Showing papers on "Acetic acid published in 2002"
TL;DR: The selective production of organic acids by anaerobic acidogenesis with pH control was examined using a chemostat culture, and the results showed that the product spectrum in the acid reactor strongly depended on the culture pH.
345 citations
TL;DR: The mechanism by which methionine relieves the growth inhibition of Escherichia coli K-12 that is caused by organic weak acid food preservatives was investigated and it was revealed that the homocysteine pool is increased dramatically in acetate-treated cells, suggesting that acetate inhibits a biosynthetic step downstream from this intermediate.
Abstract: The mechanism by which methionine relieves the growth inhibition of Escherichia coli K-12 that is caused by organic weak acid food preservatives was investigated. In the presence of 8 mM acetate the specific growth rate of E. coli Frag1 (in MacIlvaine's minimal medium pH 6.0) is reduced by 50%. Addition of methionine restores growth to 80% of that observed in untreated controls. Similar relief was seen with cultures treated with either benzoate or propionate. Mutants with an elevated intracellular methionine pool were almost completely resistant to the inhibitory effects of acetate, suggesting that the methionine pool becomes limiting for growth in acetate-treated cells. Measurement of the intracellular concentrations of pathway intermediates revealed that the homocysteine pool is increased dramatically in acetate-treated cells, suggesting that acetate inhibits a biosynthetic step downstream from this intermediate. Supplementation of the medium with homocysteine inhibits the growth of E. coli cells. Acetate inhibition of growth arises from the depletion of the intracellular methionine pool with the concomitant accumulation of the toxic intermediate homocysteine and this augments the effect of lowering cytoplasmic pH.
318 citations
TL;DR: In this paper, chitosan films were prepared using 3 chitoshan molecular weights and 4 organic acid solvents without plasticizer, and the results showed that tensile strength and elongation increased with the molecular weight.
Abstract: Chitosan films were prepared using 3 chitosan molecular weights and 4 organic acid solvents without plasticizer. Tensile strength (TS) and elongation (E) ranged from 6.7 to 150.2 MPa, and from 4.1 to 117.8%, respectively. Water vapor permeability (WVP) and oxygen permeability (OP) ranged from 0.3 to 0.7 ng-m/m2-s-Pa and OP from 0.4 to 5.8 × 10 −8 cc/m2-day-atm, respectively. TS increased with chitosan molecular weight. Acetic acid resulted in the toughest films followed by malic, lactic, and citric acid, respectively. Films prepared with citric acid had the highest E values. WVP was not influenced significantly by the molecular weight of chitosan. OP of films prepared with malic acid was the lowest, followed by acetic, lactic, and citric acid.
317 citations
TL;DR: In this paper, a reaction pathway of phenol oxidation under intermediate temperature and pressure has been proposed, where the main intermediates detected in the phenol oxidization were ring compounds (hydroquinone, catechol, benzoquinone), which break to yield CO 2 and short chain acids, mainly maleic, formic, acetic and oxalic acids, and also traces of malonic, succinic and fumaric acids.
Abstract: Catalytic oxidation of phenol in aqueous phase over a copper catalyst supplied by Engelhard (Cu-0203T) has been studied. A reaction pathway of phenol oxidation under intermediate temperature and pressure has been proposed. Temperatures employed were 140 and 160 °C and catalyst concentration ranged from 4 to 1550 g l −1 of liquid phase. To achieve this wide interval of catalyst concentration values, two experimental set-ups were employed: a basket stirred tank reactor (BSTR), with the liquid phase in batch, and an integral fixed-bed reactor (FBR) with co-current up-flow of gas and liquid phases. The main intermediates detected in the phenol oxidation were ring compounds (hydroquinone, catechol, benzoquinone), which break to yield CO 2 and short chain acids, mainly maleic, formic, acetic and oxalic acids, and also traces of malonic, succinic and fumaric acids. Oxalic acid was also found to form a complex with the copper which oxidizes to CO 2 . The only non-oxidizable intermediate under the conditions sets was acetic acid. In order to propose a phenol oxidation pathway, several runs were carried out where the main intermediates detected in the phenol oxidation were fed to the FBR under different temperatures and catalyst loadings. It was found that catechol oxidation does not yield either benzoquinone or maleic acid but oxalic acid which finally mineralized to CO 2 . However, benzoquinone and maleic acid are products clearly detected in the hydroquinone oxidation. Oxidation reactions of phenol and those intermediates studied take place not only on the solid surface but also in the liquid phase.
273 citations
01 May 2002
258 citations
TL;DR: Partial least-squares regression models confirm that amino acid composition explains a high proportion of the variance in the volatile composition and show that the relationship between both sets of variables is highly multivariate.
Abstract: Synthetic solutions containing amino acids, sugar, water, and yeast nutrients have been fermented by Saccharomyces cerevisiae, and the volatile composition of the fermented media has been analyzed by GC. Eleven amino acid compositions imitating the characteristic amino acid profile of 11 different grape varieties were tested. Significant differences in the levels of some important volatile compounds (ethanol, ethyl acetate, acetic acid, higher alcohols and some of their acetates, methionol, isobutyric acid, ethyl butyrate, and hexanoic and octanoic acids) were found. The levels of some of the volatile compounds are well correlated with the aromatic composition of wines made with grapes of the same varieties. A multiple linear regression study produced good models for most of the odorants for which the level was related to the must amino acid composition. Partial least-squares regression models confirm that amino acid composition explains a high proportion of the variance in the volatile composition and sh...
241 citations
TL;DR: In this paper, nonlocal density functional theory (DFT) calculations are used to examine alternative mechanisms for the hydrogenolysis of acetic acid to ethanol over Pd, and the overall surface reaction energies, at low surface coverage, are computed for a number of different possible paths by which the acid may be converted to ethanol, and binding energies of various oxygenated C 2 intermediates formed along these paths are also reported.
241 citations
TL;DR: 1,3,5-Trisubstituted pyrazolines and Hantzsch 1,4-dihydropyridine were converted to the corresponding pyrazoles and pyridines effectively by the treatment of a catalytic amount of Pd/C in acetic acid.
222 citations
TL;DR: The results indicated that the buffer pair formed when the pH was adjusted to 4.5 stabilized the pH of the medium by sequestering protons and by lessening the negative impact of the pH drop on yeast growth, and it also decreased the difference between the extracellular and intracellular pH values (ΔpH), the driving force for the intrACEllular accumulation of acid.
Abstract: Acetic acid (167 mM) and lactic acid (548 mM) completely inhibited growth of Saccharomyces cerevisiae both in minimal medium and in media which contained supplements, such as yeast extract, corn steep powder, or a mixture of amino acids. However, the yeast grew when the pH of the medium containing acetic acid or lactic acid was adjusted to 4.5, even though the medium still contained the undissociated form of either acid at a concentration of 102 mM. The results indicated that the buffer pair formed when the pH was adjusted to 4.5 stabilized the pH of the medium by sequestering protons and by lessening the negative impact of the pH drop on yeast growth, and it also decreased the difference between the extracellular and intracellular pH values (ΔpH), the driving force for the intracellular accumulation of acid. Increasing the undissociated acetic acid concentration at pH 4.5 to 163 mM by raising the concentration of the total acid to 267 mM did not increase inhibition. It is suggested that this may be the direct result of decreased acidification of the cytosol because of the intracellular buffering by the buffer pair formed from the acid already accumulated. At a concentration of 102 mM undissociated acetic acid, the yeast grew to higher cell density at pH 3.0 than at pH 4.5, suggesting that it is the total concentration of acetic acid (104 mM at pH 3.0 and 167 mM at pH 4.5) that determines the extent of growth inhibition, not the concentration of undissociated acid alone.
185 citations
TL;DR: There was amide formation between chitosan and organic acids after treatment especially in chitOSan acetate and propionate films, and change in the degree of crystallinity from powder X-ray diffractogram and thermal characteristic from DSC thermogram were related to the water sorption and dissolution of films.
176 citations
TL;DR: The FBB technology is suitable for producing value-added biochemicals directly from agricultural residues or commodities such as corn meal, suggesting that these carboxylic acids can be efficiently produced from direct fermentation of corn meal hydrolyzate.
TL;DR: In this article, 2,3-Dihydro-1H-1,5-benzodiazepines have been synthesized in solvent-free conditions from o-phenylenediamines and ketones in the presence of a catalytic amount of acetic acid, under microwave irradiation.
TL;DR: Analysis of the metabolome of the mutants revealed that genetic modification affected the production of some secondary metabolites of fermentation, including acids, esters, aldehydes and higher alcohols, many of which are flavour‐active in wine.
Abstract: Glycerol is a major fermentation product of Saccharomyces cerevisiae that contributes to the sensory character of wine. Diverting sugar to glycerol overproduction and away from ethanol production by overexpressing the glycerol 3-phosphate dehydrogenase gene,GPD2, caused S. cerevisiae to produce more than twice as much acetic acid as the wild-type strain (S288C background) in anaerobic cell culture. Deletion of the aldehyde dehydrogenase gene, ALD6, in wild-type and GPD2 overexpressing strains (GPD2-OP) decreased acetic acid production by three- and four-fold, respectively. In conjunction with reduced acetic acid production, the GPD2-OP ald6Δ strain produced more glycerol and less ethanol than the wild-type. The growth rate and fermentation rate were similar for the modified and wild-type strains, although the fermentation rate for the GPD2ald6Δ strain was slightly less than that of the other strains from 24 h onwards. Analysis of the metabolome of the mutants revealed that genetic modification affected the production of some secondary metabolites of fermentation, including acids, esters, aldehydes and higher alcohols, many of which are flavour-active in wine. Modification of GPD2 and ALD6 expression represents an effective strategy to increase the glycerol and decrease the ethanol concentration during fermentation, and alters the chemical composition of the medium such that, potentially, novel flavour diversity is possible. The implications for the use of these modifications in commercial wine production require further investigation in wine yeast strains. Copyright © 2002 John Wiley & Sons, Ltd.
TL;DR: The series of identified metabolites suggests that anaerobic degradation of naphthalenes proceeds via reduction of the aromatic ring system of 2-naphthoic acid to initiate ring cleavage in analogy to the benzoyl-coenzyme A pathway for monoaromatic hydrocarbons.
Abstract: Anaerobic degradation of naphthalene, 2-methylnaphthalene, and tetralin (1,2,3,4-tetrahydronaphthalene) was investigated with a sulfate-reducing enrichment culture obtained from a contaminated aquifer. Degradation studies with tetralin revealed 5,6,7,8-tetrahydro-2-naphthoic acid as a major metabolite indicating activation by addition of a C1 unit to tetralin, comparable to the formation of 2-naphthoic acid in anaerobic naphthalene degradation. The activation reaction was specific for the aromatic ring of tetralin; 1,2,3,4-tetrahydro-2-naphthoic acid was not detected. The reduced 2-naphthoic acid derivatives tetrahydro-, octahydro-, and decahydro-2-naphthoic acid were identified consistently in supernatants of cultures grown with either naphthalene, 2-methylnaphthalene, or tetralin. In addition, two common ring cleavage products were identified. Gas chromatography-mass spectrometry (GC-MS) and high-resolution GC-MS analyses revealed a compound with a cyclohexane ring and two carboxylic acid side chains as one of the first ring cleavage products. The elemental composition was C11H16O4 (C11H16O4-diacid), indicating that all carbon atoms of the precursor 2-naphthoic acid structure were preserved in this ring cleavage product. According to the mass spectrum, the side chains could be either an acetic acid and a propenic acid, or a carboxy group and a butenic acid side chain. A further ring cleavage product was identified as 2-carboxycyclohexylacetic acid and was assumed to be formed by β-oxidation of one of the side chains of the C11H16O4-diacid. Stable isotope-labeling growth experiments with either 13C-labeled naphthalene, per-deuterated naphthalene-d8, or a 13C-bicarbonate-buffered medium showed that the ring cleavage products derived from the introduced carbon source naphthalene. The series of identified metabolites suggests that anaerobic degradation of naphthalenes proceeds via reduction of the aromatic ring system of 2-naphthoic acid to initiate ring cleavage in analogy to the benzoyl-coenzyme A pathway for monoaromatic hydrocarbons. Our findings provide strong indications that further degradation goes through saturated compounds with a cyclohexane ring structure and not through monoaromatic compounds. A metabolic pathway for anaerobic degradation of bicyclic aromatic hydrocarbons with 2-naphthoic acid as the central intermediate is proposed.
TL;DR: In this article, a mesoporous MCM-41 molecular sieves with acetic acid as solvent, hydrogen peroxide as oxidant, and methyl ethyl ketone as initiator was used for liquid phase oxidation of cyclohexane.
TL;DR: In this paper, the authors used Mossbauer spectroscopy to characterize a family of supported Pt-Fe catalysts and found that the addition of small amounts of Pt to Fe/SiO 2 catalysts increased Fe reducibility during the reduction pretreatment, increased activity more than 10-fold and turnover frequencies 10- to 100-fold, eliminated the induction period, and still maintained a high selectivity to acetaldehyde.
TL;DR: In this article, the authors present and discuss a number of aliphatic polyesters which show interesting applications as biomedical materials and degradable packages, starting with succinic acid and/or 1,3-propanediol.
Abstract: From the point of view of making novel polymers with inherent environment-favorable properties such as renewability and degradability, a series of interesting monomers are found in the metabolisms and cycles of nature. This review presents and discusses a number of aliphatic polyesters which show interesting applications as biomedical materials and degradable packages. Available from nature are amino acids, microbial metabolites from the conversion of glucose and other monosaccharides (e.g., acetic acid, acetone, 2,3-butanediol, butyric acid, isopropanol, propionic acid), lactic acid, ethanol and fatty acids. A series of biodegradable polymers with different properties and different potential industrial uses were made starting with succinic acid and/or 1,3-propanediol. There were two routes for making the polyester-based materials; the direct ring-opening polymerization of lactones (cyclic esters) synthesized from 1,3-propanediol, and the chain-extension of α,ω-dihydroxy-terminated oligomeric polyesters produced by thermal polycondensation of 1,3-propanediol and succinic acid (oligo(propylene succinate)s).
TL;DR: Production of low-molecular-weight carboxylic acids from the hydrothermal treatment of representative organic wastes and compounds with or without oxidant demonstrated that the presence of oxidants favored formation of organic acids with acetic acid being the major product.
TL;DR: A recently discovered clostridial bacteria converts components of synthesis gas (CO, CO 2, H 2 ) into liquid products such as ethanol, butanol, and acetic acid as discussed by the authors.
Abstract: A recently discovered clostridial bacteria converts components of synthesis gas (CO, CO 2 , H 2 ) into liquid products such as ethanol, butanol and acetic acid Isolated from an agricultural lagoon, the stability and productivity characteristics of the bacteria were studied in a continuous 45 l bubble column bioreactor at 37°C using artificial blends of CO, CO 2 , and N 2 Preliminary results on the rates of cell growth, substrate utilization, product formation, and yields of products and cells from CO are discussed At steady state, apparent yields (mole C in products per mole CO consumed) of ethanol, butanol, and acetic acid were 015, 0075 and 0025, respectively, and the cell yield was 025 g / mol CO The theoretical yield of ethanol is 033 if CO is only utilized for the production of ethanol The experimental yield of CO 2 from CO was approximately 60% compared to the theoretical yield of 67% with ethanol as the sole product As a comparison with another ethanol-producing bacteria, the results of a similar fermentation study using batch-grown Clostridium ljungdahlii showed yields of 0062 for ethanol and 0094 for acetic acid and a cell yield of 1378 g / mol
TL;DR: Isoamyl acetate production is possible at a high acetic acid concentration (3.6 M) using Novozym 435 in a solvent-free system using immobilized Rhizomucor miehei and Candida antarctica lipases and is higher than those reported by other researchers.
TL;DR: In this paper, the development of a heterogeneously catalyzed reactive distillation process for the production of n-butyl acetate by esterification of nbutanol with acetic acid is presented.
Abstract: The development of a heterogeneously catalyzed reactive distillation process for the production of n-butyl acetate by the esterification of n-butanol with acetic acid is presented. Thermodynamic aspects of the considered system are discussed, and UNIQUAC interaction parameters are given. The reaction was catalyzed heterogeneously by a strongly acidic ion-exchange resin (Amberlyst-15). The reaction kinetics was investigated, and the kinetic constants for a pseudohomogeneous kinetic model are presented. Reactive distillation experiments were performed using the structured catalytic packing Katapak-S. Several operation conditions were varied (reboiler duty, reactant ratio, total feed rate), and two different setups were realized experimentally. The experimental results are presented in comparison with simulation results. An equilibrium stage model is capable of describing the experiments quantitatively. n-Butanol conversions of 98.5% accompanied with n-butyl acetate purities of 96.9% were achieved using an e...
TL;DR: In this article, a reaction mechanism was modified slightly to incorporate an acyl species as the principal intermediate, rather than molecular acetic acid, and the resulting rate expression not only gives an identical fit to the kinetic data, but also possesses thermodynamically meaningful parameters, such as the heat of adsorption of H 2 on Pt, that are consistent with literature values.
TL;DR: This study showed that A. liquefaciens and A. hansenii were present in significant numbers, which has not been reported before, in South African red wine fermentations.
TL;DR: In this article, the principle decomposition products were acetone (about 2 mole per mole TATP in the gas-phase and 2.5 ± 2.13 s 1.
Abstract: 13 s 1 . Under all conditions the principle decomposition products were acetone (about 2 mole per mole TATP in the gas-phase and 2.5 ± 2.6 mole per mole in condensed-phase) and carbon dioxide. Minor products included some ascribed to reactions of methyl radical: ethane, methanol, 2-butanone, ethyl acetate; these increased at high temperature. Methyl acetate and acetic acid were also formed in the decomposition of neat TATP; the former was more evident in the gasphase decompositions (151C and 230C) and the latter in the condensed-phase decompositions (151C). The decomposition of TATP in condensed-phase or in hydrogen-donating solvents enhanced acetone production, suppressed CO2 production, and slightly increased the rate constant (a factor of 2 ± 3). All observations were interpreted in terms of decomposition pathways initiated by OO homolysis.
TL;DR: The results obtained from the chromatograms suggest that some compounds present in the extract possess high radical quenching ability.
TL;DR: Sildenafil and its metabolite UK‐103,320 in human serum were detected by solid‐phase extraction followed by capillary zone electrophoresis‐mass spectrometry analysis and showed good intraday precision in terms of relative standard deviation (RSD).
Abstract: Ionic liquid (IL) was covalently bonded onto the silica capillary surface and the electroosmotic flow was reversed over a pH range of 3.5 to 7. Sildenafil (SL) and its metabolite UK-103,320 (UK) in human serum were detected by solid-phase extraction followed by capillary zone electrophoresis-mass spectrometry analysis. The running buffer contained 10 mM acetic acid adjusted to pH 4.5 with 1 M ammonia, and the separating voltage was set to -25 kV. The adsorption of the analytes onto the bare capillary wall was eliminated by the IL coating and the drugs were baseline-separated within 14 min with detection limits (S/N = 3) of 14 and 17 ng/mL for SL and UK, respectively. The method developed showed good intraday precision in terms of relative standard deviation (RSD) with respect to migration time (RSD
TL;DR: It is demonstrated that xylose fermentation to ethanol can be improved in KO11 by redirecting small amounts of pyruvate away from fermentation products and into biosynthesis.
Abstract: The production of ethanol from xylose by ethanologenic Escherichia coli strain KO11 was improved by adding various medium supplements (acetate, pyruvate, and acetaldehyde) that prolonged the growth phase by increasing cell yield and volumetric productivity (approximately twofold). Although added pyruvate and acetaldehyde were rapidly metabolized, the benefit of these additives continued throughout fermentation. Both additives increased the levels of extracellular acetate through different mechanisms. Since acetate can be reversibly converted to acetyl coenzyme A (acetyl-CoA) by acetate kinase and phosphotransacetylase, the increase in cell yield caused by each of the three supplements is proposed to result from an increase in the pool of acetyl-CoA. A similar benefit was obtained by inactivation of acetate kinase (ackA), reducing the production of acetate (and ATP) and sparing acetyl-CoA for biosynthetic needs. Inactivation of native E. coli alcohol-aldehyde dehydrogenase (adhE), which uses acetyl-CoA as an electron acceptor, had no beneficial effect on growth, which was consistent with a minor role for this enzyme during ethanol production. Growth of KO11 on xylose appears to be limited by the partitioning of carbon skeletons into biosynthesis rather than the level of ATP. Changes in acetyl-CoA production and consumption provide a useful approach to modulate carbon partitioning. Together, these results demonstrate that xylose fermentation to ethanol can be improved in KO11 by redirecting small amounts of pyruvate away from fermentation products and into biosynthesis. Though negligible with respect to ethanol yield, these small changes in carbon partitioning reduced the time required to complete the fermentation of 9.1% xylose in 1% corn steep liquor medium from over 96 h to less than 72 h.
TL;DR: The fate of the Amadori compound N-(1-deoxy-D-fructos-1-yl)glycine (DFG) was studied in aqueous model systems as a function of time and pH, with special attention paid to the effect of phosphate on the formation of glycine and the parent sugars glucose and mannose, as well as formic and acetic acid.
Abstract: The fate of the Amadori compound N-(1-deoxy-D-fructos-1-yl)glycine (DFG) was studied in aqueous model systems as a function of time and pH. The samples were reacted at 90 degrees C for up to 7 h while maintaining the pH constant at 5, 6, 7, or 8. Special attention was paid to the effect of phosphate on the formation of glycine and the parent sugars glucose and mannose, as well as formic and acetic acid. These compounds and DFG were quantified by high-performance anion-exchange chromatography. The rate of DFG degradation increased with pH. Addition of phosphate accelerated this reaction, particularly at pH 5-7. The rate of glycine formation increased with pH in both the absence and presence of phosphate. High glycine concentrations (60-70 mol %) were obtained, preferably at pH 6-8 with phosphate. However, the yield of glycine formed from DFG decreased at the advanced reaction stage for all pH values studied, both in water and in phosphate buffer. The rate of parent sugar formation increased from pH 5 to pH 7 in the absence of phosphate, leading to glucose and mannose in a constant ratio of 7:3. Addition of phosphate accelerated this reaction, yielding up to 18% parent sugars, most likely formed by reverse Amadori rearrangement. The formation rate of acetic and formic acid increased with increasing pH. The sum of both acids attained 76 mol %. However, the acetic acid concentrations were much higher than those of formic acid.
TL;DR: In this article, a high-performance liquid chromatography (HPLC) system with a C18 column and an aqueous phase eluent (0.08% ammonium acetate and 0.02% L-cysteine) was used to study the abiotic formation of methylmercury, CH3Hg+, from inorganic mercury, Hg2+, as well as demethylation of CH 3Hg+ to Hg 2+ in biological tissues during treatment with tetramethylammonium hydroxide (TMAH) followed
Abstract: A high-performance liquid chromatography (HPLC) system with a C18 column and an aqueous phase eluent (0.08% ammonium acetate and 0.02%
L-cysteine) was directly connected to an inductively coupled plasma mass spectrometer (ICP-MS). HPLC-ICP-MS was used to study the abiotic formation of methylmercury, CH3Hg+, from inorganic mercury, Hg2+, as well as demethylation of CH3Hg+ to Hg2+ in biological tissues during treatment with tetramethylammonium hydroxide (TMAH) followed by pH adjustment with citric or acetic acid. Enriched isotope standards from CH3198Hg+ and 201Hg2+ were added to the samples to monitor species transformation and to apply species-specific isotope dilution (SSID) calibration. Depending on the type of sample matrix, up to 11.5% of added Hg2+ was methylated and up to 6.26% CH3Hg+ was demethylated to Hg2+. Methylation of Hg2+ probably takes place mainly during and after pH adjustment and it decreases after prolonged TMAH treatment. To minimize abiotic methylation, it is therefore recommended to proceed with pH adjustment after samples have been treated with TMAH for 24 h. There is no significant difference in the degree of methylation using citric or acetic acid.
TL;DR: Determination of acid composition revealed lactic acid production for active dairy strains and the presence of acetic acid in active as well as inactive strains, and it was demonstrated that the undissociated acetic Acid originates from the bacterial growth medium.