Showing papers on "Citric acid published in 2004"

Citric acid cycle intermediates as ligands for orphan G-protein-coupled receptors

Abstract: The citric acid cycle is central to the regulation of energy homeostasis and cell metabolism. Mutations in enzymes that catalyse steps in the citric acid cycle result in human diseases with various clinical presentations. The intermediates of the citric acid cycle are present at micromolar concentration in blood and are regulated by respiration, metabolism and renal reabsorption/extrusion. Here we show that GPR91 (ref. 3), a previously orphan G-protein-coupled receptor (GPCR), functions as a receptor for the citric acid cycle intermediate succinate. We also report that GPR99 (ref. 4), a close relative of GPR91, responds to alpha-ketoglutarate, another intermediate in the citric acid cycle. Thus by acting as ligands for GPCRs, succinate and alpha-ketoglutarate are found to have unexpected signalling functions beyond their traditional roles. Furthermore, we show that succinate increases blood pressure in animals. The succinate-induced hypertensive effect involves the renin-angiotensin system and is abolished in GPR91-deficient mice. Our results indicate a possible role for GPR91 in renovascular hypertension, a disease closely linked to atherosclerosis, diabetes and renal failure.

Novel Citric Acid‐Based Biodegradable Elastomers for Tissue Engineering

Abstract: Tissue engineering often requires the use of a three dimensional scaffold for cells to grow on and differentiate properly. Generally, the ideal scaffold should be biocompatible, biodegradable, allow for proper cell loading, be cell-responsive and regulate the cell multiplication and differentiation, and possess mechanical and physical properties that are suitable for the target application. As many tissues in the body have elastomeric properties, successful tissue engineering of these requires the development of compliant biodegradable scaffolds. Despite the recognized importance of mechanical stimuli on tissue development, there has been a dearth of research into the design and evaluation of elastomeric biodegradable scaffolds. The few materials that have been reported in the literature require complex and costly synthesis procedures, which translate into higher manufacturing costs and hinder the commercial and clinical implementation of tissue engineering. Herein we describe the synthesis and characterization of a novel biodegradable elastomer, poly(1,8-octanediol-co-citric acid) (POC), that has potential for use in tissue engineering, in particular the engineering of small-diameter blood vessels. Development of materials for this application is important as cardiovascular disease affecting blood vessels is the principal cause of death in the U.S.A. POC has the following advantages: non-toxic monomers, relatively simple synthesis that can be carried out under mild conditions without addition of toxic catalysts or crosslinking reagents (making it a good candidate for drug delivery and cost-effective scale-up), controllable mechanical and biodegradation properties, easy processing, and inherent surface affinity for various cell types.

Gastroretentive drug delivery system of ranitidine hydrochloride: Formulation and in vitro evaluation

Abstract: The purpose of this research was to prepare a gastroretentive drug delivery system of ranitidine hydrochloride. Guar gum, xanthan gum, and hydroxypropyl methylcellulose were evaluated for gel-forming properties. Sodium bicarbonate was incorporated as a gas-generating agent. The effects of citric acid and stearic acid on drug release profile and floating properties were investigated. The addition of stearic acid reduces the drug dissolution due to its hydrophobic nature. A 32 full factorial design was applied to systemically optimize the drug release profile. The amounts of citric acid anhydrous (X1) and stearic acid (X2) were selected as independent variables. The times required for 50% (t50) and 80% drug dissolution (t80), and the similarity factor f2 were selected as dependent variables. The results of the full factorial design indicated that a low amount of citric acid and a high amount of stearic acid favors sustained release of ranitidine hydrochloride from a gastroretentive formulation. A theoretical dissolution profile was generated using pharmacokinetic parameters of ranitidine hydrochloride. The similarity factor f2 was applied between the factorial design batches and the theoretical dissolution profile. No significant difference was observed between the desired release profile and batches F2, F3, F6, and F9. Batch F9 showed the highest f2 (f2=75) among all the batches, and this similarity is also reflected in t50 (∼214 minutes) and t80 (∼537 minutes) values. These studies indicate that the proper balance between a release rate enhancer and a release rate retardant can produce a drug dissolution profile similar to a theoretical dissolution profile.

Nitrate Reduction by Zerovalent Iron: Effects of Formate, Oxalate, Citrate, Chloride, Sulfate, Borate, and Phosphate

Abstract: Recent studies have shown that zerovalent iron (Fe0) may potentially be used as a chemical medium in permeable reactive barriers (PRBs) for groundwater nitrate remediation; however, the effects of commonly found organic and inorganic ligands in soil and sediments on nitrate reduction by Fe0 have not been well understood. A 25.0 mL nitrate solution of 20.0 mg of N L-1 (1.43 mM nitrate) was reacted with 1.00 g of Peerless Fe0 at 200 rpm on a rotational shaker at 23 °C for up to 120 h in the presence of each of the organic acids (3.0 mM formic, 1.5 mM oxalic, and 1.0 mM citric acids) and inorganic acids (3.0 mM HCl, 1.5 mM H2SO4, 3.0 mM H3BO3, and 1.5 mM H3PO4). These acids provided an initial dissociable H+ concentration of 3.0 mM available for nitrate reduction reactions under conditions of final pH < 9.3. Nitrate reduction rates (pseudo-first-order) increased in the order: H3PO4 < citric acid < H3BO3 < oxalic acid < H2SO4 < formic acid < HCl, ranging from 0.00278 to 0.0913 h-1, corresponding to surface a...

Development and Physicochemical Characterization of New Resistant Citrate Starch from Different Corn Starches

Abstract: Resistant starch has drawn broad interest for both potential health benefits and functional properties. In this study, a technology was developed to increase resistant starch content of corn starch using esterification with citric acid at elevated temperature. Waxy corn, normal corn and high-amylose corn starches were used as model starches. Citric acid (40% of starch dry weight) was reacted with corn starch at different temperatures (120–150°C) for different reaction times (3–9 h). The effect of reaction conditions on resistant starch content in the citrate corn starch was investigated. When conducting the reaction at 140°C for 7 h, the highest resistant starch content was found in waxy corn citrate starch (87.5%) with the highest degree of substitution (DS, 0.16) of all starches. High-amylose corn starch had 86.4% resistant starch content and 0.14 DS, and normal corn starch had 78.8% resistant starch and 0.12 DS. The physicochemical properties of these citrate starches were characterized using various analytical techniques. In the presence of excess water upon heating, citrate starch made from waxy corn starch had no peak in the DSC thermogram, and small peaks were found for normal corn starch (0.4 J/g) and Hylon VII starch (3.0 J/g) in the thermograms. This indicates that citrate substitution changes granule properties. There are no retrogradation peaks in the thermograms when starch was reheated after 2 weeks storage at 5°C. All the citrate starches showed no peaks in RVA pasting curves, indicating citrate substitution changes the pasting properties of corn starch as well. Moreover, citrate starch from waxy corn is more thermally stable than the other citrate starches.

Relationship Between Host Acidification and Virulence of Penicillium spp. on Apple and Citrus Fruit.

Abstract: Penicillium expansum, P. digitatum, and P. italicum acidify the ambient environments of apple and citrus fruit during decay development. They use two mechanisms for this: the production of organic acids, mainly citric and gluconic, and NH4+ utilization associated with H+ efflux. Exposure of P. expansum and P. digitatum hyphae to pH 5.0 increased their citric acid production, compared with the production of organic acids at acidic ambient pH. In decayed fruit, both pathogens produced significant amounts of citric and gluconic acids in the decayed tissue and reduced the host pH by 0.5 to 1.0 units. Ammonium depletion from the growth medium or from the fruit tissue was directly related to ambient pH reduction. Analysis of transcripts encoding the endopolygalacturonase gene, pepg1, from P. expansum accumulated under acidic culture conditions from pH 3.5 to 5.0, suggesting that the acidification process is a pathogenicity enhancing factor of Penicillium spp. This hypothesis was supported by the findin...

Enhanced phytoextraction: in search of EDTA alternatives.

Abstract: Enhanced phytoextraction proposes the use of soil amendments to increase the heavy-metal content of above-ground harvestable plant tissues. This study compares the effect of synthetic aminopolycarboxylic acids [ethylenediamine tetraacetatic acid (EDTA), nitriloacetic acid (NTA), and diethylenetriamine pentaacetic acid (DTPA)] with a number of biodegradable, low-molecular weight, organic acids (citric acid, ascorbic acid, oxalic acid, salicylic acid, and NH4 acetate) as potential soil amendments for enhancing phytoextraction of heavy metals (Cu, Zn, Cd, Pb, and Ni) by Zea mays. The treatments in this study were applied at a dose of 2 mmol/kg(-1) 1 d before sowing. To compare possible effects between presow and postgermination treatments, a second smaller experiment was conducted in which EDTA, citric acid, and NH4 acetate were added 10 d after germination as opposed to 1 d before sowing. The soil used in this screening was a moderately contaminated topsoil derived from a dredged sediment disposal site. This site has been in an oxidized state for more than 8 years before being used in this research. The high carbonate, high organic matter, and high clay content characteristic to this type of sediment are thought to suppress heavy-metal phytoavailability. Both EDTA and DTPA resulted in increased levels of heavy metals in the above-ground biomass. However, the observed increases in uptake were not as large as reported in the literature. Neither the NTA nor organic acid treatments had any significant effect on uptake when applied prior to sowing. This was attributed to the rapid mineralization of these substances and the relatively low doses applied. The generally low extraction observed in this experiment restricts the use of phytoextraction as an effective remediation alternative under the current conditions, with regard to amendments used, applied dose (2 mmol/kg(-1) soil), application time (presow), plant species (Zea mays), and sediment (calcareous clayey soil) under study.

Changes in physicochemical characteristics and volatile constituents of strawberry (Cv. Cigaline) during maturation.

Abstract: Changes in the volatile composition of strawberries (cv. Cigaline) at six stages of maturity, from 28 to 44 days after anthesis, were investigated over two harvesting seasons. Volatiles were isolated by direct solvent extraction and analyzed by means of GC-FID and GC-MS, with special attention to the quantification of furanones. Firmness, skin color, soluble solids (SS), titratable acidity (TA), SS/TA ratio, organic acids, and sugars were also determined. With increasing maturity, soluble solids, SS/TA ratio, Minolta a value, and levels of sucrose, glucose, fructose, and malic acid increased, whereas Minolta L value, hue angle (), titratable acidity, and levels of citric acid decreased. Furanones and esters were generally not detected before half-red fruits, whereas C(6) compounds were the main compounds in immature fruits. During maturation, levels of these so-called green components decreased drastically, whereas levels of key flavor compounds increased significantly and were closely correlated with skin color development. Maximum volatile production was observed in fully red fruits.

Structure and Characterization of Flavolipids, a Novel Class of Biosurfactants Produced by Flavobacterium sp. Strain MTN11

Abstract: Herein we report the structure and selected properties of a new class of biosurfactants that we have named the flavolipids. The flavolipids exhibit a unique polar moiety that features citric acid and two cadaverine molecules. Flavolipids were produced by a soil isolate, Flavobacterium sp. strain MTN11 (accession number AY162137), during growth in mineral salts medium, with 2% glucose as the sole carbon and energy source. MTN11 produced a mixture of at least 37 flavolipids ranging from 584 to 686 in molecular weight (MW). The structure of the major component (23%; MW = 668) was determined to be 4-[[5-(7-methyl-(E)-2-octenoylhydroxyamino)pentyl]amino]-2-[2-[[5-(7-methyl-(E)-2-octenoylhydroxyamino)pentyl]amino]-2-oxoethyl]-2-hydroxy-4-oxobutanoic acid. The partially purified flavolipid mixture isolated from strain MTN11 exhibited a critical micelle concentration of 300 mg/liter and reduced surface tension to 26.0 mN/m, indicating strong surfactant activity. The flavolipid mixture was a strong and stable emulsifier even at concentrations as low as 19 mg/liter. It was also an effective solubilizing agent, and in a biodegradation study, it enhanced hexadecane mineralization by two isolates, MTN11 (100-fold) and Pseudomonas aeruginosa ATCC 9027 (2.5-fold), over an 8-day period. The flavolipid-cadmium stability constant was measured to be 3.61, which is comparable to that for organic ligands such as oxalic acid and acetic acid. In summary, the flavolipids represent a new class of biosurfactants that have potential for use in a variety of biotechnological and industrial applications.

Evidence of a New Role for the High-Osmolarity Glycerol Mitogen-Activated Protein Kinase Pathway in Yeast: Regulating Adaptation to Citric Acid Stress

Abstract: 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 Ca2+ 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.

Microbial recovery of copper from printed circuit boards of waste computer by Acidithiobacillus ferrooxidans.

Abstract: The bioleaching of copper contained in the printed circuit boards (PCB) of waste computers by A. ferrooxidans was studied. The Fe oxidation rates by A. ferrooxidans in the 9K medium supplemented with the leachate of PCB (0.15-0.13 g L(-1) d(-1)) were similar to that in the 9K medium without the leachate (0.15 g L(-1) d(-1)). This finding suggests that the leachate of PCB did not seriously affect the bioleaching process by this bacterium. The amount of copper leached from PCB shreds increased with the addition of ferrous ion and reached up to 5190 mg L(-1) when the initial concentration of Fe2+ ion was 7 g L(-1). As the microbial leaching progressed, pale brown precipitate was observed to form in the solution. Based on the total amount of copper, both in solution and precipitate, the optimal addition of ferrous ion for the leaching of copper was around 7 g L(-1). When citric acid was not added, only about 37 wt% of the total leached copper remained dissolved; however, the amount of dissolved copper increased to greater than 80 wt% in the presence of citric acid. This fact indicates that the addition of a complexing agent (citric acid) to the bioleaching solution can raise the solubility of the leached metal ions.

Sorption of copper and lead by citric acid modified wood

Abstract: The sorption characteristics of citric acid modified wood to remove copper and lead ions from aqueous solution under batch conditions have been investigated Sorption was pH dependent with increasing uptake at higher pH values The kinetics of sorption for both ions was rapid with 90% sorption taking place within the first 60 min regardless of its initial concentration Sorption can be explained by a second-order kinetics model from which the rate constant, the equilibrium sorption capacity and the initial rate were calculated From these parameters, the predictive models for Cu and Pb sorbed (q t) in time t and at an initial concentration (C o) are given by q t=C o t[031C o−229+(004C o+519)t] and q t=C o t/[006C o−659+(001C o+448)t] for Cu and Pb, respectively Using these models the predicted and experimental uptakes of Cu and Pb were compared and discussed Maximum sorption capacities of modified wood under present experimental conditions were 2370 and 8264 mg/g for Cu and Pb, respectively However, for untreated wood the corresponding values were 256 and 771 mg/g indicating a tenfold increase in sorption upon citric acid modification Ethylene diamine tetraacetic acid and nitrilotriacetic acid complexed with both ions render sorption less favorably However, salicylic acid had little influence In a binary system, Pb ions were more favorably sorbed than Cu ions which could be due to the larger ionic radius of the former ions

Hard surface cleaning compositions

Abstract: Improved hard surface cleaning compositions having an acidic pH provide good removal of soap scum stains. Compositions of the present invention comprise an acidic constituent which comprises either citric acid alone or citric acid in combination with an acid selected from the group consisting of sorbic acid, acetic acid, boric acid, formic acid, maleic acid, adipic acid, lactic acid, malic acid, malonic acid, glycolic acid, and mixtures thereof; at least one anionic surfactant; at least one thickener; at least one scrubbing agent; one or more optional constituents; and the balance water; wherein the aqueous hard surface cleaning composition exhibits a pH of 6.0 or less.

Adhesive properties of modified soybean flour in wheat straw particleboard

Abstract: The objective of this research was to improve mechanical properties and water resistance of wheat straw–soy flour particleboard by chemically modifying soy flour. Urea and urease inhibitor N -( n -butyl) thiophosphoric triamide ( n BTPT) were used to modify the proteins. Boric acid and citric acid along sodium hypophosphite monohydrate were used to modify soy carbohydrates. Sodium hydroxide was used to unfold protein molecules. The combined effect of the chemicals was also studied. Particleboard bonded by urea and high concentrations of n BTPT treated soy flour improved mechanical properties, that bonded by boric acid treated soy flour had better water resistance. The adhesive made from soy flour treated with 1.5 M urea, 0.4% n BTPT, 7% citric acid, 4% NaH 2 PO 2 , 3% boric acid, and 1.85% NaOH, produced particleboard with the maximum mechanical strength and water resistance.

Effectiveness of Onboard Application of 4-Hexylresorcinol in Inhibiting Melanosis in Shrimp (Parapenaeus longirostris)

Abstract: Inhibition of melanosis in shrimp (Parapenaeus longirostris) captured at different times of year and treated with different 4-hexylresorcinol-based formulations onboard ship was studied. Melanosis inhibition increased with inhibitor concentration. The 4-hexylresorcinol proved effective at extending shelf life over that of untreated shrimp at all the concentrations tested. Combining the inhibitor with citric acid, ascorbic acid, and acetic acid did not increase the extent of melanosis inhibition but did noticeably improve shrimp appearance. Adding ethylenediaminetetraacetic acid (EDTA) and sodium pyrophosphate to the formulation enhanced melanosis inhibition at all times of year. Spray application of the inhibitor formulation extended shelf life compared with dipping and dusting, but dusting resulted in the lowest melanosis levels for a given formulation composition and concentration.

Decalcification of root canal dentine by citric acid, EDTA and sodium citrate

Abstract: Aim To measure the demineralization capability of 1 and 10% citric acid, 10% sodium citrate and 17% EDTA during immersions of 5, 10 and 15 min on root canal dentine. Methodology Crowns were sectioned from eight maxillary canines. The cementum was removed from the cervical third of the roots to expose the dentine. Canals were prepared using a handpiece-mounted Largo Peeso reamer. A 3-mm thick cross-sectional slice was obtained from the cervical third of each root. Each slice was sectioned into four equal parts. These specimens were assigned to one of four groups (n = 8) for the application of 1% citric acid, 10% citric acid, 10% sodium citrate or 17% EDTA. Each specimen underwent three successive 5-min immersions in each solution at room temperature. The solutions were not renewed between immersions. Two millimetres of solution were collected from the extracts and lanthanum oxide was added for the calcium reading by spectrophotometry. To compare the amounts of calcium removed by each solution, the Friedman test was used for the global comparison and the Wilcoxon test for paired comparisons. Differences between groups were evaluated using the Kruskal–Wallis test for the global comparison and Mann–Whitney test for paired comparisons. Results Overall, 1 and 10% citric acid were more effective than EDTA or sodium citrate at the three immersion times (P < 0.001); 10% citric acid was more effective than 1% citric acid (P < 0.001). EDTA and 1 and 10% citric acid showed decreasing effectiveness with time, and the decrease was significant for citric acid at both concentrations (P < 0.001). Although sodium citrate removed little calcium during the three time periods, the small increase recorded was significant (P < 0.01). Conclusions Citric acid at 10% was the most effective decalcifying agent, followed by 1% citric acid, 17% EDTA and 10% sodium citrate.

Extraction and Characterization of Pectin from Apple (Malus Pumila. Cv Amri) Peel Waste

Abstract: Apple peel, the major waste in preserves manufacturing, contained 1.21% pectin. Peel waste could be stabilized with 600 ppm sulphur dioxide and 1% citric acid. Pectin extraction was better in citric acid than hydrochloric acid. The pectin powder was prepared by triple extraction with citric acid solution (1%) clarification through sedimentation, concentration (24°B), precipitation using ethyl alcohol, vacuum drying and grinding. Physico-chemical properties of pectin powder revealed moisture (10.0%), total ash (1.4%), equivalent weight (652.48), methoxyl content (3.7%), anhydrouronic acid (62.82%), degree of esterification (33.44%), acetyl value (0.68), and jelly grade (80).

Pyruvate and citric acid cycle carbon requirements in isolated skeletal muscle mitochondria.

Abstract: Carbohydrate depletion precipitates fatigue in skeletal muscle, but, because pyruvate provides both acetyl-CoA for mainline oxidation and anaplerotic carbon to the citric acid cycle (CAC), the mech...