Showing papers on "Citric acid published in 2001"

The hygroscopic properties of dicarboxylic and multifunctional acids: measurements and UNIFAC predictions.

Abstract: The role of water-soluble organic compounds on the hygroscopic properties of atmospheric aerosols has recently been the subject of many studies. In particular, low molecular weight dicarboxylic acids and some multifunctional organic acids have been found or are expected to exist in atmospheric aerosols in urban, semiurban, rural, and remote sites. Unlike for their inorganic counterparts, the hygroscopic properties of organic acids have not been well characterized. In this study, the hygroscopic properties of selected water-soluble dicarboxylic acids (oxalic acid, malonic acid, succinic acid, and glutaric acid) and multifunctional acids (citric acid, DL-malic acid, and L-(+)-tartaric acid) were studied using single droplets levitated in an electrodynamic balance at 25 degrees C. The water activities of bulk samples of dilute solutions were also measured. Solute evaporation was observed in the dicarboxylic acids but not in the multifunctional acids. Oxalic acid, succinic acid, and glutaric acid droplets crystallize upon evaporation of water, but, except for glutaric acid droplets, do not deliquesce even at 90% relative humidity (RH). Mass transfer limitation of the deliquescence process was observed in glutaric acid. Neither crystallization nor deliquescence was observed in malonic acid, citric acid, DL-malic acid, or L-(+)-tartaric acid. Malonic acid and these three hydroxy-carboxylic acids absorb water even at RH much lower than their respective deliquescence RH. The growth factor (Gf), defined as the ratio of the particle diameter at RH = 10% to that at RH = 90%, of oxalic acid and succinic acid was close to unity, indicating no hygroscopicity in this range. The remaining acids (malonic acid, glutaric acid, citric acid, malic acid, and tartaric acid) showed roughly similar hygroscopicity of a Gf of 1.30-1.53, which is similar to that of "more hygroscopic" aerosols in field measurements reported in the literature. A generalized equation for these four acids, Gf = (1-aw)-0.163, was developed to represent the hygroscopicity of these acids. Water activity predictions from calculations using the UNIFAC model were found to agree with the measured water activity data to within 40% for most of the acids but the deviations were as large as about 100% for malic acid and tartaric acid. We modified the functional group interaction parameters of the COOH(-H20, OH-H20, and OH-COOH pairs by fitting the UNIFAC model with the measured data. The modified UNIFAC model improves the agreement of predictions and measurements to within 38% for all the acids studied.

Overexpression of Malate Dehydrogenase in Transgenic Alfalfa Enhances Organic Acid Synthesis and Confers Tolerance to Aluminum

Abstract: Al toxicity is a severe impediment to production of many crops in acid soil. Toxicity can be reduced through lime application to raise soil pH, however this amendment does not remedy subsoil acidity, and liming may not always be practical or cost-effective. Addition of organic acids to plant nutrient solutions alleviates phytotoxic Al effects, presumably by chelating Al and rendering it less toxic. In an effort to increase organic acid secretion and thereby enhance Al tolerance in alfalfa (Medicago sativa), we produced transgenic plants using nodule-enhanced forms of malate dehydrogenase and phosphoenolpyruvate carboxylase cDNAs under the control of the constitutive cauliflower mosaic virus 35S promoter. We report that a 1.6-fold increase in malate dehydrogenase enzyme specific activity in root tips of selected transgenic alfalfa led to a 4.2-fold increase in root concentration as well as a 7.1-fold increase in root exudation of citrate, oxalate, malate, succinate, and acetate compared with untransformed control alfalfa plants. Overexpression of phosphoenolpyruvate carboxylase enzyme specific activity in transgenic alfalfa did not result in increased root exudation of organic acids. The degree of Al tolerance by transformed plants in hydroponic solutions and in naturally acid soil corresponded with their patterns of organic acid exudation and supports the concept that enhancing organic acid synthesis in plants may be an effective strategy to cope with soil acidity and Al toxicity.

Adhesion to and Decalcification of Hydroxyapatite by Carboxylic Acids

Abstract: Fundamental to the processes of decalcification of or adhesion to mineralized tissues is the molecular interaction of acids with hydroxyapatite. This study was undertaken to chemically analyze the interaction of 1 mono-, 2 di-, 1 tri-, and 2 polycarboxylic acids with hydroxyapatite in an attempt to elucidate the underlying mechanism. Maleic, citric, and lactic acid decalcified hydroxyapatite, in contrast to oxalic acid and the two polycarboxylic acids that were chemically bonded to hydroxyapatite. Solubility tests showed that the calcium salts of the former were very soluble, whereas those of the latter could hardly be dissolved in the respective acid solutions. Based on these data, an adhesion/decalcification concept was advanced that predicts that carboxylic acids, regardless of concentration/pH, either adhere to or decalcify hydroxyapatite, depending on the dissolution rate of the respective calcium salts in the acid solution. This contrasting behavior of organic acids most likely results from their differential structural conformations.

Degradation behaviors of biodegradable macroporous scaffolds prepared by gas foaming of effervescent salts.

Abstract: Biodegradable polymeric scaffolds for tissue engineering were fabricated by a gas-foaming/salt-leaching method using a combination of two effervescent salts, ammonium bicarbonate and citric acid. Poly(D,L-lactic-co-glycolic acid) (PLGA) in a state of gel-like paste was first produced by precipitation of PLGA dissolved in chloroform into ethanol. The polymer slurry was mixed with sieved particles of ammonium bicarbonate, molded, and then immersed in an aqueous solution of citric acid to generate macroporous scaffolds. The scaffolds had relatively homogeneous pore structures throughout the matrix and showed an average pore size of 200 μm and over 90% porosity. By adjusting the concentration of citric acid in the aqueous medium, it was possible to control porosity as well as mechanical strength of the scaffolds. In vitro degradation studies of three different scaffolds having lactic/glycolic acid molar ratios of 75/25, 65/35, and 50/50 exhibited marked swelling behaviors at different critical time points. The swollen matrices had a hydrogel-like internal structure. It was found that massive water uptake into the degrading scaffolds induced matrix swelling, which facilitated the hydrolytic scission of PLGA chains with concomitant disintegration of the matrices. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 55: 401–408, 2001

Expression of a Pseudomonas aeruginosa citrate synthase gene in tobacco is not associated with either enhanced citrate accumulation or efflux.

Abstract: Aluminum (Al) toxicity and poor phosphorus (P) availability are factors that limit plant growth on many agricultural soils. Previous work reported that expression of a Pseudomonas aeruginosa citrate synthase gene in tobacco (Nicotiana tabacum; CSb lines) resulted in improved Al tolerance (J.M. de la Fuente, V. Ramirez-Rodriguez, J.L. Cabrera-Ponce, L. Herrera-Estrella [1997] Science 276: 1566-1568) and an enhanced ability to acquire P from alkaline soils (J. Lopez-Bucio, O. Martinez de la Vega, A. Guevara-Garcia, L. Herrera-Estrella [2000] Nat Biotechnol 18: 450-453). These effects were attributed to the P. aeruginosa citrate synthase increasing the biosynthesis and efflux of citrate from roots. To verify these findings we: (a) characterized citrate efflux from roots of wild-type tobacco; (b) generated tobacco lines expressing the citrate synthase gene from P. aeruginosa; and (c) analyzed selected CSb lines described above. Al stimulated citrate efflux from intact roots of wild-type tobacco and root apices were found to be responsible for most of the efflux. Despite generating transgenic tobacco lines that expressed the citrate synthase protein at up to a 100-fold greater level than the previously described CSb lines, these lines did not show increased accumulation of citrate in roots or increased Al-activated efflux of citrate from roots. Selected CSb lines, similarly, failed to show differences compared with controls in either citrate accumulation or efflux. We conclude that expression of the P. aeruginosa citrate synthase gene in plants is unlikely to be a robust and easily reproducible strategy for enhancing the Al tolerance and P-nutrition of crop and pasture species.

Aluminum Activates a Citrate-Permeable Anion Channel in the Aluminum-Sensitive Zone of the Maize Root Apex. A Comparison Between an Aluminum- Sensitive and an Aluminum-Resistant Cultivar

Abstract: In search for the cellular and molecular basis for differences in aluminum (Al) resistance between maize ( Zea mays ) cultivars we applied the patch-clamp technique to protoplasts isolated from the apical root cortex of two maize cultivars differing in Al resistance. Measurements were performed on protoplasts from two apical root zones: The 1- to 2-mm zone (DTZ), described as most Al-sensitive, and the main elongation zone (3–5 mm), the site of Al-induced inhibition of cell elongation. Al stimulated citrate and malate efflux from intact root apices, revealing cultivar differences. In the elongation zone, anion channels were not observed in the absence and presence of Al. Preincubation of intact roots with 90 μmAl for 1 h induced a citrate- and malate-permeable, large conductance anion channel in 80% of the DTZ protoplasts from the resistant cultivar, but only 30% from the sensitive cultivar. When Al was applied to the protoplasts in the whole-cell configuration, anion currents were elicited within 10 min in the resistant cultivar only. La 3+ was not able to replace or counteract with Al 3+ in the activation of this channel. In the presence of the anion-channel blockers, niflumic acid and 4, 4′-dinitrostilbene-2, 2′disulfonic acid, anion currents as well as exudation rates were strongly inhibited. Application of cycloheximide did not affect the Al response, suggesting that the channel is activated through post-translational modifications. We propose that the Al-activated large anion channel described here contributes to enhanced genotypical Al resistance by facilitating the exudation of organic acid anions from the DTZ of the maize root apex.

The effect of pH on the erosion of dentine and enamel by dietary acids in vitro

Abstract: The reported incidence of tooth erosion caused by acidic soft drinks has been increasingly documented. Citric and phosphoric acids are the two main dietary acids present in these soft drinks. Many variables need to be determined in order to assess risk factors for dental erosion caused by beverage consumption including pH, titratable acidity, pKa, buffering capacity, hence the aim of these in vitro investigations. Methodologies included profiling flat enamel and dentine samples (< +/- 0.3 microm profile) from unerupted human third molars. Groups of five specimens were placed in acidic solutions adjusted with alkali over the available pH range; citric, phosphoric and hydrochloric acid were adjusted with sodium hydroxide and citric acid with trisodium citrate. Tissue loss was calculated by profilometry. Results showed that under these conditions citric acid caused far more erosion over the pH range employed than phosphoric acid for both tissue types. Citric acid compared with hydrochloric acid highlighted dissolution and chelation effects. Phosphoric acid caused minimal erosion over pH 3 for enamel and pH 4 for dentine. These factors could be considered in order to reduce the erosivity of acidic soft drinks.

Differential aluminum tolerance in soybean: An evaluation of the role of organic acids.

Abstract: The role of organic acids in aluminum (Al) tolerance has been the object of intensive research In the present work, we evaluated the roles of organic acid exudation and concentrations at the root tip on Al tolerance of soybean Exposing soybean seedlings to Al 3 + activities up to 47 μM in solution led to different degrees of restriction of primary root elongation Al tolerance among genotypes was associated with citrate accumulation and excretion into the external media Citrate and malate efflux increased in all genotypes during the first 6 h of Al exposure, but only citrate efflux in Al-tolerant genotypes was sustained for an extended period Tolerance to Al was correlated with the concentration of citrate in root tips of 8 genotypes with a range of Al sensitivities (r 2 = 075) The fluorescent stain lumogallion indicated that more Al accumulated in root tips of the Al-sensitive genotype Young than the Al-tolerant genotype PI 416937, suggesting that the sustained release of citrate from roots of the tolerant genotype was involved in Al exclusion The initial stimulation of citrate and malate excretion and accumulation in the tip of all genotypes suggested the involvement of additional tolerance mechanisms The experiments included an examination of Al effects on lateral root elongation Extension of lateral roots was more sensitive to Al than that of tap roots, and lateral root tips accumulated more Al and had lower levels of citrate

Heterofermentative pattern and exopolysaccharide production by Lactobacillus helveticus ATCC 15807 in response to environmental pH.

Abstract: Aims: The objective of this work was to evaluate the fermentation pattern of and the exopolysaccharide (EPS) production by Lactobacillus helveticus ATCC 15807 in milk batch cultures under controlled pH (4·5, 5·0 and 6·2). Methods and Results: EPS concentration was estimated by the phenol/sulphuric acid method and the chemical composition of purified EPS by HPLC. Fermentation products and residual sugars were determined by HPLC and enzymatic methods. The micro-organism shifted from a homofermentative to a heterofermentative pattern, producing acetate (9·5 and 5·8 mmol l–1) at pH 5·0 and 6·2, respectively, and acetate (7·1 mmol l–1) plus succinate (1·2 mmol l–1) at pH 4·5. At pH 5·0 and 6·2, acetate derived from citrate while at pH 4·5 it came from both citrate and pyruvate splitting. The EPS has a MW of 105–106 and contains phosphate (81% in average), rhamnose (traces), and glucose and galactose in a ratio of 1 : 1 (pH 6·2) and 2 : 1 (pH 4·5 and 5·0). The highest production (549 mg l–1) corresponded to pH 5·0 and the lowest (49 mg l–1) to pH 6·2. Conclusions: The heterofermentative pattern of Lact. helveticus ATCC 15807 was linked to alternative pyruvate pathways and/or citrate metabolism according to the environmental pH. The EPS production was improved under low environmental pH conditions. Significance and Impact of the Study: This work provides relevant information of the effect of pH on the metabolism of citrate and EPS production by Lact. helveticus. It may contribute to improve technological aspects of ropy and citrate-utilizing lactic acid bacteria.

Extraction of Gelatin from Megrim (Lepidorhombus boscii) Skins with Several Organic Acids

Abstract: Light-colored, dry collagen was obtained and, after dissolving in warm water, turned into soluble gelatin The type of acid used influenced the gelatin viscoelastic and gelling properties Acetic- and propionic-acid extracts produced the gelatins with the highest elastic modulus, viscous modulus, melting temperature, and gel strength, especially when skins were previously treated with dilute NaOH After such treatment, lactic acid was also shown to be suitable for collagen or gelatin extraction The lowest degree of turbidity was achieved by using citric acid, whereas propionic acid led to the most turbid gelatin No improvements of rheological properties were observed when acid concentration for extraction was increased above 005 M

Solubilization of phosphate rocks and minerals by a wild-type strain and two UV-induced mutants of Penicillium rugulosum

Abstract: Two Venezuelan phosphate rocks (PRs), apatite deposits from Monte-Fresco and Navay areas, and two minerals, Florida apatite and Utah variscite were used to investigate phosphate solubilization by the wild type strain IR-94MF1 of Penicillium rugulosum initially selected for its high mineral phosphate activity (Mps + ) and two of its mutants Mps ++ and Mps − . In liquid cultures, the three fungal strains showed better growth on the Navay PR than on Monte Fresco PR. The Utah variscite was the best phosphorus (P) source for the growth of the wild type and the Mps ++ mutant. Solubilization of the various P sources by the wild-type IR-94MF1 and the Mps ++ mutant resulted mostly from the action of organic acids. Citric acid seemed to be more active agent for the solubilization of the Utah variscite while gluconic acid appeared to be responsible for the solubilization of the Florida apatite and the Monte Fresco PR. Both organic acids are likely involved in the solubilization of the Navay PR. The Mps - mutant did not produce any organic acid when grown on all the P sources used.

Mutation of Aspergillus niger for hyperproduction of citric acid from black strap molasses

Abstract: Spore suspensions of Aspergillus niger GCB 75, which produced 31.1 g/l citric acid from 15% sugars in molasses, were subjected to u.v.-induced mutagenesis. Among three variants, GCM 45 was found to be the best citric acid producer and was further improved by chemical mutagenesis using NTG. Out of 3 deoxy-D-glucose-resistant variants, GCM 7 was selected as the best mutant which produced 86.1 ± 1.5 g/l citric acid after 168 h of fermentation of potassium ferricyanide + H2SO4-pretreated black strap molasses (containing 150 g sugars/l) in Vogel's medium. On the basis of comparison of kinetic parameters, namely the volumetric substrate uptake rate (Qs), and specific substrate uptake rate (qs), the volumetric productivity, theoretical yield and specific product formation rate, it was observed that the mutants were faster growing organisms and had the ability to overproduce citric acid.

Complexation effect of antimony compounds with citric acid and its application to the speciation of antimony(III) and antimony(V) using HPLC-ICP-MS

Abstract: In this work, a complexation effect of Sb compounds with citric acid was observed using electrospray mass spectrometry (ES-MS). It was found that both Sb(III) and Sb(V) could form complexes readily with citric acid in an aqueous solution at room temperature. These complexes were found to be very stable in various matrices (moat water and aqueous extracts of airborne particulate matter), therefore, a novel HPLC-ICP-MS analytical method for the speciation of Sb(III) and Sb(V) in environmental samples was developed by using the observed complexation effect. Sb(III)- and Sb(V)-citrate complexes were separated on a PRP-X100 anion-exchange column with 10 mmol l−1 EDTA–1 mmol l−1 phthalic acid (pH 4.5) as a mobile phase. All complexes were retained on the separation column, and none of them eluted in the solvent front. Low detection limits of 0.05 µg l−1 and 0.07 µg l−1 were achieved for Sb(III) and Sb(V), respectively. The calibration curves were linear over the range of 1.0–250 µg l−1 for the investigated Sb species. The precisions, evaluated by using the relative standard deviation (%RSD) with a 2 µg l−1 standard solution, were 1.8% and 3.3% for Sb(III) and Sb(V), respectively. Several advantages of the developed method, such as improving chromatographic separation, stabilizing Sb compounds in a water sample, and preventing Sb(III) from oxidizing to Sb(V) during the ultrasonic-assisted and microwave-assisted extraction of an airborne particulate matter (APM) sample using 26 mmol l−1 citric acid as an extraction solvent, and alleviating the adsorption of Sb compounds on the sample surface, were observed. The developed method enabled us to detect the most toxic Sb specie, Sb(III), in an APM sample for the first time.

Optimizing medium constituents and fermentation conditions for citric acid production from palmyra jaggery using response surface method

Abstract: The quantitative effects of pH, temperature, time of fermentation, sugar concentration, nitrogen concentration and potassium ferrocyanide on citric acid production were investigated using a statistical experimental design. It was found that palmyra jaggery (sugar syrup from the palmyra palm) is a suitable substrate for increasing the yield of citric acid using Aspergillus niger MTCC 281 by submerged fermentation. Regression equations were used to model the fermentation in order to determine optimum fermentation conditions. Higher yields were obtained after optimizing media components and conditions of fermentation. Maximum citric acid production was obtained at pH 5.35, 29.76 °C, 5.7 days of fermentation with 221.66 g of substrate/l, 0.479 g of ammonium nitrate/l and 2.33 g of potassium ferrocyanide/l.

The influence of marinating with weak organic acids and salts on the intramuscular connective tissue and sensory properties of beef

Abstract: Longissimus dorsi muscles obtained from middle-aged bovine carcasses were used in this project. Initially, 2%, 4%, and 6% NaCl, 50 mM, 100 mM, and 150 mM CaCl2, and 0.5%, 1.0%, and 1.5% lactic and citric acids solutions were prepared and then treated 1:1 with (w/v) meat pieces in polyethylene bags at 4 °C for 24 h for marinating. Some physical and organoleptical changes in the meat treated with the above-mentioned solutions were determined. According to control samples, the highest lightness (L*) value was found in meat marinated with CaCl2 while the lowest L* value was in meat marinated with lactic acid. No positive correlation was found between penetrometer values and tenderness except in meat treated with lactic acid. Panel tests showed that all procedures increased tenderness and juiciness to a certain extent. All concentrations of NaCl and CaCl2 had a positive effect on taste and aroma of meat while acid concentrations up to 1.0% were acceptable. Increased water binding capacity was found in all samples. Electrophoresis of connective tissue proteins obtained from the same muscle showed that NaCl and CaCl2 did not cause any change in the structure, but that both lactic and citric acid increased tissue breakdown.

Combined effect of ascorbic acid and gamma irradiation on microbial and sensorial characteristics of beef patties during refrigerated storage.

Abstract: The present study was undertaken to evaluate the effect of ascorbic acid concentrations (0.03 to 0.5%) and irradiation doses (0.5 to 4 kGy) on microbial growth, color coordinates (L, a, and b), and sensory characteristics (taste and odor) of beef patties during storage at 4 +/- 1 degrees C. Ascorbic acid was also compared to citric acid at a similar pH value in order to differentiate the effects of ascorbic acid from those of pH reduction. Results showed significant reduction (p< or = 0.05) of aerobic plate counts (APCs) and total coliforms, and a significant interaction (p< or = 0.05) between ascorbic acid and irradiation dose was observed. The irradiation treatment had detrimental effects on redness, yellowness, and hue angle values of meat. However, incorporation of ascorbic acid into the meat before irradiation resulted in significant (p< or = 0.05) stabilization of color parameters. The color improvement obtained with ascorbic acid was not related to the pH reduction. Also, no significant detrimental effect on taste or odor was found in irradiated samples containing ascorbic acid.

Partial purification and characterization of polyphenol oxidase from banana (Musa sapientum L.) peel.

Abstract: Polyphenol oxidase (EC 11031, o-diphenol: oxygen oxidoreductase, PPO) of banana (Musa sapientum L) peel was partially purified about 460-fold with a recovery of 22% using dopamine as substrate The enzyme showed a single peak on Toyopearl HW55-S chromatography However, two bands were detected by staining with Coomassie brilliant blue on PAGE: one was very clear, and the other was faint Molecular weight for purified PPO was estimated to be about 41 000 by gel filtration The enzyme quickly oxidized dopamine, and its Km value (Michaelis constant) for dopamine was 39 mM Optimum pH was 65 and the PPO activity was quite stable in the range of pH 5-11 for 48 h The enzyme had an optimum temperature at 30 degrees C and was stable up to 60 degrees C after heat treatment for 30 min The enzyme activity was strongly inhibited by sodium diethyldithiocarbamate, potassium cyanide, L-ascorbic acid, and cysteine at 1 mM Under a low buffer capacity, the enzyme was also strongly inhibited by citric acid and acetic acid at 10 mM