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PubMed1996

Does root surface conditioning with citric acid delay healing?

Effects of topical citric acid application on tissue maturation was studied in standardized periodontal defects in 6 beagle dogs. Following elevation of facial mucoperiosteal flaps, fenestration defects, 3 mm in diameter, were made through the cortical bone and recessed 0.5 mm into the dentin of maxillary canines. 1 defect in each dog was conditioned with a saturated solution of citric acid for 3 min and then rinsed with saline. Control defects in contralateral teeth were treated with saline only for the same length of time. The defects were covered with an expanded polytetrafluoroethylene membrane and the flaps repositioned and sutured. 14 days postsurgery, healing appeared more advanced along the defect walls and floor than in the center of the defect in all instances. Histometrically, citric acid-conditioned defects exhibited a higher density of collagen fibers along the defect walls and floor and adjacent to the barrier membrane as well as more advanced resolution of the residual blood clot than the surgical controls. Differences in fibroblast density within specimen pairs were non-significant. All control defects but none of the acid-conditioned defects showed an artifactual split between the dentin walls and the granulation tissue. This study failed to support the contention that topical application of citric acid to root surfaces may delay healing following periodontal surgery.

Administration, Topical↗
PubMed2006

Application of kaolin to improve citric acid production by a thermophilic Aspergillus niger.

Citric acid production by a thermophilic strain of the filamentous fungus Aspergillus niger IIB-6 in a medium containing blackstrap cane molasses was improved by the addition of kaolin to the fermentation medium. The fermentation was run in a 7.5-l stirred bioreactor (60% working volume). The optimal sugar concentration was found to be 150 g/l. Kaolin (1.0 ml) was added to the fermentation medium to enhance volumetric production. The best results in terms of product formation were observed when 15 parts per million (ppm) kaolin was added 24 h after inoculation. With added kaolin, citric acid production was enhanced 2.34-fold, compared to a control fermentation without added kaolin. The length of incubation to attain this product yield was shortened from 168 to 96 h. The comparison of kinetic parameters showed improved citrate synthase activity of the culture (Y (p/x)=7.046 g/g). When the culture grown at various kaolin concentrations was monitored for Q (p), Q (s), and q (p), there was significant improvement in these variables over the control. Specific production by the culture (q (p)=0.073 g/g cells/h) was improved several fold. The addition of kaolin substantially improved the enthalpy (DeltaH (D)=74.5 kJ/mol) and entropy of activation (DeltaS=-174 J/mol/K) for citric acid production, free energies for transition state formation, and substrate binding for sucrose hydrolysis. The performance of fuzzy logic control of the bioreactor was found to be very promising for an improvement ( approximately 4.2-fold) in the production of citric acid (96.88 g/l), which is of value in commercial applications.

Aspergillus niger↗
PubMed1985

The pulpal response to dilute citric acid smear removers.

The aim of this study was to determine the pulpal response to three dilute citric acid smear removers. Forty-eight vervet monkeys (Cercopithecus aethiops pygerythrus), in three groups of sixteen animals provided 384 tooth specimens for the histological evaluation of the pulpal response at 3, 31, and 59 days post-operatively. Labial Class V cavities were prepared in the maxillary and mandibular incisor teeth. The pulpal responses elicited by 1% aqueous citric acid, 1% citric acid in 30% ethanol and 0.1% citric acid in 30% ethanol solutions, in unlined cavities and in cavities lined with Dycal after acid application, were compared with those elicited by a negative control material--(Nobetec), and a positive control material--(Syntrex). Using Stanley's criteria the most severe pulpal responses were seen in teeth treated with 1% aqueous citric acid and 1% citric acid in 30% ethanol without a subsequent liner, and by Syntrex at all three time intervals. The use of Dycal as a liner after smear removal markedly reduced the pulpal responses.

Acid Etching, Dental↗
PubMed1999

Bronchoconstriction induced by citric acid inhalation in guinea pigs: role of tachykinins, bradykinin, and nitric oxide.

Gastroesophageal acid reflux into the airways can trigger asthma attacks. Indeed, citric acid inhalation causes bronchoconstriction in guinea pigs, but the mechanism of this effect has not been fully clarified. We investigated the role of tachykinins, bradykinin, and nitric oxide (NO) on the citric acid- induced bronchoconstriction in anesthetized and artificially ventilated guinea pigs. Citric acid inhalation (2-20 breaths) caused a dose-dependent increase in total pulmonary resistance (RL). RL value obtained after 10 breaths of citric acid inhalation was not significantly different from the value obtained after 20 breaths (p = 0.22). The effect produced by a half-submaximum dose of citric acid (5 breaths) was halved by the bradykinin B2 receptor antagonist HOE 140 (0.1 micromol x kg-1, intravenous) and abolished by the tachykinin NK2 receptor antagonist SR 48968 (0.3 micromol x kg-1, intravenous). Bronchoconstriction induced by a submaximum dose of citric acid (10 breaths) was partially reduced by the administration of HOE 140, SR 48968, or the NK1 receptor antagonist CP-99,994 (8 micromol x kg-1, intravenous) alone and completely abolished by the combination of SR 48968 and CP-99,994. Pretreatment with the NO synthase inhibitor, L-NMMA (1 mM, 10 breaths every 5 min for 30 min) increased in an L-arginine-dependent manner the effect of citric acid inhalation on RL. HOE 140 and CP-99,994 markedly reduced the L-NMMA-potentiated bronchoconstriction to inhaled citric acid. We conclude that citric acid-induced bronchoconstriction is caused by tachykinin release from sensory nerves, which, in part, is mediated by endogenously released bradykinin. Simultaneous release of NO by citric acid inhalation counteracts tachykinin-mediated bronchoconstriction. Our study suggests a possible implication of these mechanisms in asthma associated with gastroesophageal acid reflux and a potential therapeutic role of tachykinin and bradykinin antagonists.

Administration, Inhalation↗
PubMed1996

Effect of citric acid clearance on the saturation with respect to hydroxyapatite in saliva.

Citric acid contained in beverages and foods is one of the main causes of enamel erosion. It was hypothesized that the clearance of citric acid from saliva would influence the degree of salivary saturation with respect to hydroxyapatite (OHAp). Ten subjects rinsed with 2% citric acid, pH 2.1, for 5s. Before and at 1,2, 5, 10 and 15 min after the rinse, a small saliva sample was collected. The sample pH, ionic strength and the concentrations of ionized calcium, inorganic phosphate and citric acid were determined. The pH of the saliva decreased from 7.21 + or - 0.40 (mean + or - SD) at time zero to a minimum of 6.46 + or - 0.88 at 1 min after the rinse. It was back to baseline value after 15 min. The saliva was supersaturated with respect to OHAp at time zero. After the rinse with the citric acid the saturation level shifted to undersaturation in all individuals except one. At 1 and 2 min after the rinse the saliva was, on average, undersaturated. After 5 min the average saturation level was back to supersaturation. The individual differences were large. The correlations between the rate of clearance of citric acid during the 1 minute and the minimum degree of saturation with respect to OHAp at 1,2 and 5 min after the rinse were significant (r 0.84, r 0.76 and r 0.79, respectively). In conclusion, rinsing with citric acid will cause a decrease in the saturation level with respect to OHAp in a highly individual pattern.

Adult↗
PubMed1991

Low- and high-affinity transport systems for citric acid in the yeast Candida utilis.

Citric acid-grown cells of the yeast Candida utilis induced two transport systems for citric acid, presumably a proton symport and a facilitated diffusion system for the charged and the undissociated forms of the acid, respectively. Both systems could be observed simultaneously when the transport was measured at 25 degrees C with labelled citric acid at pH 3.5 with the following kinetic parameters: for the low-affinity system, Vmax, 1.14 nmol of undissociated citric acid s-1 mg (dry weight) of cells-1, and Km, 0.59 mM undissociated acid; for the high-affinity system, Vmax, 0.38 nmol of citrate s-1 mg (dry weight) of cells-1, and Km, 0.056 mM citrate. At high pH values (above 5.0), the low-affinity system was absent or not measurable. The two transport systems exhibited different substrate specificities. Isocitric acid was a competitive inhibitor of citric acid for the high-affinity system, suggesting that these tricarboxylic acids used the same transport system, while aconitic, tricarballylic, trimesic, and hemimellitic acids were not competitive inhibitors. With respect to the low-affinity system, isocitric acid, L-lactic acid, and L-malic acid were competitive inhibitors, suggesting that all of these mono-, di-, and tricarboxylic acids used the same low-affinity transport system. The two transport systems were repressed by glucose, and as a consequence diauxic growth was observed. Both systems were inducible, and not only citric acid but also lactic acid and malic acid may induce those transport systems. The induction of both systems was not dependent on the relative concentration of the anionic form(s) and of undissociated citric acid in the culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport↗
PubMed2004

Evidence of a new role for the high-osmolarity glycerol mitogen-activated protein kinase pathway in yeast: regulating adaptation to citric acid stress.

Screening the Saccharomyces cerevisiae disruptome, profiling transcripts, and determining changes in protein expression have identified an important new role for the high-osmolarity glycerol (HOG) mitogen-activated protein kinase (MAPK) pathway in the regulation of adaptation to citric acid stress. Deletion of HOG1, SSK1, PBS2, PTC2, PTP2, and PTP3 resulted in sensitivity to citric acid. Furthermore, citric acid resulted in the dual phosphorylation, and thus activation, of Hog1p. Despite minor activation of glycerol biosynthesis, the inhibitory effect of citric acid was not due to an osmotic shock. HOG1 negatively regulated the expression of a number of proteins in response to citric acid stress, including Bmh1p. Evidence suggests that BMH1 is induced by citric acid to counteract the effect of amino acid starvation. In addition, deletion of BMH2 rendered cells sensitive to citric acid. Deletion of the transcription factor MSN4, which is known to be regulated by Bmh1p and Hog1p, had a similar effect. HOG1 was also required for citric acid-induced up-regulation of Ssa1p and Eno2p. To counteract the cation chelating activity of citric acid, the plasma membrane Ca(2+) channel, CCH1, and a functional vacuolar membrane H(+)-ATPase were found to be essential for optimal adaptation. Also, the transcriptional regulator CYC8, which mediates glucose derepression, was required for adaptation to citric acid to allow cells to metabolize excess citrate via the tricarboxylic acid (TCA) cycle. Supporting this, Mdh1p and Idh1p, both TCA cycle enzymes, were up-regulated in response to citric acid.

Adaptation, Biological↗
PubMedDate not supplied

13C-urea breath test for the diagnosis of Helicobacter pylori infection before treatment: is citric acid necessary?

AIM: 13C-urea breath test is one of the best methods for the diagnosis of Helicobacter pylori infection. Although a citric acid solution is generally used prior to urea intake, the superiority of this strategy has not been sufficiently demonstrated. Thus, our aim was to compare 13C-urea breath test with and without citric acid solution, to evaluate whether 13C-urea breath test can also achieve favourable results when the test meal is omitted. METHODS: 13C-urea breath test with and without citric acid were compared prospectively in 53 subjects without prior Helicobacter pylori eradication therapy prescription. Basal samples and at 15', 30', and 45' after taking 100 mg of 13C-urea were obtained. The gold standard for Helicobacter pylori diagnosis was the 13C-urea breath test result with citric acid at 30', and "Delta Over Baseline" values >5 at that time were considered positive. RESULTS: The prevalence of Helicobacter pylori infection was 68%. Mean Delta Over Baseline values with citric acid at 15', 30' and 45' were: 29.6+/-39, 30.8+/-37 and 24.6+/-27; whereas respective values without citric acid were lower: 14.9+/-22, 12.2+/-17 and 10D+/-13 (p<O. 001 for all comparisons, Wilcoxon test for paired data). Thus, the area under the curve (constructed with Delta Over Baseline values at different times) with citric acid was 85+/- 102, and 37+/-50 without citric acid [p<0.001). Correlation coefficient between Delta Over Baseline values with and without citric acid at 30' was 0.73 (p<0.0001). The percentage of subjects achieving the highest Delta Over Baseline value at 15', 30' and 45' with citric acid was 51%, 30% and 19%, whereas without citric acid it was 51%, 26% and 23% (non-significant differences). The area under receiver operating characteristic curve for 13C-urea breath test without citric acid was: 0.98 at 15', 1 at 30' and 0.97 at 45'. The best cut-off point for 13C-urea breath test without citric acid at 30' was anywhere between 3. 3 and 3.9 (that is, a lower value than that usually considered with citric acid), with 100% (95% confidence interval, 90-100%) sensitivity and 100% [82-100%) specificity CONCLUSIONS: 13C-urea breath test values with citric acid are higher than those obtained without citric acid, although this difference does not imply a diagnostic superiority in untreated patients when considering 13C-urea breath test without citric acid at 30'. Therefore, for the diagnosis of Helicobacter pylori infection in untreated patients, citric acid solution in 13C-urea breath test protocol can be omitted.

Adult↗
PubMed2002

High resolution SEM evaluation of dentin etched with maleic and citric acid.

OBJECTIVES: This study evaluated the ultra-morphological effects of maleic and citric acid on human dentin by means of a field emission in-lens scanning electron microscope (FEISEM). Both acids were tested on human dentin at pH 0.7 and 1.4 in aqueous solutions. METHODS: Each of 12 dentin disks were divided into four groups and exposed to either maleic acid at pH 0.7, maleic acid at pH 1.4, citric acid at pH 0.7 and citric acid at pH 1.4. All samples were then fixed and dehydrated in a critical point drying apparatus. Observations were carried out by means of a FEISEM (JEOL 890) after coating with a carbon-platinum film. RESULTS: Both acids removed smear layer and partially removed smear plugs. Details of fine structures measuring from 5 to 15 nm were shown on the intertubular demineralized dentin. Maleic acid at pH 0.7 showed the highest depth of demineralization of all the tested samples; citric acid, showed a higher depth of demineralization values when tested at pH 1.4 than at pH 0.7. SIGNIFICANCE: The FEISEM reveals ultra-structural aspects of the demineralization process of the dentin tissue of the both acids tested. Differences related to the pH of the acids were found. Images obtained at high magnification clarify the dentin collagen structure of both peritubular and intertubular dentin. Small periodic structures associated with collagen fibrils were also imagined.

Acid Etching, Dental↗
PubMed1991

Leaching with Penicillium simplicissimum: Influence of Metals and Buffers on Proton Extrusion and Citric Acid Production.

In the presence of insoluble metal oxides (industrial filter dust, zinc oxide, synthetic mixture of metal oxides), Penicillium simplicissimum developed the ability to excrete considerable amounts of citric acid (>100 mM). Parallel with the increase of citric acid concentration in the culture broth, zinc was solubilized from zinc oxide. The adsorption of filter dust onto the mycelium (the pellets formed were less than 1 mm in diameter) was required for not only the citric acid excretion but also the leaching of zinc. When the filter dust was replaced with a synthetic mixture of metal oxides or with zinc oxide in combination with trace elements, levels of adsorption and citric acid production were observed to be similar to those in experiments where industrial filter dust was used. The two most important properties of the filter dust were its heavy-metal content and its buffering capacity. These properties were simulated by adding heavy metals in soluble form (as chlorides, sulfates, or nitrates) or soluble buffers to the medium. Both heavy metals and buffers were not able to induce a citric acid efflux. As with citric acid production by Aspergillus niger, the addition of manganese lowered citric acid excretion (by 40% with metal oxide-induced citric acid efflux and by 100% with urea-induced citric acid efflux). Copper antagonized the effect of manganese. The mechanism for the bulk of citric acid excretion by P. simplicissimum, however, seemed to be different from that described for citric acid accumulation by A. niger. Because of the inefficiency of metals in solubilized form and of soluble buffers to induce a strong citric acid efflux, adsorption of an insoluble metal compound (zinc oxide) turned out to be essential. Surface phenomena possibly involving the plasma membrane H-ATPase are thought to participate in the induction of citric acid excretion by P. simplicissimum in the presence of industrial filter dust.

Journal Article↗
PubMed1993

Mathematical model for citric acid fermentation.

The kinetics for biomass proliferation, medium consumption and citric acid production in the course of citric acid fermentation were studied, and the mathematical models describing the course of citric acid fermentation were obtained in this paper. Based on the statistical data of experiment, the model was verified, and the model parameters were estimated with the results of the experiment. The results showed that the curves obtained by model calculation fitted with the ones determined by the experiments well, and the models described correctly the course of the citric acid fermentation. This is important for computer application to control the course of fermentation and realize the optimum of fermentation process.

Aspergillus niger↗
PubMed2000

Production of citric acid using immobilized conidia of Aspergillus niger.

Conidia of Aspergillus niger were immobilized in calcium alginate gel for the production of citric acid. First, the type of the preactivation medium, together with the preactivation period, was investigated. It was found that A. niger requires a 2-d preactivation period at a 0.05 g/L NH4NO3 concentration. Second, preactivated cells were used to determine the effects of nitrogen concentration and the flow rate of oxygen and air on the production of citric acid. Maximum citric acid production was attained with medium containing 0.01 g/L of NH4NO3. The rate of citric acid production in the nitrogenous medium was 33% higher when oxygen was used instead of air during the production phase. This corresponds to an increase of 85% when compared to production when neither oxygen nor air was fed into the system. In the nonnitrogenous medium citric acid concentration remained similar regardless of the use of air or oxygen. However, in the nonnitrogenous production medium, citric acid production was not influenced considerably when oxygen was used instead of air. The advantage of using immobilized cells is that production is achieved easily in the continuous system. Therefore, citric acid production was also tested using a packed-bed bioreactor, and an increase in productivity by a factor of 22 was achieved compared to the batch system.

Air↗
PubMed1981

Citric acid concentration in subclinical mastitic milk.

The effect of subclinical mastitis on the citric acid concentration of cow's milk was studied by comparing milk from the mastitic quarter with that from a healthy quarter of the same udder. Forty-two pairs of fore-milk from the morning milking of 17 cows were examined and the citric acid content was measured by an automated carboxylic acid analyzer. The citric acid concentration deceased in subclinical mastitic milk and the extent of decrease was proportional to the degree of mastitis as expressed by the quarter difference value in concentration of Na + Cl in mM/l, i.e. the increase in the Na and Cl concentrations in the abnormal milk over that found in normal milk from the same udder. The correlation coefficient between the quarter difference value of Na + Cl and the value for citric acid was -0.77, (d.f. = 46, P less than 0.001) and a linear regression equation was obtained. The result showed clearly that subclinical mastitis is one of the causes of variation in the citric acid content of cow's milk. The quantitative change in citric acid concentration in subclinical mastitic milk is discussed with reference to the admixture theory for the formation of abnormal milk.

Animals↗
PubMedDate not supplied

[Respiratory cyanide resistance in Candida lipolytica and the supersynthesis of citric acids].

The interrelationship between the cyanide resistance of respiratio and the process of citric acid synthesis was studied with various strains of Candida lipolytica. When the synthesis of citric acids was intensive, the respiration of cells was almost entirely inhibited by cyanide. The respiration became cyanide resistant only when the biosynthesis of citric acids was over. Induction of the cyanide resistance of respiration with antimycin A stopped the biosynthesis of citric acids. The cyanide resistance of respiration in yeast cultures incapable of considerable production of citric acids was displayed when the growth ceased. There was a strong direct correlation between the rate of citric acid synthesis and the degree of inhibition of the respiration by cyanide. It was concluded therefore that the process of citric acid overproduction could reset the reduction equivalents, thus making unnecessary the cyanide resistant pathway of electron transport.

Antimycin A↗
PubMedDate not supplied

The effect of citric acid on the availability of tetracyclines in calves.

The effect of citric acid on the availability of tetracyclines was studied in calves. Citric acid did not significantly increase the serum levels of tetracyclines when calves were fed low doses (6-8 mg/kg) of oxytetracycline and chlortetracycline. When the dose of chlortetracycline was increased to 50 mg/kg, addition of citric acid caused higher serum levels the first two hours after feeding. The ratio citric acid: tetracyclines was 5:1 and 25:1. The palatability of the milk replacer was reduced when large amounts of citric acid was added.

Animal Feed↗
PubMed2006

Reactivation of an aged commercial three-way catalyst by oxalic and citric acid washing.

The efficiency of dilute oxalic and citric acid solutions on improving the oxygen storage capacity (OSC) and catalytic activity of a severely aged (83,000 km) commercial three-way catalyst (TWC) has been investigated. Washing procedures applied after optimization of experimental parameters, namely, temperature, flow-rate, and concentration of acid solution, led to significant improvements of OSC and catalytic activity (based on dynamometer test measurements) of the aged TWC. The latterwas made possible due to the removal of significant amounts of various contaminants accumulated on the catalyst surface (e.g., P, S, Pb, Ca, Zn, Si, Fe, Cu, and Ni) during driving conditions, as revealed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and X-ray Photoelectron Spectroscopy (XPS) analyses. For the first time, it is demonstrated that dilute oxalic acid solution significantly improves the catalytic activity of an aged commercial TWC toward CO, Cx,Hy, and NOx conversions under real exhaust gas conditions (dynamometer tests) by two to eight times in the 250-450 degrees C range and the OSC quantity by up to 50%. Oxalic acid appears to be more efficient than citric acid in removing specifically P- and S-containing compounds from the catalyst surface, whereas citric acid in removing Pb- and Zn-containing compounds, thus uncovering surface active catalytic sites.

Catalysis↗