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At least 433 records · Page 24Linked to original sources
PubMed1996

Evaluation of citric acid and GDL in the recovery at different pH levels of Clostridium sporogenes PA 3679 spores subjected to HTST treatment conditions.

Spores of Clostridium sporogenes PA 3679 were treated at different temperatures (121, 126, 130 and 135 degrees C) in white asparagus purée (pH 5.8) and acidified with glucono-delta-lactone (GDL) and citric acid to pH levels of 5.5, 5.0 and 4.5. Afterwards, the spores were recovered in MPA3679 medium in various conditions: unacidified (pH 7.5), acidified with GDL (500 ppm) and acidified with citric acid (500 and 250 ppm) to pH levels of 6.5, 6.0 and 5.0. The results indicated that the pH levels, concentration and type of acid used act synergistically rather than independently. Citric acid has a stronger inhibiting effect than GDL on the recovery of C. sporogenes PA 3679 spores. At the higher heat treatments (130 and 135 degrees C) the major injury on the spores sensitize more than against the acids and low pH values.

Citrates↗
PubMed1986

Lack of effect of citric acid treatment of root surfaces on the formation of new connective tissue attachment.

Previous reports have described an accelerated induction of new attachment and repair of furcations in dogs after treatment of roots surfaces with citric acid, but few controlled clinical studies have examined its usefulness in surgical treatments for periodontitis. This study compared the effects of a comprehensive surgical plaque control procedure with or without citric acid treatment for generalized and localized effects on gingival height, probing pocket depth and attachment level in 72 teeth in 3 patients who were treated surgically for moderate periodontitis and examined every 3 months for 1 year. No statistically significant differences in the effects of the 2 treatments were observed. These observations suggest that there is no clinical advantage of citric acid conditioning of the root surface during surgical treatment of periodontitis.

Adult↗
PubMed2006

Immobilization of bacteria in silica matrices using citric acid in the sol-gel process.

The aim of this work was to use citric acid in the sol-gel process to generate an inorganic polymer that allows bacterial survival for long periods of time and to study the influence of different storage temperatures. We compared gram-negative Escherichia coli and gram-positive Staphylococcus aureus, immobilized and preserved at different storage temperatures in silica matrices prepared by the method proposed. Immobilized E. coli and S. aureus in silica matrices were stored in sealed tubes at 20, 4, -20, and -70 degrees C for 4 months during which the number of viable cells was analyzed. Results show that the immobilization in silica matrices using citric acid, to neutralize the alkalinity of the silica precursors, makes the technique not only biocompatible but also easier to perform since polymerization does not occur immediately as it does when hydrochloric acid is utilized.

Biotechnology↗
PubMed2000

Contribution of cyanide-insensitive respiratory pathway, catalyzed by the alternative oxidase, to citric acid production in Aspergillus niger.

In Aspergillus niger, a cyanide (CN)- and antimycin A-insensitive and salicylhydroxamic acid (SHAM)-sensitive respiratory pathway exists besides the cytochrome pathway and is catalyzed by the alternative oxidase (AOX). In this study, A. niger WU-2223L, a citric acid-producing strain, was cultivated in a medium containing 120 g/l of glucose, which is the concentration usually needed for citric acid production, and the effects of 2% (v/v) methanol, an inducer of citric acid, 2 microM antimycin A, and 1 mM SHAM on AOX activities and citric acid production were investigated. The AOX activity, measured as duroquinol oxidase, was localized in the purified mitochondria regardless of the presence of any additives. When WU-2223L was cultivated with antimycin A or methanol, both citric acid production and citric acid productivity, shown as the ratio of production per mycelial dry weight, increased with the increase of both the activity of AOX and the rate of CN-insensitive and SHAM-sensitive respiration. On the other hand, when WU-2223L was cultivated with SHAM, an inhibitor of AOX, the CN-insensitive and SHAM-sensitive respiration was not detected and the citric acid production and the productivity drastically decreased, although mycelial growth was not affected. These results clearly indicated that the CN-insensitive and SHAM-sensitive respiration catalyzed by AOX, localized in the mitochondria, contributed to citric acid production by A. niger.

Aspergillus niger↗
PubMed1990

Effect of methionine sulfoximine on pyruvate dehydrogenase, citric acid cycle enzymes and aminotransferases in the subcellular fractions isolated from rat cerebral cortex.

The effect of acute and subacute doses of L-methionine-DL-sulfoximine (MSI) were studied on the activities of pyruvate dehydrogenase, enzymes of citric acid cycle and aspartate and alanine aminotransferases in the mitochondria, synaptosomes and cytosol of rat brain. In general, the activities of pyruvate dehydrogenase and of the citric acid cycle enzymes, except malate dehydrogenase (malate----oxaloacetate), were elevated in all 3 subcellular fractions. Malate dehydrogenase activity (malate----oxaloacetate) was suppressed in the mitochondria while the activity of this enzyme in the reverse direction was enhanced in the cytosol. Activities of aspartate and alanine aminotransferases were suppressed under these conditions. As the effects of MSI on these enzymes were similar to those observed upon the administration of ammonium salts, it is suggested that the hyperammonemic state induced by MSI might derange the operation of the malate-aspartate shuttle. Increased activities of citric acid cycle enzymes in the cytosol suggested the existence of a small population of mitochondria which was highly vulnerable either to ammonia or to MSI.

Ammonia↗
PubMed1982

Trace metal-citric acid complexes as inhibitors of calcification and crystal growth. I. Effects of Fe(III), Cr(III) and Al(III) complexes on calcium phosphate crystal growth.

The crystal growth of calcium phosphate has been shown to be inhibited by a low molecular weight Fe(III)-citric acid complex formed when there are high ratios of citrate:iron at neutral pH in aqueous solution. Synergism with citric acid was also observed in systems containing Al(III) or Cr(III) ion, but different unknown complexes seemed to be involved. These results are in qualitative agreement with a preceding study involving calcification of an organic matrix. Since chelating agents like citric acid can compete with the storage proteins for iron, we suggest that the Fe(III)-citrate complexes studied here may be formed in vivo and participate in regulating biologic calcification.

Aluminum↗
PubMed2004

Microorganisms growth in endodontic citric-acid solutions with and without microbiological stabilizer.

The purpose of this study was to determine if citric-acid solutions for endodontic use can become contaminated and if the addition of a microbiological stabilizer to the acid would modify this situation. Five types of microorganisms were inoculated in tubes containing 10% citric-acid solutions, pH 1.8 (group A1), and 10% solution, pH 1.8, combined with 0.1% sodium benzoate (group A2). The results demonstrated that solutions of group A1 were contaminated with Candida albicans in 100% of the tubes, Escherichia coli in 80%, and Enterococcus faecalis in 50%. When stabilizer was added (group A2), C. albicans grew in only 30% of tubes and all bacterial species were neutralized.

Anti-Infective Agents↗
PubMed1983

Pharmacokinetics of chlortetracycline potentiation with citric acid in the chicken.

Serum concentrations of chlortetracycline (CTC) in healthy chickens were determined for the 24-hour period after they were given CTC (with and without citric acid) as an oral (25 mg/kg) or IV (0.9 mg/kg) dose. The oral time-course drug data were fitted adequately by a 2-compartment pharmacokinetic model with absorption. The resulting absorption rate constant (Ka) for the birds orally given CTC with citric acid was nearly equal to that for the birds given CTC alone. Although the uptake of orally administered CTC was rapid, only a small fraction of the dose was absorbed. The administration of citric acid-CTC significantly increased the mean serum concentration of CTC and the fraction of the dose absorbed. The citric acid-CTC mixture also produced significantly higher elimination (Kel) and distribution (K12) rate constants for CTC.

Administration, Oral↗
PubMed1997

Uptake and export of citric acid by Aspergillus niger is reciprocally regulated by manganese ions.

The uptake as well as the export of citric acid by Aspergillus niger occur by active, deltapH-driven, H(+)-symport dependent systems. They are inhibited by nonmetabolizable tricarboxylic acid analogues and phthalic acid, and by several other mono-, di- and tribasic organic acids. However, citrate export could only be demonstrated in a mycelium cultivated under manganese-deficient growth conditions, whereas the uptake of citrate from the medium was only detectable upon precultivation of A. niger in a medium supplemented with Mn2+ ions. In addition, the uptake of citrate was dependent on the presence of Mn2+ ions in the assay, and inhibited by EDTA. This requirement for Mn2+ could also be partially fulfilled by Mg2+, Fe2+ or Zn2+, whereas Cu2+ ions inhibited citrate transport. The observed divergent effects of manganese ions on citrate uptake and citrate export may be a major reason for the well documented requirement for manganese deficiency of citric acid accumulation.

Aspergillus niger↗
PubMedDate not supplied

Seminal fructose, citric acid and phosphatase levels and their relation to the sperm count in man.

Seminal fructose, citric acid and phosphatase levels were estimated in 60 normal adults and compared with 60 oligospermic and 24 azoospermic Indian subjects. In normal group, the seminal plasma fructose level and acid phosphatase activity showed a fall as the sperm count increased. As compared to normals, significantly higher mean values for fructose and acid phosphatase activity were observed in oligospermic and azoospermic groups. Seminal alkaline phosphatase activity did not show any relationship with sperm count. Similarity in changes observed in seminal fructose and acid phosphatase levels with respect to seminal citric acid content and sperm concentration suggests that both these parameters are probably regulated by similar physiological mechanism.

Acid Phosphatase↗
PubMed1994

Non-steady state model applicable to NMR studies for calculating flux rates in glycolysis, gluconeogenesis, and citric acid cycle.

We present a mathematical model for calculating most reaction rates of glycolysis, gluconeogenesis and citric acid cycle in mammalian cells. The model also includes cycles such as the "phosphoenolpyruvate (PEP)-->pyruvate-->oxaloacetate-->PEP" cycle and the "pyruvate-->acetyl-CoA-->citrate-->citric acid cycle-->oxaloacetate-->PEP--> pyruvate" cycle. The model, which does not require steady state conditions, is based on a set of equations, each one describing the fates of a given carbon of a selected intermediate. These fates are expressed as ratios of integrated transfer of this carbon to corresponding carbons in subsequent metabolites. At each bifurcation, the sum of all proportions adds up to 1. Among several calculation routes to determine a proportion value, we chose the one that was based on the most reliable parameter determined experimentally. The data introduced in the model are the micrograms of atom of traced carbon measured on each carbon of a number of products (corrected for natural tracer abundance). These incorporations can be measured by 13C NMR, gas chromatography-mass spectroscopy, or 14C counting. Thanks to its flexibility, this model can be applied to data obtained with substrates other than glucose under many experimental conditions.

Animals↗
PubMed1982

Effect of root surface alterations on periodontal healing. II. Citric acid treatment of the denuded root.

A companion study reported that new connective tissue attachment did not occur to a surgically denuded root surface when transplanted into a normal periodontium. It was the purpose of this study to evaluate periodontal healing adjacent to a citric acid treated denuded root surface. In four squirrel monkeys, 12 teeth were extracted and reimplanted after surgical denudation and citric acid conditioning of the coronal root surface. The study design provided three teeth for histologic analysis at 1, 3, 7 and 21 days after reimplantation. One and 3 days after reimplantation a zone of fibrin containing inflammatory cells and erythrocytes was interposed between the root surface and remaining periodontal fibers. The fibrin network appeared to be attached to the root surface by arcade-like formations. The apical termination of the epithelium was located at the coronal extent of the fibrin zone. Granulation tissue and new fibers were aggregating along and perpendicular to the root surface at 7 days, and new connective tissue attachment had been established at 21 days. Extensive root resorption was present along the intra-alveolar part of the root surface. Epithelium had not migrated apically along the denuded root surfaces. The results indicated that citric acid treatment of denuded root surfaces resulted in new connective tissue attachment, and the response appeared to be dependent upon early establishment of fibrin linkage with the root surface.

Animals↗
PubMed1979

Effect of growth condition on enzymes of the citric acid cycle and the glyoxylate cycle in the photosynthetic bacterium Rhodopseudomonas palustris.

The enzymes of the citric acid and glyoxylate cycles as well as RuBP4 carboxylase were measured in cell-free extracts from Rhodopseudomonas palustris after growth under chemoheterotrophic, photoheterotrophic and photolithotrophic conditions. Although the citric acid cycle was found to be complete under all growth conditions, significant differences in certain enzyme activities occurred as a function of the different energy sources applied. The glyoxylate cycle also was complete under all growth conditions with highest isocitrate lyase activity seen after photoheterotrophic growth on acetate. Photo- and chemoheterotrophic growth on malate reduced the isocitrate lyase. The activity was not repressed further by photolithotrophic growth on thiosulfate. RuBP carboxylase activity, present under photolithotrophic conditions, was repressed by chemoheterotrophic growth but was not decreased by the presence of organic substrates during photoheterotrophic growth.

Aerobiosis↗
PubMed1981

[Effect of oxygen partial pressure on citric acid synthesis in Saccharomycopsis lipolytica using n-alkanes].

The dependence of growth formation of citric acids (citrate: isocitrate = 1:1) on oxygen parital pressure of an alkane utilising yeast Saccharomycopsis lipolytica was investigated. During growth oxygen corresponds to a Michaelis-Menten-kinetics (Ks = 2.0 . 10(-5) M). The respiration quotient RQ for a dissolved oxygen concentration in the range of 10-100% (air saturation) is 0.46 +/- +/- 0.04. The phase of product formation is characterized by 3 sections. Immediately after N-exhaustion the cell activities are the highest. They decline during the first 30 hours of production. Besides the production of reserve material in this first section the highest production rate for citrate and isocitrate is observed. The rate of citric acid production depends on the oxygen partial pressure and is governed by Michaelis-Menten-kinetics. The specific production rate and the rate of oxygen consumption correspond to KS-values of 4.0 X 10(-5) and 3.3 X 10(-5) M, respectively. The RQ-value declines to a constant value of 0.23 +/- 0.02 and is not influenced by oxygen partial pressures in the range of 10--100% (related to air saturation). During the second section cell activities remain nearly constant for about 100 h. Due to this constancy the following equation could be derived: 14 O2 + C15H32 leads to 2 C6H8O7 + 3 CO2 + 8 H2O. In the third section the cell activities decline again.

Aerobiosis↗
PubMed2005

Citric acid prolongs the gastro-retention of a floating dosage form and increases bioavailability of riboflavin in the fasted state.

A floating dosage form based on calcium alginate beads has been developed. Riboflavin, was selected as the model drug and successfully incorporated into calcium alginate beads. The aims of the current study were to: (a) assess the influence of prolonged gastro-retention on the bioavailability of riboflavin from freeze dried calcium alginate beads administered under varying conditions of food intake and (b) to investigate the potential of citric acid to delay the gastric emptying of the calcium alginate beads. Gamma scintigraphy was selected as the method to monitor the movement of the calcium alginate beads in vivo. Riboflavin concentrations in the urine were analysed by HPLC. Prolonged gastro-retention can be achieved, in the fasted state, when citric acid solution is used as an administering vehicle. However, prolonged gastro-retention is not achieved to the same extent when the gastric emptying times are compared to those obtained in the fed state. The bioavailability of riboflavin improved when calcium alginate beads were administered in the fasted state with citric acid solution, compared to the bioavailability obtained when the calcium alginate beads were administered in the absence of citric acid.

Adult↗
PubMedDate not supplied

[Effect of products of thermophilic methane fermentation on the conidial activation and citric acid biosynthesis by the fungus Aspergillus niger].

The effect of products of thermophilic methane fermentation (PTMF) and their hydrolyzates on the conidial germination and citric acid bioysnthesis by the fungus Aspergillus niger when cultivated on the synthetic and molasses media was investigated. An addition of the above products increased the amount of germinated conidia on the synthetic medium by 1.2--2 times and on the molasses medium by 1.1--1.4 times. The citric acid yeild per unit surface area on the two media grew by 60--100% and 10--20%, respectively. Optimal concentration of dry preparations of PTMF was 5--7.5 mg/100 ml and that of their hydrolyzates was 0.5--1.5 ml/100 ml of the medium. An addition of PTMF to the molasses medium resulted both in an increased yeild of citric acid (1500--1700 g/m2/day) and in reduced (by 12--24 hours) time of the biosynthesis process.

Aspergillus niger↗
PubMed1995

Sudden substrate dilution induces a higher rate of citric acid production by Aspergillus niger.

On the basis of the present knowledge of Aspergillus niger metabolism during citric acid fermentation, an idea on how to improve the process was formed. Initially, a higher sucrose concentration was used for the germination of spores, which caused a higher intracellular level of the osmoregulator, glycerol, to be present. When citric acid started to be excreted into the medium, the substrate was suddenly diluted. Optimization of this procedure resulted in a nearly tripled volumetric rate (grams per liter per hour) of acid production, while the overall fermentation time was halved compared with the usual batch process. Yet, a characteristic delay was observed at the start of the acid excretion after the dilution. Hypo-osmotic shock caused a prominent elevation of intracellular cyclic AMP levels. Simultaneously, the specific activity of 6-phosphofructo-1-kinase increased significantly, probably due to phosphorylation of the protein molecule by cyclic AMP-dependent protein kinase. Specific 6-phosphofructo-1-kinase activity was much higher in the treated than in the normally growing mycelium. The metabolic flow through glycolysis was expected to be higher, which should contribute to a higher volumetric rate of acid production.

Aspergillus niger↗