Showing papers on "Acetic acid published in 1991"

Inhibiting factors produced by lactic acid bacteria. 1. Oxygen metabolites and catabolism end-products

Abstract: Summary - Lactic acid bacteria can produce a variety of antimicrobial compounds which may affect both the lactic acid bacteria themselves as weil as undesirable or pathogenic strains. In this first section, we describe the biosynthesis, mode of action and activity spectra of these inhibitors. Metabolites of oxygen (hydrogen peroxide and free radicals) exhibit a bacteriostatic or bactericidal activity against lactic or non-Iactic flora. When associated with the lactoperoxidase/thiocyanate system, hydrogen peroxide leads to the formation of inhibitory compounds which are bacteriostatic for lactic acid bacteria and bactericidal for Gram-negative bacteria. The antimicrobial activity of organic acids (Iactic, acetic and formic) and of pH are closely linked. It appears that the non-dissociated fraction of these acids is the major inhibitory form. Thus, acetic acid whose pKa is higher than that of lactic acid exhibits the highest inhibitory activity. The antimicrobial activities of diacetyl, acetaldehyde and of the D isomers of amino acids are also described, although their effects are slight in usual lactic fermentations. 8acteriocins are the last type of inhibitory substance produced by some lactie acid bacteria. They will be described in a second section. lactic acid bacteria / oxygen 1acidity 1diacetyll acetaldehyde

Glycerol fermentation of 1,3-propanediol by Clostridium butyricum . Measurement of product inhibition by use of a pH-auxostat

Abstract: The fermentation of glycerol to 1,3-propanediol, acetate, and butyrate by Clostridium butyricum was studied with respect to growth inhibition by the accumulating products. The clostridia were grown in a pH-auxostat culture at low cell density and product concentration and near maximum growth rate. The products were then added individually to the medium in increasing concentrations and the resulting depression of growth rate was used as a quantitative estimate of product inhibition. Under these conditions growth was totally inhibited at concentrations of 60 g/l for 1,3-propanediol, 27 g/l for acetic acid and 19 g/l for butyric acid at pH 6.5. Appreciable inhibition by glycerol was found only above a concentration of 80 g/l. In a pH-auxostat without added products but with high cell density as well as in batch cultures the product proportions were different. The 1,3-propanediol concentration may approach the value of complete inhibition while the concentrations of acetic and butyric acids remained below these values by at least one order of magnitude. It was therefore concluded that 1,3-propanediol is the first range inhibitor in this fermentation.

Facilitated isolation, purification, and analysis of glucuronoxylomannan of Cryptococcus neoformans.

Abstract: Cryptococcus neoformans was cultured in a chemically defined medium. The culture was adjusted to 0.25% formaldehyde or autoclaved after 5 days of growth at 35 degrees C, and a cell-free supernatant was obtained by centrifugation. Solid calcium acetate was added to the supernatant to give a 5% solution, and the pH was adjusted to approximately 5 with glacial acetic acid. The polysaccharide (PS) was precipitated by the addition of 3 volumes of 95% ethanol. The PS was dissolved in 0.2 M NaCl, and insoluble calcium salts were solubilized by the addition of several drops of glacial acetic acid. The PS solution was treated by ultrasonic irradiation for 15 min. This concurrently decreased the molecular weight of the PS and reduced the viscosity of the solution. The ultrasonically irradiated PS was precipitated by differential complexation with hexadecyltrimethylammonium bromide at 23 degrees C, the complex was dissolved in 1 M NaCl, and the glucuronoxylomannan was precipitated by adding 3 volumes of ethanol. The glucuronoxylomannan was dissolved in 1 M NaCl and then ultrasonically irradiated for 2 h to reduce the molecular mass to a limiting value of approximately 100 kDa (GXMS). The purified GXMS was centrifuged, dialyzed, and finally recovered by lyophilization. GXMS was chromatographed on DEAE-cellulose at reasonable concentrations without the complication of high solution viscosity. The sugar composition and structure of GXMS were determined by gas-liquid chromatography, permethylation gas-liquid chromatography-mass spectrometry, and 13C nuclear magnetic resonance spectroscopy. The improved solution characteristics of GXMS were ideal for the determination of its chemical and serological properties.

Propionic acid fermentation of lactose by Propionibacterium acidipropionici: effects of pH.

Abstract: Batch propionic acid fermentation of lactose by Propionibacterium acidipropionici were studied at various pH values ranging from 4.5 to 7.12. The optimum pH range for cell growth was between 6.0 and 7.1, where the specific growth rate was approximately 0.23 h(-1). The specific growth rate decreased with the pH in the acids have been identified as the two major fermentation products from lactose. The production of propionic acid was both growth and nongrowth associated, while acetic acid formation was closely associated with cell growth. The propionic acid yield increased with decreasing pH; It changed from approximately 33% (w/w) at pH 6.1-7.1 to approximately 63% at pH 4.5-5.0. In contrast, the acetic acid yield was not significantly affected by the pH; it remained within the range of 9%-12% at all pH values. Significant amounts of succinic and pyruvic acids were also formed during propionic acid fermentation of lactose. However, pyruvic acid was reconsumed and disappeared toward the end of the fermentation. The succinic acid yield generally decreased with the pH, from a high value of 17% at pH 7.0 to a low 8% at pH 5.0 Effects of growth nutrients present in yeast ex-tract on the fermentation were also studied. In general, the same trend of pH effects was found for fermentations with media containing 5 to 10 g/L yeast extract. However, More growth nutrients would be required for fermentations to be carried out efficienytly at acidic pH levels.

Hydrothermal preparation of barium titanate from barium-titanium acetate gel precursors

Abstract: Clear, transparent gels of BaTi acetate have been prepared from titanium tetrabutylate (TBT), Ba acetate aqueous solution, isopropanol and acetic acid. Infrared spectroscopy and transmission electron microscopy (TEM) of such gels revealed linked clusters of polymer Ti oxyacetate with surface adsorbed Ba acetate. Spray dried Ti oxyacetate has been found to have the stoichiometric composition Ti 2 O 3 [CH 3 COO] 2 . Calcination of BaTi acetate gels to BaTiO 3 in air turned out to be a less favourable preparative route, because stable intermediate carbonate phases were formed. Corresponding to the high surface area and fine dispersion of Ba and Ti, BaTi acetate gels are higly reactive precursors for hydrothermal synthesis of BaTiO 3 . Nearly quantitative (> 99·7%) chemical reactions were obtained without using Ba excess at processing. TEM provided interesting information about the chemical mechanisms of hydrothermal processing.

Central nervous system effects of acetate: contribution to the central effects of ethanol.

Abstract: Acetate, resulting from ethanol metabolism in the liver, is released into the circulation and is utilized in a number of tissues, including the brain. In its metabolism, acetate leads to the production of adenosine, a powerful physiological mediator. We have investigated the effect of acetate on central nervous system (CNS) function in rodents. Sodium acetate in doses resulting in blood concentrations comparable to those attained after the administration of 1 to 2 g/kg ethanol, had significant CNS effects. Both ethanol and acetate produced a dose-dependent impairment of motor coordination. This effect of acetate was fully blocked by the adenosine receptor blocker 8-phenyltheophylline (8PT), whereas the dose-response relationship for ethanol was shifted to the right by about 30%. The inspired concentration of sevoflurane to achieve anesthesia was significantly reduced by both these agents. General anesthesia was potentiated in a dose-dependent fashion by ethanol and by acetate. The effect of acetate on anesthetic requirements was fully blocked by 8PT. The effect of ethanol on sevoflurane anesthetic requirements was inhibited by 22 to 35% by 8PT. Locomotor activity in mice was reduced by acetate in a dose-dependent fashion, an effect that was also fully blocked by 8PT. On the other hand, ethanol at a dose of 1 to 2 g/kg increased locomotor activity. This likely results from a direct stimulatory effect of ethanol, opposed by an inhibitor effect of acetate. The administration of 8PT enhanced the stimulation of locomotor activity induced by ethanol. In conclusion, acetate, a product of ethanol metabolism has significant CNS effects that can either potentiate or antagonize the effects of the ethanol molecule per se.(ABSTRACT TRUNCATED AT 250 WORDS)

Reforming of ethanol-dehydrogenation to ethyl acetate and steam reforming to acetic acid over copper-based catalysts

Abstract: The title reactions, 2CH3CH2OH→CH3COOC2H5+2H2 and CH3CH2OH+H2O→CH3COOH+2H2, were carried out over copper-based catalysts (Cu, Cu/SiO2, Cu/ZrO2, Cu/Al2O3, Cu/MgO, and Cu/ZnO). The selectivities to ethyl acetate and acetic acid markedly depended upon the supports used. Acetaldehyde was formed by the dehydrogenation of ethanol and transformed to either ethyl acetate or acetic acid through steps in which a nucleophilic addition of ethanol (or ethoxide ions) or water (or hydroxide ions) to acetaldehyde occurred. The rates of the transformation steps to ethyl acetate and acetic acid were appreciably affected by the kinds of supports used. The transformation steps proceeded slowly, compared with the dehydrogenation step.

Propionic Acid Production by a Propionic Acid-Tolerant Strain of Propionibacterium acidipropionici in Batch and Semicontinuous Fermentation.

Abstract: A propionic acid-tolerant derivative of Propionibacterium acidipropionici P9 was obtained by serially transferring strain P9 through broth that contained increasing amounts of propionic acid After 1 year of repeated transfers, a strain (designed P200910) capable of growth at higher propionic acid concentrations than P9 was obtained An increase in the proportion of cellular straight-chain fatty acids and uncoupling of propionic acid production from growth were observed for strain P200910 Growth rate, sugar utilization, and acid production were monitored during batch and semicontinuous fermentations of semidefined medium and during batch fermentation of whey permeate for both strain P200910 and strain P9 The highest propionic acid concentration (47 g/liter) was produced by P200910 in a semicontinuous fermentation Strain P200910 produced a higher ratio of propionic acid to acetic acid, utilized sugar more efficiently, and produced more propionic acid per gram of biomass than did its parent in all fermentations

Microbial flocculant from Alcaligenes cupidus KT201

Abstract: A microbial-flocculant-producing Gram-negative bacterium, strain KT201, was isolated from soil samples and identified as Alcaligenes cupidus. This strain secreted flocculant in a culture broth having a flocculant production medium which included sucrose. The flocculant (Al-201) was found to aggregate a suspended kaolin solution without cations, although its flocculating ability was significantly enhanced by the addition of bivalent/trivalent cations such as Ca2 + and Al3 +. Al-201 was purified by precipitation with ethanol and cetylpyridinium chloride, and had a gel filtration chromatography molecular weight of over 2 × 106. The constituent sugars of Al-201 were glucose, galactose, and glucuronic acid (molar ratio, 6.34: 5.55:1.0), with this flocculant occurring in 10.3% acetic acid as an acetyl ester group.

Resistance of Streptococcus bovis to acetic acid at low pH: relationship between intracellular pH and anion accumulation.

Abstract: Streptococcus bovis JB1, an acid-tolerant ruminal bacterium, was able to grow at pHs from 6.7 to 4.5, and 100 mM acetate had little effect on growth rate or proton motive force across the cell membrane. When S. bovis was grown in glucose-limited chemostats at pH 5.2, the addition of sodium acetate (as much as 100 mM) had little effect on the production of bacterial protein. At higher concentrations of sodium acetate (100 to 360 mM), production of bacterial protein declined, but this decrease could largely be explained by a shift in fermentation products (acetate, formate, and ethanol production to lactate production) and a decline in ATP production (3 ATP per glucose versus 2 ATP per glucose). YATP (grams of cells per mole of ATP) was not decreased significantly even by high concentrations of acetate. Cultures supplemented with 100 mM sodium acetate took up [14C]acetate and [14C]benzoate in accordance with the Henderson-Hasselbalch equation and gave similar estimates of intracellular pH. As the extracellular pH declined, S. bovis allowed its intracellular pH to decrease and maintained a relatively constant pH gradient across the cell membrane (0.9 unit). The decrease in intracellular pH prevented S. bovis from accumulating large amounts of acetate anion. On the basis of these results it did not appear that acetate was acting as an uncoupler. The sensitivity of other bacteria to volatile fatty acids at low pH is explained most easily by a high transmembrane pH gradient and anion accumulation.

Transport of monocarboxylic acids at the blood-brain barrier: studies with monolayers of primary cultured bovine brain capillary endothelial cells.

Abstract: The kinetics and mechanism of the transport of monocarboxylic acids (MCAs) were studied by using primary cultured bovine brain capillary endothelial cells. Concentration-dependent uptake of acetic acid was observed, and the kinetic parameters were estimated as follows: the Michaelis constant, Kt, was 3.41 +/- 1.87 mM, the maximum uptake rate, Jmax, was 144.7 +/- 55.7 nmol/mg of protein/min and the nonsaturable first-order rate constant, Kd, was 6.66 +/- 1.98 microliters/mg of protein/min. At medium pH below 7.0, the uptake rate of [3H]acetic acid increased markedly with decreasing medium pH, whereas pH-independent uptake was observed in the presence of 10 mM acetic acid. An energy requirement for [3H]acetic acid uptake was also demonstrated, because metabolic inhibitors (2,4-dinitrophenol and rotenone) reduced significantly the uptake rate (P less than .05). Carbonylcyanide-p-trifluoro-methoxyphenylhydrazone, a protonophore, inhibited significantly the uptake of [3H]acetic acid at medium pH of 5.0 and 6.0, whereas 4,4'-diisothiocyanostilben-2,2'-disulfonic acid did not. Several MCAs inhibited significantly the uptake rate of [3H]acetic acid, whereas di- and tricarboxylic acids did not. The uptake of [3H]acetic acid was competitively inhibited by salicylic acid, with an inhibition constant, Ki, of 3.60 mM, suggesting a common transport system between acetic acid and salicylic acid. Moreover, at the medium pH of 7.4, salicylic acid and valproic acid inhibited significantly the uptake of [3H]acetic acid, demonstrating that the transport of MCA drugs could also be ascribed to the MCA transport system at the physiologic pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective hydrogenolysis of methyl and ethyl acetate in the gas phase on copper and supported Group VIII metal catalysts

Abstract: The selective hydrogenolysis of methyl and ethyl acetate to ethanol over different copper-based and supported Group VIII metal (Pd, Rh, Pt, Co, Ni) catalysts has been studied in the gas phase at 448–623 K and 0.1–6.0 MPa. Measurements of activity and selectivity show that the copper-based catalysts CuO/MgO-SiO 2 , CuO/ZnO/MnO/Al 2 O 3 , and CuO/ZnO/Fe 2 O 3 in particular exhibit very high selectivities for ethanol at nearly complete acetate conversions under moderate reaction conditions. In the case of copper-catalyzed methyl acetate hydrogenolysis kinetic measurements indicated a complex reaction network consisting of consecutive-competitive reactions due to transesterification of methyl acetate to give ethyl acetate, followed by its subsequent hydrogenolysis to ethanol. Therefore, the kinetics of selective hydrogenolysis of ethyl acetate have been studied separately. Kinetic parameters of a power rate law were determined by fitting to conversion versus space time data and made it also possible to describe satisfactorily the complex reaction network. In contrast, supported monometallic catalysts containing Pd, Rh or Ni were found to be ineffective in the hydrogenation of the acyl group due to multiple splitting of C-O and C-C bonds forming light hydrocarbons, acetic acid and carbon oxides. Addition of Zn to Pd/Al 2 O 3 provides a major change towards higher ethanol selectivity. Furthermore, the catalytic properties of mono- and multimetallic Co/TiO 2 catalysts have been investigated. The use of an electropositive metal, such as Fe, for the preparation of a Co-Rh-Fe/TiO 2 catalyst promotes the formation of ethanol from ethyl acetate with substantially higher conversions.

Analysis of condensates from wood smoke : components derived from polysaccharides and lignins

Abstract: A feasibility study has been carried out of the analysis of total condensate (at {minus}50C) of smoke from smoldering combustion of wood. All of the phenol and furan components in the aqueous condensate were extracted into methylene chloride and the extract was analyzed by GC/MS. The same homologues of guaiacol and syringol derived from lignin were detected as have been described in earlier studies, but in addition, a series of furan derivatives were found. The latter are believed to arise from pyrolysis of polysaccharides. The carboxylic acids in the condensates were analyzed by titration and subsequent GC/MS. Acetic acid was the dominant volatile acid found, with a trace of propanoic, but no significant formic acid.

Preparation of cellulose [1-carbon-13]acetates and determination of monomer composition by NMR spectroscopy

Abstract: A series of cellulose acetates labeled at the carbonyl carbons with carbon-13 was prepared by aqueous acid hydrolysis, metal-catalyzed methanolysis, and acetic acid promoted methanolysis of 2,3,6-tri-([1- 13 C]acetyl) cellulose A total of 16 carbonyl carbon resonances were identified in the carbon-13 NMR spectra of cellulose acetates prepared by aqueous acid hydrolysis Fewer carbonyl carbon resonances were found in the carbon-13 NMR spectra of the cellulose acetates prepared by metal-catalyzed methanolysis

Living cationic polymerization of isobutyl vinyl ether by RCOOH/Lewis acid initiating systems: effects of carboxylate ions and Lewis acid activators

Abstract: A series of acetic acid derivatives (RCOOH; R=CF 3 , CCl 3 , CHCl 2 , CH 2 CL, CH 3 ), coupled with ZnCl 2 , induced living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene at 0 o C. The molecular weight distribution of the polymers was very narrow for R=CF 3 and CCl 3 ; it gradually broadened faster the reaction was. With a stronger Lewis acid activator (EtAlCl 2 ) in place of ZnCl 2 , a fast, conventional, nonliving polymerization occurred. These results were discussed on the basis of the nucleophilic interaction between the growing carbocation and the counteranion ( − OCOR...MX n )

The photo-oxidation of acetic acid by oxygen in the presence of titanium dioxide and dissolved copper ions

Abstract: Acetic acid is oxidized by oxygen in the presence of UV light, TiO2 and dissolved copper ions being the catalysis. The reaction rate is zeroth order with respect both to acetic acid and to dissolved oxygen, and is proportional to the absorbed light intensity, with a quantum yield of 0.06. The variation in reaction rate with the concentrations of the different copper species present in the solution, i.e. free ions, Cu(CH3COO)+ and Cu(CH3COO)2, leads us to propose the second of these as the reactive species adsorbed on the TiO2 surface, the diacetato complex (or neutral salt) also being adsorbed on the TiO2 surface, but as a poison. These results extend those already obtained for formic acid and are a part of a general scheme of photo-oxidation of carboxylic acids in the presence of these catalysts.