Showing papers on "Citric acid published in 1999"
TL;DR: The physiology and chemistry of citric and oxalic acid production in fungi are discussed, the intimate association of these acids and processes with metal speciation, physiology and mobility, and their importance and involvement in key fungal-mediated processes, including lignocellulose degradation, plant pathogenesis and metal biogeochemistry.
Abstract: The production of organic acids by fungi has profound implications for metal speciation, physiology and biogeochemical cycles. Biosynthesis of oxalic acid from glucose occurs by hydrolysis of oxaloacetate to oxalate and acetate catalysed by cytosolic oxaloacetase, whereas on citric acid, oxalate production occurs by means of glyoxylate oxidation. Citric acid is an intermediate in the tricarboxylic acid cycle, with metals greatly influencing biosynthesis: growth limiting concentrations of Mn, Fe and Zn are important for high yields. The metal-complexing properties of these organic acids assist both essential metal and anionic (e.g. phosphate) nutrition of fungi, other microbes and plants, and determine metal speciation and mobility in the environment, including transfer between terrestrial and aquatic habitats, biocorrosion and weathering. Metal solubilization processes are also of potential for metal recovery and reclamation from contaminated solid wastes, soils and low-grade ores. Such ‘heterotrophic leaching’ can occur by several mechanisms but organic acids occupy a central position in the overall process, supplying both protons and a metal-complexing organic acid anion. Most simple metal oxalates [except those of alkali metals, Fe(III) and Al] are sparingly soluble and precipitate as crystalline or amorphous solids. Calcium oxalate is the most important manifestation of this in the environment and, in a variety of crystalline structures, is ubiquitously associated with free-living, plant symbiotic and pathogenic fungi. The main forms are the monohydrate (whewellite) and the dihydrate (weddelite) and their formation is of significance in biomineralization, since they affect nutritional heterogeneity in soil, especially Ca, P, K and Al cycling. The formation of insoluble toxic metal oxalates, e.g. of Cu, may confer tolerance and ensure survival in contaminated environments. In semiarid environments, calcium oxalate formation is important in the formation and alteration of terrestrial subsurface limestones. Oxalate also plays an important role in lignocellulose degradation and plant pathogenesis, affecting activities of key enzymes and metal oxidoreduction reactions, therefore underpinning one of the most fundamental roles of fungi in carbon cycling in the natural environment. This review discusses the physiology and chemistry of citric and oxalic acid production in fungi, the intimate association of these acids and processes with metal speciation, physiology and mobility, and their importance and involvement in key fungal-mediated processes, including lignocellulose degradation, plant pathogenesis and metal biogeochemistry.
644 citations
TL;DR: The results suggest that P deficiency-induced exudation of carboxylic acids depends on the ability to accumulate carboxYlic acids in the root tissue, which in turn is determined by biosynthesis, degradation and partitioning of car boxylic acid or related precursors between roots and shoot.
Abstract: Phosphorus deficiency-induced metabolic changes related to exudation of carboxylic acids and protons were compared in roots of wheat (Triticum aestivum L. cv Haro), tomato (Lycopersicon esculentum L., cv. Moneymaker), chickpea (Cicer arietinum) and white lupin (Lupinus albus L. cv. Amiga), grown in a hydroponic culture system. P deficiency strongly increased the net release of protons from roots of tomato, chickpea and white lupin, but only small effects were observed in wheat. Release of protons coincided with increased exudation of carboxylic acids in roots of chickpea and white lupin, but not in those of tomato and wheat. P deficiency-induced exudation of carboxylic acids in chickpea and white lupin was associated with a larger increase of carboxylic acid concentrations in the roots and lower accumulation of carboxylates in the shoot tissue compared to that in wheat and tomato. - Citric acid was one of the major organic acids accumulated in the roots of all investigated species in response to P deficiency, and this was associated with increased activity and enzyme protein levels of PEP carboxylase, which is required for biosynthesis of citrate. Accumulation of citric acid was most pronounced in the roots of P-deficient white lupin, chickpea and tomato. Increased PEP carboxylase activity in the roots of these plants coincided with decreased activity of aconitase, which is involved in the breakdown of citric acid in the TCA cycle. In the roots of P-deficient wheat plants, however, the activities of both PEP carboxylase and aconitase were enhanced, which was associated with little accumulation of citric acid. The results suggest that P deficiency-induced exudation of carboxylic acids depends on the ability to accumulate carboxylic acids in the root tissue, which in turn is determined by biosynthesis, degradation and partitioning of carboxylic acids or related precursors between roots and shoot. In some plant species such as white lupin, there are indications for a specific transport mechanism (anion channel), involved in root exudation of extraordinary high amounts of citric acid.
570 citations
TL;DR: It is demonstrated that increased accumulation and exudation of citric acid and a concomitant release of protons were predominantly restricted to mature root clusters in the later stages of P deficiency, suggesting the induction of a high-affinity Pi-uptake system.
Abstract: Release of large amounts of citric acid from specialized root clusters (proteoid roots) of phosphorus (P)-deficient white lupin (Lupinus albus L.) is an efficient strategy for chemical mobilization of sparingly available P sources in the rhizosphere. The present study demonstrates that increased accumulation and exudation of citric acid and a concomitant release of protons were predominantly restricted to mature root clusters in the later stages of P deficiency. Inhibition of citrate exudation by exogenous application of anion-channel blockers such as ethacrynic- and anthracene-9-carboxylic acids may indicate involvement of an anion channel. Phosphorus-deficiency-induced accumulation and subsequent exudation of citric acid seem to be a consequence of both increased biosynthesis and reduced metabolization of citric acid in the proteoid root tissue, indicated by increased in-vitro activity and enzyme protein levels of phosphoenolpyruvate carboxylase (EC 4.1.1.31), and reduced activity of aconitase (EC 4.2.1.3) and root respiration. Similar to citric acid, acid phosphatase, which is secreted by roots and involved in the mobilization of the organic soil P fraction, was released predominantly from proteoid roots of P-deficient plants. Also 33Pi uptake per unit root fresh-weight was increased by approximately 50% in juvenile and mature proteoid root clusters compared to apical segments of non-proteoid roots. Kinetic studies revealed a K
m of 30.7 μM for Pi uptake of non-proteoid root apices in P-sufficient plants, versus K
m values of 8.5–8.6 μM for non-proteoid and juvenile proteoid roots under P-deficient conditions, suggesting the induction of a high-affinity Pi-uptake system. Obviously, P-deficiency-induced adaptations of white lupin, involved in P acquisition and mobilization of sparingly available P sources, are predominantly confined to proteoid roots, and moreover to distinct stages during proteoid root development.
424 citations
TL;DR: In this article, the rank order of mineral potency as inhibitors of phytate hydrolysis was Zn 2+ ⪢Fe 2+ >Mn 2+) >Fe 3+ >Ca 2+>Mg 2+ at neutral pH.
255 citations
TL;DR: Results suggest that acetate has the maximum molecular volume above which the film strength decreases very rapidly, which is essentially governed by the volume of thecounter ion and not by the interactions between this counter ion and the macromolecule.
234 citations
TL;DR: A strain lacking both glucose oxidase (goxC) and OAH (prtF) produced citric acid from sugar substrates in a regular synthetic medium at pH 5 and under these conditions production was completely insensitive to Mn2+.
Abstract: The external pH appeared to be the main factor governing oxalic acid production by Aspergillus niger. A glucose-oxidase-negative mutant produced substantial amounts of oxalic acid as long as the pH of the culture was 3 or higher. When pH was decreased below 2, no oxalic acid was formed. The activity of oxaloacetate acetylhydrolase (OAH), the enzyme believed to be responsible for oxalate formation in A. niger, correlated with oxalate production. OAH was purified from A. niger and characterized. OAH cleaves oxaloacetate to oxalate and acetate, but A. niger never accumulated any acetate in the culture broth. Since an A. niger acuA mutant, which lacks acetyl-CoA synthase, did produce some acetate, wild-type A. niger is apparently able to catabolize acetate sufficiently fast to prevent its production. An A. niger mutant, prtF28, previously isolated in a screen for strains deficient in extracellular protease expression, was shown here to be oxalate non-producing. The prtF28 mutant lacked OAH, implying that OAH is the only enzyme involved in oxalate production in A. niger. In a traditional citric acid fermentation low pH and absence of Mn2+ are prerequisites. Remarkably, a strain lacking both glucose oxidase (goxC) and OAH (prtF) produced citric acid from sugar substrates in a regular synthetic medium at pH 5 and under these conditions production was completely insensitive to Mn2+.
214 citations
TL;DR: In this paper, the root-induced changes in the soil affecting phosphate solubility were measured, and the extent to which the observed excretion of citrate and rootinduced pH changes could account for the observed phosphorus solubilization and uptake was assessed using a mathematical model.
Abstract: Rice (Oryza sativa) plants were grown with their roots sandwiched between thin layers of phosphorus-deficient soil from which they were separated by fine mesh, and root-induced changes in the soil affecting phosphate solubility were measured. The concentrations of low molecular weight organic anions in the thin layers, particularly citrate, increased in the presence of the plants. Apparent rates of citrate excretion from the roots, calculated from the quantities in the soil and rates of decomposition calculated with a first order rate constant measured independently, varied from 337–155 nmol g−1 root f. wt h−1 over the course of plant growth, equivalent to 2–3% of plant d. wt. Rates of excretion were similar for NH4+ and NO3−-fed plants. The soil pH decreased from its initial value by up to 0.6 units for the NH4+-fed plants and increased by up to 0.4 units for the NO3−-fed ones. The contribution of organic anion excretion to the pH changes was small compared with that of the inorganic cation-anion balance in the plants. The extent to which the observed excretion of citrate and root-induced pH changes could account for the observed phosphate solubilization and uptake was assessed using a mathematical model. Previous work had shown that phosphate solubilization by rice in this soil could not be explained by enhanced phosphatase activity in the rhizosphere, and the roots were not infected with mycorrhizas. The model allows for the diffusion of the solubilizing agent (citrate or H+) away from the roots, its decomposition by soil microbes (citrate only); its reaction with the soil in solubilizing phosphate and diffusion of the solubilized phosphate to the roots. The model contains no arbitrary assumptions and uses only independently measured parameter values. The agreement between the measured time course of phosphorus uptake and that predicted for solubilization by citrate was good. Root-induced acidification by NH4+-fed plants resulted in additional solubilization, the acidification enhancing the solubilizing effect of citrate. However, the final phosphorus uptake by NH4+-fed plants was no greater than that of NO3−-fed plants, presumably because the acidification inhibited plant growth. The mechanism of solubilization by citrate involved formation of soluble metal-citrate chelates rather than displacement of phosphate from adsorption sites.
150 citations
TL;DR: The role of citric acid in a simulated body fluid (SBF) was examined with the main focus on its induction ability of hydroxyapatite (HAp) nucleation on a bioinert collagen membrane, especially strong chelation ability ofcitric acid with the calcium ion.
149 citations
TL;DR: The maximum concentration of diacetyl obtained during malolactic fermentation was strongly dependent on the oxygen concentration and the redox potential of the wine and, to a lesser extent, on the initial citric acid concentration.
Abstract: During malolactic fermentation in wine by Oenococcus oeni, the degradation of citric acid was delayed compared to the degradation of malic acid. The maximum concentration of diacetyl, an intermediary compound in the citric acid metabolism with a buttery or nutty flavor, coincided with the exhaustion of malic acid in the wine. The maximum concentration of diacetyl obtained during malolactic fermentation was strongly dependent on the oxygen concentration and the redox potential of the wine and, to a lesser extent, on the initial citric acid concentration. The final diacetyl concentration in the wine was also dependent on the concentration of SO2. Diacetyl combines rather strongly with SO2 (Kf = 7.2 × 103 M−1 in 0.1 M malate buffer [pH 3.5] at 30°C). The reaction is exothermic and reversible. If the concentration of SO2 decreases during storage of the wine, the diacetyl concentration increases again.
145 citations
TL;DR: In this article, the adsorption ability of Cu(II) using chitosan from simulated rinse solutions containing chelating agents was studied, and the maximum adaption capacity was found within each optimal pH range.
128 citations
TL;DR: It is concluded that citric acid-induced bronchoconstriction is caused by tachykinin release from sensory nerves, which, in part, is mediated by endogenously released bradykinin.
Abstract: 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 (R L ). R L value obtained after 10 breaths of citric acid inhalation was not significantly different from the value obtained after 20 breaths (p 5 0.22). The effect produced by a half-submaximum dose of citric acid (5 breaths) was halved by the bradykinin B 2 receptor antagonist HOE 140 (0.1 m mol ? kg 2 1 , intravenous) and abolished by the tachykinin NK 2 receptor antagonist SR 48968 (0.3 m mol ? kg 2 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 NK 1 receptor antagonist CP-99,994 (8 m mol ? kg 2 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 R L . HOE 140 and CP99,994 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. Ricciardolo FLM, Rado V, Fabbri LM, Sterk PJ, Di Maria GU, Geppetti P. Bronchoconstriction induced by citric acid inhalation in guinea pigs: role of tachykinins, bradykinin, and nitric oxide. AM J RESPIR CRIT CARE MED 1999;159:557‐562. Gastroesophageal acid reflux is more common in patients with asthma than in the general population, with an estimated
TL;DR: In this article, the authors present a brief summary of the recent developments on citric acid production, describing micro-organisms, production techniques, and substrates, etc., and describe the most important organic acid produced in tonnage and extensively used in food and pharmaceutical industries.
Abstract: Citric acid is the most important organic acid produced in tonnage and is extensively used in food and pharmaceutical industries. It is produced mainly by submerged fermentation using Aspergillus niger or Candida sp. from different sources of carbohydrates, such as molasses and starch based media. However, other fermentation techniques, e.g. solid state fermentation and surface fermentation, and alternative sources of carbon such as agro-industrial residues have been intensively studied showing great perspective to its production. This paper reviews recent developments on citric acid production by presenting a brief summary of the subject, describing micro-organisms, production techniques, and substrates, etc.
TL;DR: In this article, the role of pH in adsorption of Cu(II) from aqueous solutions containing chelating agents on chitosan was emphasized, and the maximum adaption capacity was obtained within each optimal pH range determined from titration curves of the chelated solutions.
Abstract: The role of pH in adsorption of Cu(II) from aqueous solutions containing chelating agents on chitosan was emphasized. Four chelating agents including ethylenediaminetetraacetic acid (EDTA), citric acid, tartaric acid, and sodium gluconate were used. It was shown that the adsorption ability of Cu(II) on chitosan from its chelated solutions varied significantly with pH variations. The competition between coordination of Cu(II) with unprotonated chitosan and electrostatic interaction of the Cu(II) chelates with protonated chitosan took place because of the change in solution pH during adsorption. The maximum adsorption capacity was obtained within each optimal pH range determined from titration curves of the chelated solutions. Coordination of Cu(II) with the unprotonated chitosan was found to dominate at pH below such an optimal pH value.
TL;DR: The addition of 6% (w/w) methanol into the substrate increased the concentration of citric acid from 176 to 264 g kg−1 dry pod, and the maximum citricacid concentration was obtained at a particle size of 0.5 mm.
TL;DR: The bioavailability of dietary P can be improved by fine grinding the bone in fish meals, and dietary acidification by citric acid significantly increased whole-body iron in a linear fashion.
Abstract: Juvenile rainbow trout Oncorhynchus mykiss (Walbaum) were fed six low-phosphorus (P) diets supplemented with two different sizes of ground fish bone-meals (fine, 68 μm or less; coarse, 250–425 μm) and a coarse bone-meal diet containing four levels of citric acid (0, 4, 8 or 16 g kg−1 diet) to investigate the effects of pH and bone particle size on P bioavailability The basal diet provided 34 g P kg−1 and bone-meal increased P contents to 54–60 g P kg−1 Coarse bone-meal diets supplemented with 0, 4, 8 or 16 g kg−1 of citric acid had pH values of 60, 57, 54 and 50, respectively Weight gain and whole-body water, protein and lipid contents were not influenced by bone-meal supplementation Supplementing the basal diet with both coarse and fine bone-meal significantly increased whole-body ash content Fish fed no bone-meal were hypophosphataemic compared with fish fed with either fine or coarse bone-meals Phosphorus in fine bone-meal had higher availability than P in coarse bone-meal Bone-meal supplementation significantly decreased whole-body manganese content from 89 μg g−1 in fish fed no bone-meal to 23 and 45 μg g−1 in fish fed with fine and coarse bone-meals, respectively The concentration of magnesium increased but zinc concentration was not affected by bone-meal supplements Citric acid increased whole-body ash content but the influence of citric acid on the body P content was not significant (P = 007) Dietary acidification by citric acid significantly increased whole-body iron in a linear fashion The bioavailability of dietary P can be improved by fine grinding the bone in fish meals
TL;DR: It is shown that organic acids differ in their inhibitory or lethal activity against acid- Adapted and unadapted E. coli O157:H7 cells, and acid-adapted cells are more tolerant than un Adapted cells when subsequently exposed to reduced pH caused by these acids.
TL;DR: Feed-batch (glucostat) experiments were used to eliminate the effects of decreasing sugar concentration found during conventional batch experiments and confirmed that initial glucose concentration in the fermentation medium affected both the rate of citric acid fermentation by Aspergillus niger and the morphology of the producer micro-organism.
TL;DR: Results support previous qualitative ideas that initial inoculum morphology and fermentation conditions have significant effects on the subsequent culture morphology and productivity of the citric acid fermentation.
TL;DR: A fast and reproducible reverse-phase high-performance liquid chromatography (HPLC) assay method has been developed for the simultaneous quantitation of omeprazole, lansoprazoles, and pantoprazole to study the effect of pH and various salts on the stability of the three compounds.
Abstract: A fast and reproducible reverse-phase high-performance liquid chromatography (HPLC) assay method has been developed for the simultaneous quantitation of omeprazole, lansoprazole, and pantoprazole. The three compounds were monitored at 280 nm using Zorbax Eclipse XDB C8 (5 μm, 150 cm × 4.6 mm i.d.) and a mobile phase consisting of 700:300 phosphate buffer:acetonitrile with the pH adjusted to 7.0 with phosphoric acid. The method was used to study the effect of pH and various salts on the stability of the three compounds. The pH rate profile curve showed that pantoprazole was the most stable compound and lansoprazole the least stable. The stabilities of the compounds in salt solutions were found to be in the following order: phosphate buffer < trisodium citrate < citrate buffer ≤ acetate buffer < citric acid ≤ monosodium citrate ≤ calcium carbonate < sodium bicarbonate < sodium chloride < water. The rate of degradation had a direct relationship with the H+ and salt concentration.
TL;DR: The data are consistent with the marked effect of citric acid on gastric emptying and, possibly, distribution of the urea within the stomach being largely responsible for the enhanced urease activity with citric Acid test meals.
TL;DR: Gypsum solubilization was predominantly achieved by both oxalic acid, which was accompanied by formation of calcium oxalate crystals, and citric acid production rather than the acidity of the medium, as well as the possible roles played by these fungi in mineral cycling.
TL;DR: There was essentially no difference in growth characteristics of the two types of cells in TSB acidified at the same pH with a given acid, and on plates not showing visible colonies, acid‐ Adapted cells retained higher viability than unadapted cells when plated on acidified TSA.
Abstract: A study was carried out to determine if three strains of Escherichia coli O157:H7 grown (18 h) in Tryptic Soy Broth (TSB) and TSB supplemented with 1.25% glucose (TSBG), i.e. unadapted and acid-adapted cells, respectively, exhibited changes in tolerance to reduced pH when plated on Tryptic Soy Agar (TSA) acidified (pH 3.9, 4.2, 4.5, 4.8, 5.1 and 5.4) with acetic, citric or malic acids. All test strains grew well on TSA acidified with acetic acid at pH > or = 5.4 or malic acid at pH > or = 4.5; two strains grew on TSA acidified with citric acid at pH > or = 4.5, while the third strain grew at pH > or = 4.8. Acid-adapted and control (unadapted) cells differed little in their ability to form visible colonies on TSA containing the same acid at the same pH. However, on plates not showing visible colonies, acid-adapted cells retained higher viability than unadapted cells when plated on acidified TSA. Growth of acid-adapted and control cells of E. coli O157:H7 inoculated into TSB containing acetic acid (pH 5.4 and 5.7) and citric or malic acids (pH 4.2 and 4.5) was also studied. There was essentially no difference in growth characteristics of the two types of cells in TSB acidified at the same pH with a given acid. Tolerance of acid-adapted and control cells on subsequent exposure to low pH is influenced by the type of acidulant. The order of sensitivity at a given pH is acetic > citric > malic acid. When performing acid challenge studies to determine survival and growth characteristics of E. coli O157:H7 in foods, consideration should be given to the type of acid to which cells have been exposed previously, the procedure used to achieve acidic environments and possible differences in response among strains. The use of strains less affected by pH than type of acidulant or vice versa could result in an underestimation of the potential for survival and growth of E. coli O157:H7 in acid foods.
TL;DR: In this paper, the synthesis of layered LiNi0.6Co0.4O2 powders using citric acid as a chelating agent has been described, and the synthesized products have been characterized by structural (XRD, SEM), spectroscopic (FTIR, Raman) and thermal (DTA/TG) analyses.
Abstract: The layered LiNi0.6Co0.4O2 powders were synthesized at low temperature by a sol-gel method using citric acid as a chelating agent. Submicron-sized particles of the precursor were obtained at temperature below 400°C and microcrystalline powders were grown by thermal treatment at 700°C for 4 h in air. The carboxylic-based acid acted such as a fuel, decomposed the homogeneous precipitate of metal complexes at low temperature, and yielded the free impurity LiNi0.6Co0.4O2 single-phase suitable for electrochemical application. The synthesized products have been characterized by structural (XRD, SEM), spectroscopic (FTIR, Raman) and thermal (DTA/TG) analyses. Raman and FTIR measurements provide information on the local environment of the cationic sublattice of LiNi0.6Co0.4O2 solid solution. Electrochemical performance of the synthesized products in rechargeable Li cells were evaluated by employing as cathodes in non-aqueous organic electrolyte mixture of 1M LiPF6 in EC + DMC. The electrochemical behaviour of synthesized LiNi0.6Co0.4O2 is discussed in relation with its synthesis procedure.
TL;DR: In this article, fresh-cut banana slices were treated with pineapple juice, neutral sugars, isoascorbic acid, citric acid, other organic acids, N-acetylcysteine, 4-hexylresor-cinol and mixtures of these compounds and evaluated for browning reaction.
Abstract: Fresh-cut banana slices were treated with pineapple juice, neutral sugars, isoascorbic acid, citric acid, other organic acids, N-acetylcysteine, 4-hexylresor-cinol and mixtures of these compounds and evaluated for browning reaction. A number of other compounds previously reported to be antibrowning agents were also tested. Preliminary tests revealed that many purported antibrowning agents, including pineapple juice, had only transitory or no effects on browning of banana slices. Subsequent replicated treatments of slices stored at 5C and 15C for 7 days showed that of the several treatments, those using citric acid and N-acetylcysteine were highly effective at reducing browning. Reflectance measurements taken immediately after treatment, after 2 days of storage, and at the end of the 1 week storage period confirmed that a mixture of 0.5 M citric acid and 0.05 M N-acetylcysteine provided the best protection against browning at both temperatures. No microbial decay was observed during the 7 day period studied.
TL;DR: Results show that an individual's cough response to acetic and phosphoric acid are similar to that caused by citric acid, which suggests these acids may cause cough by a common mechanism such as disturbance of the pH of the airway surface liquid.
TL;DR: The stability of the low-calorie sweetener stevioside during different processing and storage conditions, as well as the effects of its interaction with the water-soluble vitamins ascorbic acid, thiamin, riboflavin, pyridoxine and nicotinic acid were evaluated in this article.
Abstract: The stability of the low calorie sweetener stevioside during different processing and storage conditions, as well as the effects of its interaction with the water-soluble vitamins ascorbic acid, thiamin, riboflavin, pyridoxine and nicotinic acid, the organic acids acetic acid, citric acid, tartaric acid and phosphoric acid, the other common low calorie sweeteners saccharin, cyclamate, aspartame, acesulfame, neohesperidin dihydrochalcone, and caffeine in coffee and tea, were evaluated. Incubation of solid stevioside at elevated temperatures for 1 h showed good stability up to 120°C, whilst forced decomposition was noticed at temperatures exceeding 140°C. In aqueous solution stevioside was remarkably stable in a pH range of 2–10 under thermal treatment up to 80°C; however, under strong acidic conditions (pH 1), a significant decrease in the stevioside concentration was detected. Up to 4 h of incubation with individual water-soluble vitamins in aqueous solution at 80°C showed no significant changes with regard to stevioside and the B-vitamins, whereas a protective effect of stevioside on the degradation of ascorbic acid was observed, resulting in a significant delayed degradation rate. In the presence of other individual low calorie sweeteners, practically no interaction was found at room temperature after 4 months of incubation in aqueous media. Stability studies of stevioside in solutions of organic acids showed a tendency towards enhanced decomposition of the sweetener at lower pH values, depending on the acidic medium. In stevioside-sweetened coffee and tea, very few significant chances in caffeine content or in stevioside content were found.
TL;DR: Organic acids and their sodium salts, and nisin are preservatives commonly used in the type of foods from which the organism is recovered and their effect on the growth of A. butzleri in culture, alone and in combination was investigated.
Abstract: The importance of Arcobacter spp. as a cause of human foodborne illness is unresolved. Organic acids and their sodium salts, and nisin are preservatives commonly used in the type of foods from which the organism is recovered. In this study their effect on the growth of A. butzleri in culture, alone and in combination, was investigated. At 0.5%, 1.0% and 2.0% lactic and citric acids inhibited A. butzleri growth; 2% sodium lactate was effective in inhibiting growth over 8 h incubation but not over longer periods. Sodium citrate was more effective than sodium lactate. Nisin alone inhibited A. butzleri growth at 500 IU ml-1 over 5 h. It did not enhance the effect of sodium citrate inhibition but it did augment the effect of sodium lactate alone over 8 h.
Patent•
19 Oct 1999
TL;DR: In this article, the buffering agent allows a physiologically acceptable amount of citrate to maintain the desired pH of the dialysate, which is used for acid concentrates.
Abstract: Acid concentrates, and dialysate compositions prepared therefrom, contain citric acid and an effective amount of a buffering agent selected from acetate and/or lactate. The buffering agent allows a physiologically acceptable amount of citrate to maintain the desired pH of the dialysate.
TL;DR: It is suggested that application of glutathione in combination with citric acid may slow down the browning of litchi fruit.
Abstract: Polyphenol oxidase (PPO, EC 1.10.3.2) was purified to homogeneity from litchi peel yielding a single protein with a molecular weight of about 75.6 kD by Sephadex G-100 gel filtration, and a 108-fold purification of PPO achieved. The enzyme was determined to be composed of two similar subunits. Glutathione, L-cysteine and citric acid suppressed PPO activity markedly, whereas ascorbic acid and n-propyl gallate showed a little inhibition. Moreover, the effect was enhanced by the addition of citric acid. On the basis of the inhibition of PPO activity in vitro, the use of 10 mmol l −1 glutathione and 100 mmol−1 l citric acid was found to give good control of the browning of litchi fruit, and an 80–85% inhibition of PPO activity was observed. It is suggested that application of glutathione in combination with citric acid may slow down the browning of litchi fruit. © 1999 Society of Chemical Industry
TL;DR: In this article, the authors investigate cotton fabric yellowing caused by citric acid at elevated temperatures and find that yellowing increases as curing temperature, curing time, and CA concentration increase.
Abstract: Citric acid (CA), one of the polycarboxylic acids used as crosslinking agents for cotton, is cost-effective and environmentally friendly, but its tendency to discolor fabric is a major disadvantage for white fabrics. In this research, we investigate cotton fabric yellowing caused by citric acid at elevated temperatures. We find that yellowing increases as curing temperature, curing time, and CA concentration increase. Using sodium hypophosphite as a catalyst causes less fabric yellowing than monosodium phosphate. The wet analysis data demonstrate that an alkene double bond is formed on cotton fabric treated with CA under curing conditions. Nuclear magnetic resonance (NMR) data indicate that CA is partially converted to trans- and cis-aconitic acids on cotton through dehydration. The visible spectra of fabric treated with trans- and cis-aconitic acids and cured at elevated temper atures show strong absorption in the 400-550 nm region. For polymeric multifunctional carboxylic acids, an increased number of h...