coculture.

Geobacter sulfurreducens strain PCA oxidized acetate to CO2 via citric acid cycle reactions during growth with acetate plus fumarate in pure culture, and with acetate plus nitrate in coculture with Wolinella succinogenes. Acetate was activated by succinyl-CoA:acetate CoA-transferase and also via acetate kinase plus phosphotransacetylase. Citrate was formed by citrate synthase. Soluble isocitrate and malate dehydrogenases NADP+ and NAD+, respectively. Oxidation of 2-oxoglutarate was measured as benzyl viologen reduction and strictly CoA-dependent; a low activity was also observed with NADP+. Succinate dehydrogenase and fumarate ductase both were membrane-bound. Succinate oxidation was coupled to NADP+ reduction whereas fumarate reduction was coupled to NADPH and NADH Coupling of succinate oxidation to NADP+ or cytochrome(s) reduction required an ATP-dependent reversed electron transport. Net ATP synthesis proceeded exclusively through electron transport phosphorylation. During fumarate reduction, both NADPH and NADH delivered reducing equivalents into the electron transport chain, which contained a menaquinone. Overall, acetate oxidation with fumarate proceeded through an open loop of citric acid cycle reactions, excluding succinate dehydrogenase, with fumarate reductase as the key reaction for electron delivery, whereas acetate oxidation in the syntrophic coculture required the complete citric acid cycle.

Acetates↗
PubMed1987

Control of flux through the citric acid cycle and the glyoxylate bypass in Escherichia coli.

The glyoxylate bypass and citric acid cycle operate concurrently in Escherichia coli when acetate is the sole source of carbon and energy to sustain aerobic growth. The overall carbon balance allows fluxes through the central metabolic pathways (CMPs) to be computed on the assumption that these metabolic pathways are known. Acetate is fluxed via the CMPs to the precursors required for synthesis of new biomass and also to generate the reducing power and ATP required to convert these precursors to biomass. Under these circumstances, a junction is created at isocitrate where isocitrate lyase (ICL) and isocitrate dehydrogenase (ICDH) compete for their common substrate. In general, flux through ICL generates the precursors used for biosynthesis while the larger part of the flux (95%) through ICDH is dedicated to the supply of reducing power and ATP. The system sustains a large intracellular pool of isocitrate to accommodate the rather low affinity of ICL for this substrate. Excessive flux of isocitrate through ICDH is prevented by regulation of ICDH activity: reversible inactivation of ICDH is achieved by a bifunctional kinase/phosphatase, as the phosphorylated form of ICDH has no activity. The kinase/phosphatase responds to two classes of effectors--intermediates of the CMPs generated by flux through ICL and the lower energy forms of ATP and NADPH (ADP, AMP and NADP+) generated when these intermediates are used for biosynthesis. The effect is to adjust flux through ICDH so that the rate of supply of NADPH and ATP is equal to the demands of biosynthesis. Biosynthetic fluxes are limited by the rate of supply of precursors which depends on flux through ICL. Growth rate is most likely limited by the primary flux of acetate to acetyl-CoA or flux through ICL. In the steady state, the flux through ICDH is regulated to be twice the throughput of ICL. The evolution of this complex pattern of control may have depended on alternatives to the citric acid for energy generation.

Acetates↗
PubMed2002

Attempts at improving citric acid fermentation by Aspergillus niger in beet-molasses medium.

Natural oils with high unsaturated fatty acids content when added at concentrations of 2% and 4% (v/v) to beet molasses (BM) medium caused a considerable increase in citric acid yield from Aspergillus niger. The fermentation capacities were also examined for production of citric acid using BM-oil media under different fermentation conditions. Maximum citric acid yield was achieved in surface culture in the presence of 4% olive oil after 12 days incubation.

Aspergillus niger↗