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At least 37 records · Page 2Linked to original sources
PubMed2005

Inhibition of aluminum oxyhydroxide precipitation with citric acid.

Citric acid has been shown to act as an agent for increasing the solubility of aluminum oxyhydroxides in aqueous solutions of high (>2.47 mol/mol) hydroxide-to-aluminum ratios. Conversely, citric acid also colloidally stabilizes particles in aqueous suspensions of aluminum-containing particles. Solutions of aluminum chloride, with and without citric acid added, were titrated with NaOH(aq). The presence and size of particles were determined using quasi-elastic light scattering. In solutions that contained no citric acid, particles formed instantaneously when NaOH(aq) was added but these were observed to rapidly diminish in size, disappearing at OH/Al ratios below 2.5 mol/mol. When the OH/Al ratio was raised beyond 2.5 by adding more NaOH(aq), suspensions of colloidally stable particles formed. Large polycations containing 13 aluminum atoms were detected by (27)Al solution NMR in citric-acid-free solutions with OH/Al ratios slightly lower than 2.5. In comparison, adding citric acid to solutions of aluminum chloride inhibited the formation of large aluminum-containing polycations. The absence of the polycations prevents or retards the subsequent formation of particles, indicating that the polycations, when present, act as seeds to the formation of new particles. Particles did not form in solutions with a citric acid/aluminum ratio of 0.8 until sufficient NaOH(aq) was added to raise the OH/Al ratio to 3.29. By comparison, lower amounts of citric acid did not prevent particles from forming but did retard the rate of growth.

Journal Article↗
PubMed2001

Etching characteristics of dentin: effect of ferric chloride in citric acid.

Citric acid etchants with ferric chloride (10-3) promote adhesion and are effective etchants. We used atomic force microscopy (AFM) to determine the dentin etching characteristics of 10% citric acid etchant with various additions of ferric chloride. AFM was used to measure the surface recession and morphology of dentin etching for a variety of 10% citric + Fe-Cl etchants. Commercial 10-3 was used as the control. Dentin disks were prepared and partially masked during etching so that the unetched dentin served as a reference. AFM images of the same samples were taken at each of the seven experimental steps using 10% citric acid with various quantities of ferric chloride ranging from 0 to 3% (denoted 10-0, 10-1, 10-1.8 and 10-3, respectively) which altered the pH from 1.63 to 0.42. Changes in depth (nm) relative to the reference height for intertubular dentin were determined after etching 15 s; clinical air drying, rewet for 1-5 min; desiccation for 24 h; rehydration for 24 h. Differences of log(depth change) were tested with mixed effects cell mean models. Overall differences were significant (P < 0.001). Significant differences were found between etchants and the extent of collapse on drying was dependent on pH and Fe-Cl content. Following long-term rehydration, samples recovered, but those with 0 or 1% Fe-Cl did not recover as completely (P < 0.01). Etching and collapse depended on Fe-Cl content. The collapse was nearly reversed on rehydration. Ten per cent citric acid with ferric chloride did not prevent the collapse of etched dentin. Ferric chloride additions reduced pH and increased the collapse of dentin on drying for either brief or prolonged periods. Brief rewetting can reverse the effect of brief air drying. For fully desiccated samples the effect was not reversed after 30 s, but was largely or completely reversed at 24 h in solution depending on Fe-Cl content.

Acid Etching, Dental↗
PubMed2000

Effect of proteins, phytates, ascorbic acid and citric acid on dialysability of calcium, iron, zinc and copper in soy-based infant formulas.

The possible effect of ascorbic acid, citric acid, proteins and phytate on dialysability of Ca, Fe, Zn and Cu in soy-based infant formulas is studied, taking dialysability as a measure of the amount of element available for absorption. Different dialysis percentages for similar element contents in different formulas are found. A regression analysis was applied between Ca, Zn, Cu and Fe dialysis percentages and soy-based formula components to estimate the possible influence of the latter on the dialysability of the elements. Significant correlations were found between citric acid contents and dialysability of Zn and Fe. No correlations were found between protein, ascorbic acid and phytic acid contents and the dialysis percentages of the four minerals. However, we must to point out that the range of protein contents was narrow and the ascorbic acid: iron ratio was high in our formulas.

Ascorbic Acid↗
PubMed1983

[Influence of picolinic acid and citric acid on intestinal absorption of zinc in vitro and in vivo].

The influence of the ligands picolinic acid and citric acid on the intestinal absorption of zinc was studied in two different experimental trials with Zn-depleted and Zn-supplied pair-fed rats using everted sacs in vitro and the ligated small intestine in vivo. ZnSO4 was applied in water solution (pH 5.8) without ligands or together with picolinic acid at a molar ratio of 1:0.2, 1:2, and 1:20 or together with citric acid at a molar ratio of 1:1, 1:10, and 1:100. The intestinal Zn transfer of the Zn-depleted rats with picolinic acid is significantly increased only at a molar ratio of 1:20 (zinc:ligand) (P less than 0.001). The other in vitro results of Zn absorption were only slightly improved, mainly at the high molar excess of picolinic acid in comparison to ZnSO4 without ligands. Only a tendency for an increased Zn transfer--however, already at a narrow molar ratio of 1:1 or 1:10--could be seen when citric acid was added. The intestinal uptake was not influenced by citric acid. The absorption of zinc in vivo did not vary in dependence of the addition of picolinic or citric acid in different molar ratio in comparison to ZnSO4 addition without ligands. Zn-depleted rats showed a significantly higher Zn absorption rate than Zn supplied pair-fed rats independently of the kind of ligand and the zinc:ligand ratio (P less than 0.001). These results are discussed in detail.

Animals↗
PubMed1985

Fluorine concentration changes in human periodontally diseased tooth roots following several treatment times with citric acid.

Citric acid conditioning of exposed cementum has become an important adjunct to the clinical management of periodontal disease, and aggressive root planing is recommended to remove hypermineralized and endotoxin-laden diseased cementum. A nuclear resonance reaction technique was used to examine fluorine concentration changes subsequent to application of citric acid (pH 1.0) to the periodontal disease-exposed cementum surfaces of human tooth roots. The technique does not require the test teeth to be sectioned, thereby permitting longitudinal assessments of changes in fluorine concentration and minimizing measurement errors due to the considerable biological variation found between individuals. Initial fluorine concentrations ranged from 0.9%-2.4%, and maxima occurred within 4-6 microns of the surface, suggesting the presence of a hypermineralized layer. Within 60 sec, the citric acid had effectively removed the hypermineralized layer and the previously observed fluctuations in fluorine concentration leveled out at 0.3%-0.5%. Although the results indicated rapid removal of the hypermineralized layer and establishment of fluorine levels normally found in healthy cementum, the experimental design did not permit appraisal of potential effects upon the organic components of periodontally-exposed cementum.

Citrates↗
PubMed1995

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.

Journal Article↗
PubMed1990

[Effects of sodium chloride, acetic acid and citric acid on the dissolution of aluminum from aluminum cooking utensils].

In order to investigate the effects of sodium chloride and organic acids on aluminum elution from cooking utensils made of aluminum, the quantities of aluminum elution were measured in solutions with various concentrations of sodium chloride, acetic acid and citric acid by flameless atomic adsorption spectrophotometry. The increase of the aluminum elution rate from a pudding cup, an aluminum pan and an alumite pan could be clearly distinguished by the coexistence of acetic acid or citric acid and sodium chloride. The elution was low in the presence of sodium chloride at room temperature, but it was distinctly accelerated by heating. Although alumite treatment had the effect of protection against aluminum elution, such elution obviously increased, as shown by the existence of acid and sodium chloride at high temperatures. Aluminum elution rates from surface-untreated cooking utensils made of aluminum were increased by heating by a factor of several thousand.

Acetates↗
PubMed2005

Uranium accumulation of crop plants enhanced by citric acid.

Citric acid was applied to soil to enhance U accumulation in four crop plants. While the highest enhanced U accumulation of aboveground tissues (a.c. 2000 mg kg(-1) dry weight) occurred in the leaves of Indian mustard (Brassica juncea), the highest enhanced U accumulation of roots (a.c. 3500 mg kg(-1) dry weight) occurred in canola (Brassica napus var. napus). Uranium translocation among tissues of test plants is in the relation of roots>shoots congruent with leaves. The flowers of sunflower (Helianthus annuus) contained similar or higher U concentrations than those found in shoots, but concentrations in seeds are close to zero. In conclusion, Indian mustard is recommended as a potential species for phytoextraction for U-contaminated soil due to its high U accumulation of aboveground biomass (a.c. 2200 microg per plant). There is no evidence that two types of soils cause a significant difference of the enhanced U accumulation (p<0.05). Results, however, indicate that additional citric acid may result in downward U migration that may contaminate groundwater. Speciation of U that is taken up by plants is also discussed in the end.

Citric Acid↗
PubMed1991

The lactic acid and citric acid content in the gingival fluid of orthodontic patients.

Alveolar bone turnover has two phases: bone resorption and formation. Bone resorption entails both mineral removal and collagenolysis. A pH decrease over the local bone surface is required for mineral removal. Both lactic acid and citric acid has been suggested as the acids which remove crystals. During the orthodontic movement of teeth, a process of overall bone resorption occurs during displacement, whereas at the retention stage this process needs to be stopped in order to stabilize the alveolar bone. Thus, lactic acid and citric acid may be valid parameters of bone resorption intensity. The purpose of this investigation is firstly to test if these acids can be detected in gingival fluid around the moving teeth, and secondly to find if any changes occur before, during and after orthodontic tooth movement. The results indicate that these acids can be good parameters which show how favorably tooth movement is proceeding. They also show how stable the teeth are when orthodontic force is stopped to apply.

Adolescent↗
PubMed2003

Effect of citric acid and citric acid-sucrose mixtures on swallowing in neurogenic oropharyngeal dysphagia.

The ability of sour and sweet-sour mixtures to improve swallowing in 11 nursing home residents with neurogenic oropharyngeal dysphagia was investigated using fiberoptic endoscopic evaluation of swallowing. Citric acid (2.7%) significantly reduced aspiration and penetration compared with water. Teaspoon delivery of liquids significantly reduced aspiration and penetration compared with natural cup drinking. Subjects tended to appropriately self-regulate the cup volume they consumed after the first trial. A significant increase in spontaneous dry swallows was observed after both taste stimuli. The mechanisms for improved swallowing due to citric acid are not understood but may be due to increased gustatory and trigeminal stimulation of acid to the brainstem in neurologically impaired subjects.

Aged↗
PubMed1976

Effect of acetic and trans-aconitic acids on citric acid production by Aspergillus niger.

The effect of acetic and trans-aconitic acids on citric acid production by A. niger at different pH values was studied. The presence of acetic acid at pH 2 prevented spore germination, while it decreased the fungal growth and citric acid production at other pH values. In the presence of trans-aconitic acid the inhibition was less marked at lower than at higher pH values.

Acetates↗
PubMed1979

[Analysis of citric acid and citrates. Citric acid and urolithiasis].

In the first part the physico-chemical, analytic chemical and physiologic biochemical properties of the citric acid are discussed. In the second part the author enters the role of the citric acid in the formation of uric calculi. In the third part is reported on the individual methods of the determination of citric acid and the method practised in the author's laboratory is described.

Chemical Phenomena↗
PubMed2000

Inhibition of Aeromonas caviae and A. sobria by sodium choloride, citric acid, ascorbic acid, potassium sorbate and extracts of Thymus vulgaris.

The respective and combined effects of sodium chloride, ascorbic acid, citric acid, potassium sorbate, and Thymus vulgaris extract on the growth of Aeromonas caviae and Aeromonas sobria were investigated. Sodium chloride (3%) significantly reduced the growth and 4% NaCl inhibited growth of the tested strains. Ascorbic acid (0. 1%), potassium sorbate (0.05%), and citric acid (0.03%) slightly inhibited growth. T. vulgaris extract (0.3%) greatly reduced the growth. Various combinations of these compounds prevented growth of the tested strains. A combination of NaCl (3%) and ascorbic acid (0. 1%), citric acid (0.03%) and potassium sorbate (0.05%), or citric acid (0.03%) and ascorbic acid (0.1%) inhibited growth of A. caviae and A. sobria. In fish homogenates, the addition of ascorbic acid (0. 1%) and citric acid (0.03%) was the most effective combination tested.

Aeromonas↗
PubMed1976

Replenishment and depletion of citric acid cycle intermediates in skeletal muscle. Indication of pyruvate carboxylation.

The effects of various substrates on the concentrations of free amino acids, citric acid cycle intermediates and acylcarnitines were studies in perfused hindquarter of rat in presence of glucose and insulin in order to assess regulatory mechanisms of the level of citric acid cycle intermediates in skeletal muscle. 1. Acetate and acetoacetate effected a significant increase in the level of citrate cycle intermediates and accumulation of acetylcarnitine. These changes were accompanied by a reduction in the level of alanine. The concentration of AMP was significantly elevated. 2. Muscle mitochondria fixed 14CO2 in the presence of pyruvate. The products were identified as malate or citrate when whole and disintegrated mitochondria were used respectively. The fixation was greatly stimulated by acetylcarnitine. 3. Acetylcarnitine inhibited the production of pyruvate from malate by muscle mitochondria. 4. Perfusion with 2-oxoisocaproate and 2-oxoisovalerate promoted increases in the level of citric cycle intermediates, a drop in both alanine and glutamate, and accumulation of branched-chain acylcarnitines. 2-Oxoisocaproate also caused a reduction of alanine released from the muscle. 5. Perfusion with leucine and valine did not change the concentration of citric acid cycle intermediates, but elevated glutamate and still more the concentration of alanine. 6. It is concluded that citric cycle intermediate level in the perfused resting muscle is modified by a) conditions which change the concentration of acetyl-CoA and thereby modify the rate of pyruvate carboxylation and decarboxylation of malate via malic enzyme b) conditions which change the concentration of pyruvate cause changes in alanine and cycle intermediates in the same direction via transamination reactions c) conditions which change the concentrations of 2-oxoacids which are converted to cycle intermediates via oxidation.

Acetyl Coenzyme A↗