Showing papers on "Acetic acid published in 2006"

Rapid determination of short‐chain fatty acids in colonic contents and faeces of humans and rats by acidified water‐extraction and direct‐injection gas chromatography

Abstract: Short-chain fatty acids (SCFAs) have attracted much attention recently because of their positive physiological effects. In this work, a rapid and reliable gas chromatographic method for determination of eight SCFAs, in colonic and faecal samples from rats and humans has been developed and validated. The methodology involves extraction of the SCFAs in water before a direct injection procedure on a FFAP capillary column. A stock standard solution containing acetic acid, propionic acid, n-butyric acid, i-butyric acid, n-valeric acid, i-valeric acid, n-caproic acid and n-heptanoic acid was prepared and used. A high linearity (r2 > 0.9990), low quantification limit (2.38-30.14 microm) and high recovery for most acids were obtained. Acidification of faecal samples was found to be crucial for quantitative determination of the SCFAs, and adjustment of pH to 2-3 was regarded as necessary. Glass wool inserted in the glass liner of the injection port proved effective in preventing the contamination of the column by non-volatiles, and 12% formic acid reduced the ghost peak that appeared gradually after several injections. After validation, the methodology was applied on two faecal samples from rats fed diets containing different amount of dietary fibre and one faecal sample from human fed a normal diet to test the accuracy of the developed method.

Chitosan Film Mechanical and Permeation Properties as Affected by Acid, Plasticizer, and Storage

Abstract: The effects of acid (acetic, formic, lactic, propionic) concentrations, plasticizer concentrations, and storage time (up to 9 wk) on mechanical properties, water vapor permeability, and oxygen permeability of solution-cast chitosan films were determined. Measured water vapor permeability coefficients ranged from 5.35 to 13.20 x 10 -1 g/m.day.atm. Oxygen permeated coefficients ranged from 0.08 to 31.67 x 10 -3 cc O 2 / m.day.atm. Neither property was affected by storage time. Tensile strength (6.85-31.88 Mpa) also was not time dependent, but elongation (14-70%) decreased with storage time. Lactic acid solutions produced the lowest oxygen permeability values, formic acid the highest. Films formed with 7.5% lactic acid solutions had uniquely high values for elongation at break.

Genome-Based Metabolic Engineering of Mannheimia succiniciproducens for Succinic Acid Production

Abstract: Succinic acid is a four-carbon dicarboxylic acid produced as one of the fermentation products of anaerobic metabolism. Based on the complete genome sequence of a capnophilic succinic acid-producing rumen bacterium, Mannheimia succiniciproducens, gene knockout studies were carried out to understand its anaerobic fermentative metabolism and consequently to develop a metabolically engineered strain capable of producing succinic acid without by-product formation. Among three different CO2-fixing metabolic reactions catalyzed by phosphoenolpyruvate (PEP) carboxykinase, PEP carboxylase, and malic enzyme, PEP carboxykinase was the most important for the anaerobic growth of M. succiniciproducens and succinic acid production. Oxaloacetate formed by carboxylation of PEP was found to be converted to succinic acid by three sequential reactions catalyzed by malate dehydrogenase, fumarase, and fumarate reductase. Major metabolic pathways leading to by-product formation were successfully removed by disrupting the ldhA, pflB, pta, and ackA genes. This metabolically engineered LPK7 strain was able to produce 13.4 g/liter of succinic acid from 20 g/liter glucose with little or no formation of acetic, formic, and lactic acids, resulting in a succinic acid yield of 0.97 mol succinic acid per mol glucose. Fed-batch culture of M. succiniciproducens LPK7 with intermittent glucose feeding allowed the production of 52.4 g/liter of succinic acid, with a succinic acid yield of 1.16 mol succinic acid per mol glucose and a succinic acid productivity of 1.8 g/liter/h, which should be useful for industrial production of succinic acid.

Polyaniline nanotubes: conditions of formation

Abstract: The courses of aniline oxidation with ammonium peroxydisulfate in aqueous solutions of strong (sulfuric) and in weak (acetic) acids, followed by temperature and acidity changes, are different. In solutions of sulfuric acid, granular polyaniline (PANI) was produced; in solutions of acetic acid, PANI nanotubes were obtained. The external diameter of the nanotubes was 100–300 nm, the internal cavity 20–100 nm, and the length extended to several micrometres. The morphology of PANI, granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. PANI nanotubes were also produced when aniline was oxidized in the absence of any acid. The bulk conductivity of PANI prepared in solutions of acetic acid was 0.08–0.27 S cm−1, depending on the acid concentration. Protonated PANI prepared in sulfuric and acetic acids were deprotonated with ammonium hydroxide to obtain PANI bases and the ammonium salt of the protonating acid. FTIR spectroscopy showed the differences in the molecular structure of the PANI bases. Irrespective of whether the polymerization was performed in solutions of sulfuric or acetic acid, PANI had hydrogen sulfate counter-ions only. The PANI morphology is thus not controlled by the nature of counter-ions. The acidity of the reaction medium determines the protonation of monomer, oligomer and polymer species. The chemistry of aniline oxidation is likely to be affected especially by the protonation of an intermediate in the pernigraniline form. It is proposed that, in the course of aniline oxidation, pH-dependent self-assembly of aniline oligomers predetermines the final PANI morphology. Copyright © 2005 Society of Chemical Industry

Effect of water on sulfuric acid catalyzed esterification

Abstract: This paper reports on an investigation into the impact of water on liquid-phase sulfuric acid catalyzed esterification of acetic acid with methanol at 60 °C. In order to diminish the effect of water on the catalysis as a result of the reverse reaction, initial reaction kinetics were measured using a low concentration of sulfuric acid (1 × 10 −3 M) and different initial water concentrations. It was found that the catalytic activity of sulfuric acid was strongly inhibited by water. The catalysts lost up to 90% activity as the amount of water present increased. The order of water effect on reaction rate was determined to be −0.83. The deactivating effect of water also manifested itself by changes in the activation energy and the pre-exponential kinetic factor. The decreased activity of the catalytic protons is suggested to be caused by preferential solvation of them by water over methanol. A proposed model successfully predicts esterification rate as reaction progresses. The results indicate that, as esterification progresses and byproduct water is produced, deactivation of the sulfuric acid catalyst occurs. Autocatalysis, however, was found to be hardly impacted by the presence of water, probably due to compensation effects of water on the catalytic activity of acetic acid, a weak acid.

Reforming reactions of acetic acid on nickel catalysts over a wide temperature range

Abstract: Catalytic steam reforming of bio-oil, a liquid derived from pyrolysis of biomass, may be a viable process of renewable hydrogen production. Acetic acid is one of the major constituents of bio-oil, and for this reason, it is used as a model compound to study its reaction network under steam reforming conditions over Al2O3 and La2O3, and Ni catalyst supported on La2O3/Al2O3 carrier, employing transient and steady-state techniques. It is found that acetic acid interacts strongly with the Al2O3 carrier and less strongly with La2O3. Decomposition reactions as well as the ketonization reaction take place, especially at intermediate temperatures. In the presence of Ni, catalytic activity is shifted toward lower temperatures. Nickel promotes steam reforming reactions and retards the rate of carbon deposition onto the catalyst surface. It is also found that carbon formation is affected by reaction temperature, the HAc/H2O ratio and catalyst composition. Carbon deposition is favoured at low reaction temperatures and at high HAc/H2O ratio.

Process for producing ethanol from corn dry milling

Abstract: A process for producing ethanol by the conversion of carbohydrates from a corn dry milling process in which the bottoms fraction from distillation of ethanol in a conventional yeast fermentation is used in a process including a combination of biochemical and synthetic conversions. The process results in high yield ethanol production with concurrent production of high value coproducts. An acetic acid intermediate is produced from bottoms fraction, followed by conversion of the acetic acid into ethanol using esterification and hydrogenation reactions. Coproducts of the process include a high protein content solids fraction produced in the fermentation.

Dietary acetic acid reduces serum cholesterol and triacylglycerols in rats fed a cholesterol-rich diet.

Abstract: To investigate the efficacy of the intake of vinegar for prevention of hyperlipidaemia, we examined the effect of dietary acetic acid, the main component of vinegar, on serum lipid values in rats fed a diet containing 1 % (w/w) cholesterol. Animals were allowed free access to a diet containing no cholesterol, a diet containing 1 % cholesterol without acetic acid, or a diet containing 1 % cholesterol with 0.3 % (w/w) acetic acid for 19 d. Then, they were killed after food deprivation for 7 h. Cholesterol feeding increased serum total cholesterol and triacylglycerol levels. Compared with the cholesterol-fed group, the cholesterol and acetic acid-fed group had significantly lower values for serum total cholesterol and triacylglycerols, liver ATP citrate lyase (ATP-CL) activity, and liver 3-hydroxy-3-methylglutaryl-CoA content as well as liver mRNA levels of sterol regulatory element binding protein-1, ATP-CL and fatty acid synthase (P<0.05). Further, the serum secretin level, liver acyl-CoA oxidase expression, and faecal bile acid content were significantly higher in the cholesterol and acetic acid-fed group than in the cholesterol-fed group (P<0.05). However, acetic acid feeding affected neither the mRNA level nor activity of cholesterol 7alpha-hydroxylase. In conclusion, dietary acetic acid reduced serum total cholesterol and triacylglycerol: first due to the inhibition of lipogenesis in liver; second due to the increment in faecal bile acid excretion in rats fed a diet containing cholesterol.

Formation of Acetic Acid by Aqueous‐Phase Oxidation of Ethanol with Air in the Presence of a Heterogeneous Gold Catalyst

Abstract: Bioethanol is produced by fermentation of biomass in increasing amounts to meet the growing demands for CO2neutral transportation fuels and to eventually remove the dependence on fossil fuels. However, bioethanol could also find use as a versatile, sustainable chemical feedstock. Herein, it is shown that it is possible to selectively oxidize ethanol into acetic acid in aqueous solution using air as the oxidant with a heterogeneous gold catalyst at temperatures of about 423 K and O2 pressures of 0.6 MPa. This reaction proceeds readily in aqueous acidic media and yields of up to 90% are achieved, with CO2 as the only major by-product. Thus, it constitutes a very simple, green route to acetic acid. The oxidation of ethanol by air into acetic acid over platinum was among the first heterogeneously catalyzed reactions to be reported. The initial discovery was made by D.bereiner about two centuries ago, even before the term catalysis was coined. So far, the reaction has not been used for large-scale production of acetic acid. Instead, three other routes to acetic acid have found industrial application: fermentation (vinegar), catalytic liquid-phase oxidation of butane, naphtha, or acetaldehyde, and the carbonylation of methanol, which has recently become the most important. In the most widely used industrial processes today, the feedstock is almost exclusively derived from fossil fuels. Thus, the production of acetic acid consumes fossil fuels and therefore contributes slightly to increasing CO2 levels in the atmosphere, and, more importantly, the cost of acetic acid is strongly dependent on the price of the fossil fuels. Therefore, it is interesting that the cost of renewable feedstocks has decreased dramatically relative to fossil fuel feedstocks over the last four decades. Specifically, the cost of corn relative to oil has decreased fivefold from 1950 to 2005. Today, bioethanol is mostly produced by fermentation of starchcontaining crops, such as corn or sugar cane, but it seems likely that cellulose-rich agricultural waste will gain importance as a feedstock in the future. Therefore, and also because of the continuing technological improvements of the production process, the cost of bioethanol is expected to decrease. Thus, with increasing fossil fuel prices, the production of acetic acid from bioethanol will become increasingly favorable compared to current fossil fuel-based methods. Clearly, this development requires that an active and selective catalyst for oxidation of ethanol with dioxygen to form acetic acid [Eq. (1)] is available.

Comparison of commercial solid acid catalysts for the esterification of acetic acid with butanol

Abstract: Esterification of acetic acid with butanol has been studied in a heterogeneous reaction system, using a variety of solid acid catalysts. Comparative esterification experiments have been carried out using the homogeneous catalysts sulphuric acid, p -toluenesulphuric acid and a heteropolyacid. The catalysts have been characterised using gas adsorption analysis (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM) and temperature-programmed decomposition (TPD) techniques. The weight-based activity of the heterogeneous catalysts decreases in the following order: Smopex-101 > Amberlyst 15 > sulphated ZrO 2 > H-USY-20 > H-BETA-12.5 > H-MOR-45 > Nb 2 O 5 > H-ZSM-5-12.5. The low activity of ZSM-5 is a result of internal diffusion limitations in the medium sized pores of this zeolite type material. For H-MOR the low activity can be explained by pore blocking in the one-dimensional H-MOR channels. For the H-USY-type zeolites, the influence of the Si/Al ratio on catalytic activity has been examined. Although the amount of acid sites decreases with an increase in the Si/Al ratio, an optimum Si/Al ratio of 20 has been found. The activity of sulphated zirconia shows an optimum calcination temperature, even though both the amount and acidity of the acid sites increase monotonically with calcination temperature. Most likely, at higher calcination temperatures Lewis acid sites are formed and Bronsted acid sites are removed. As Bronsted acid sites are essential for catalysis of esterification reactions this explains the decrease in activity.

Effects of Alkaline and Acid Pretreatments on Alaska Pollock Skin Gelatin Extraction

Abstract: Pretreatments with different alkalis and acids at different concentrations were used to determine their effects on gelatin extraction from Alaska pollock skin. The alkaline pretreatments with the OH concentrations lower than 0.5 mol/L removed noncollagenous proteins without significant loss of skin collagen. The acid pretreatments caused loss of collagen, even using a weak acid with a low H concentration at a low temperature. The presence of proteases might cause degradation of gelatin extract, but the pretreatments with NaOH or Ca(OH)2 at 0.1 mol/L OH concentration, or acetic acid at 0.05 mol/L H concentration could significantly decrease the degradation by proteases. The combination of an alkaline pretreatment followed by an acid pretreatment not only removed the noncollagenous proteins, but also provided the proper pH condition for extraction, during which some cross-linkages could be further destroyed but with less breakage of polypeptide chains.

Determination of formic-acid and acetic acid concentrations formed during hydrothermal treatment of birch wood and its relation to colour, strength and hardness

Abstract: Formation of benzyl esters from acetic and formic acids during heat treatment of birch at 160–200°C has been studied by gas chromatography. High concentrations of formic and acetic acids formed by the wood itself during hydrothermal treatment were found. The concentrations of acids increased with both treatment time and temperature. The maximum formic- and acetic acid concentrations found at 180°C and after 4 h of treatment performed in this work were 1.1 and 7.2%, based on dry-weight wood, respectively. The treated wood material was characterised by mechanical testing [bending tests perpendicular to the grain, modulus of rupture, modulus of elasticity, Brinell hardness, impact bending and colour measurements (CIE colour space)]. The experiments, where high concentration of acids was formed, showed severe losses in mass and mechanical strength. Indications of possible enhanced mechanical properties for the treated, compared with untreated birch wood were found around 180–200°C at short treatment times. This paper discusses possible degradation reactions coupled with the colour and mechanical properties in relation to acid formation, and suggestions for process optimisations.

Yeast genes involved in response to lactic acid and acetic acid: acidic conditions caused by the organic acids in Saccharomyces cerevisiae cultures induce expression of intracellular metal metabolism genes regulated by Aft1p.

Abstract: Using two types of genome-wide analysis to investigate yeast genes involved in response to lactic acid and acetic acid, we found that the acidic condition affects metal metabolism. The first type is an expression analysis using DNA microarrays to investigate 'acid shock response' as the first step to adapt to an acidic condition, and 'acid adaptation' by maintaining integrity in the acidic condition. The other is a functional screening using the nonessential genes deletion collection of Saccharomyces cerevisiae. The expression analysis showed that genes involved in stress response, such as YGP1, TPS1 and HSP150, were induced under the acid shock response. Genes such as FIT2, ARN1 and ARN2, involved in metal metabolism regulated by Aft1p, were induced under the acid adaptation. AFT1 was induced under acid shock response and under acid adaptation with lactic acid. Moreover, green fluorescent protein-fused Aft1p was localized to the nucleus in cells grown in media containing lactic acid, acetic acid, or hydrochloric acid. Both analyses suggested that the acidic condition affects cell wall architecture. The depletion of cell-wall components encoded by SED1, DSE2, CTS1, EGT2, SCW11, SUN4 and YNL300W and histone acetyltransferase complex proteins encoded by YID21, EAF3, EAF5, EAF6 and YAF9 increased resistance to lactic acid. Depletion of the cell-wall mannoprotein Sed1p provided resistance to lactic acid, although the expression of SED1 was induced by exposure to lactic acid. Depletion of vacuolar membrane H+-ATPase and high-osmolarity glycerol mitogen-activated protein kinase proteins caused acid sensitivity. Moreover, our quantitative PCR showed that expression of PDR12 increased under acid shock response with lactic acid and decreased under acid adaptation with hydrochloric acid.

Catalytic carbonylation reactions

Abstract: Hydroformylation.- Asymmetric Hydroformylation.- Synthetic Applications of Tandem Reaction Sequences Involving Hydroformylation.- Hydroxy- and Alkoxycarbonylations of Alkenes and Alkynes.- Carbonylation of Ethene in Methanol Catalysed by Cationic Phosphine Complexes of Pd(II): from Polyketones to Monocarbonylated Products.- The Pauson-Khand Reaction.- Acetic Acid Synthesis by Catalytic Carbonylation of Methanol.- Carbonylations of Aldehydes.- Carbonylation of Epoxides.- Oxidative Carbonylations.

Effect of pH and lactic or acetic acid on ethanol productivity by Saccharomyces cerevisiae in corn mash

Abstract: The effects of lactic and acetic acids on ethanol production by Saccharomyces cerevisiae in corn mash, as influenced by pH and dissolved solids concentration, were examined. The lactic and acetic acid concentrations utilized were 0, 0.5, 1.0, 2.0, 3.0 and 4.0% w/v, and 0, 0.1, 0.2, 0.4, 0.8 and 1.6% w/v, respectively. Corn mashes (20, 25 and 30% dry solids) were adjusted to the following pH levels after lactic or acetic acid addition: 4.0, 4.5, 5.0 or 5.5 prior to yeast inoculation. Lactic acid did not completely inhibit ethanol production by the yeast. However, lactic acid at 4% w/v decreased (P<0.05) final ethanol concentration in all mashes at all pH levels. In 30% solids mash set at pH ≤5, lactic acid at 3% w/v reduced (P<0.05) ethanol production. In contrast, inhibition by acetic acid increased as the concentration of solids in the mash increased and the pH of the medium declined. Ethanol production was completely inhibited in all mashes set at pH 4 in the presence of acetic acid at concentrations ≥0.8% w/v. In 30% solids mash set at pH 4, final ethanol levels decreased (P<0.01) with only 0.1% w/v acetic acid. These results suggest that the inhibitory effects of lactic acid and acetic acid on ethanol production in corn mash fermentation when set at a pH of 5.0–5.5 are not as great as that reported thus far using laboratory media.

Of the Major Phenolic Acids Formed during Human Microbial Fermentation of Tea, Citrus, and Soy Flavonoid Supplements, Only 3,4-Dihydroxyphenylacetic Acid Has Antiproliferative Activity

Abstract: Dietary flavonoids are poorly absorbed from the gastrointestinal tract Colonic bacteria convert flavonoids into smaller phenolic acids (PA), which can be absorbed into the circulation and may contribute to the chemopreventive activity of the parent compounds The purpose of our study was to determine whether flavonoids from green and black tea (GT, BT), citrus fruit with rutin (CF+R) and soy (S) supplements exposed to the same conditions in a dynamic in vitro model of the colon (TIM-2) will form the same phenolic acid products of microbial metabolism About 600 mg of flavonoids from GT, BT, CF+R and S extracts were infused at t = 0 and 12 h into the TIM-2 Samples from the lumen and dialysate were collected at t = 0,4,8,12,16,24 and 28h The flavonoid and PA concentrations were measured by HPLC and GC-MS GT, BT, and CF+R formed 3-methoxy-4-hydroxyphenylacetic acid (3M4HPAA), 4-hydroxyphenyl acetic acid (4HPAA), 3,4-dihydroxyphenylacetic acid (3,4DHPAA), and 3-(3-hydroxyphenyl) propionic acid (3,3HPPA) BT flavonoids were also metabolized to 2,4,6-trihydroxybenzoic acid (2,4,6THBA) and CF+R flavonoids to 3-(4-hydroxy-3-methoxyphenyl) propionic acid (3,4H3MPPA), 3-hydroxyphenyl acetic acid (3HPAA) and a small amount of hippuric acid After S infusion, we found 3M4HPAA and 4HPAA only Among these phenolic acids, only 3,4DHPAA exhibited antiproliferative activity in prostate and colon cancer cells 3,4DHPAA was significantly (P < 0005) more inhibitory in colon cancer cells (HCT116) compared with an immortalized normal intestinal epithelial cell line (IEC6) In summary, fermentation by intestinal microbes of GT, BT, C+R, and S flavonoids resulted in the conversion to the same major phenolic acids © 2006 American Society for Nutrition

Effect of acetyl groups on enzymatic hydrolysis of cellulosic substrates

Abstract: Evidence showed that acetyl groups introduced during acetic acid delignification was a primary cause of the poor enzymatic digestibility of acetic acid pulp. The inhibition by acetyl groups could be removed by saponification. Acetyl groups might inhibit the enzymes by interfering with the productive binding (hydrogen bonds) between cellulose and the catalytic domain of cellulases, by affecting the binding of CBD to cellulose, or by increasing the diameter of the cellulose chain.