Poly(ethylene terephthalate) (PETE) packaging is becoming an increasingly popular choice of packaging material for milk, but has the disadvantage of releasing odorous acetaldehyde into food matrices. Sensory detection group thresholds for acetaldehyde in whole, low fat and nonfat unflavored milks were 3939, 4020, and 4040 ppb respectively with no significant difference due to fat level. Chocolate flavored milk and spring water showed detection thresholds levels for acetaldehyde of 10048 and 167 ppb respectively. This information assisted in determining if acetaldehyde migration from the package to the product would influence the flavor of the product. Whole milk was packaged in glass, high density polyethylene (HDPE), amber PETE, clear PETE, and clear PETE with UV light block and was exposed to fluorescent light of 1100-1300 lux (100-120 FC) at 4oC for 18 days. Sensory and chemical analysis and was done on milk from all containers over a period of 18 days. Emphasis was on oxidation, acetaldehyde and lacks freshness off-flavors and byproducts. All volatile flavor compounds studied (acetaldehyde, pentanal, dimethyl disulfide, and hexanal) were increased in light-exposed milk samples. Amber PETE showed the least amount of oxidation off-flavor, while clear PETE with UV block showed significantly less oxidation off-flavor than glass, clear PETE or HDPE on day 7 and 18. Acetaldehyde was not detected by sensory analysis in either light-exposed or light-protected samples. Chemical analysis showed relative acetaldehyde levels in glass (2220 ppb), HDPE (1265 ppb), amber PETE (3397 ppb), clear PETE (2930 ppb), and clear PETE with UV light block (1754 ppb) were all below concentrations found for human flavor threshold. / Master of Science

No description available.

A novel catalytic process for producing high-purity, elevated-pressure hydrogen from synthesis gas was proposed and investigated. The process combines the advantages of low investment and operating costs with the flexibility to adapt to a small-scale operation. The process consists of a loop containing two complementary reactions: ethanol dehydrogenation and acetaldehyde hydrogenation. In one part of the loop, hydrogen is produced by dehydrogenation of ethanol to acetaldehyde. Since acetaldehyde is a liquid under standard conditions, it can be easily separated and pure hydrogen is obtained. In the other part of the loop, hydrogen contained in synthesis gas is reacted with acetaldehyde to produce ethanol and purified carbon monoxide. Ethanol, also a liquid under standard conditions, is easily removed and purified carbon monoxide is obtained, which can be further water-gas shifted to produce more hydrogen. Various dimensionless criteria were evaluated to confirm there was no significant effect of heat and mass transfer limitations and thus the experimental results represent true kinetics. Furthermore, a thermodynamic study was conducted using a Gibbs free energy minimization model to identify the effect of reaction conditions on ethanol/acetaldehyde conversion and determine the thermodynamically favourable operating conditions. Various catalysts were synthesized, characterized and screened for each reaction in a down-flow, fixed-bed quartz reactor. A novel gas chromatography analysis method allowing for an on-line detection of all products was also developed. Unsupported copper in the form of copper foam and copper supported on three different high surface supports were evaluated in ethanol dehydrogenation. Copper foam provided the lowest activity, because of its low surface area. Cu/SiO2 was the most active catalyst for ethanol dehydrogenation. The effects of temperature, pressure, residence time, and feed composition on ethanol conversion and product composition were determined. While increasing temperature or residence time resulted in increased ethanol conversion, elevated pressure and water content in the feed had no effect on ethanol conversion. On the other hand, acetaldehyde selectivity decreased with increasing temperature, pressure and residence time, as acetaldehyde participated in undesirable transformations to secondary products, out of which the most dominant was ethyl acetate. The maximum operating temperature was limited by the stability of the copper catalyst, which deactivated by sintering at temperatures higher than 300°C. The range of temperatures investigated was from 200°C to 350°C, while pressures ranged from atmospheric to 0.5 MPa. For ethanol:water ratios <1, the addition of water to the ethanol feed improved the catalyst stability and acetaldehyde selectivity, but a detrimental effect was observed at higher ratios. The introduction of acetaldehyde into the feed always lowered the conversion, thus indicating a need for stream purification within the loop. An empirical kinetic model was used to determine the activation energy, the order of reaction and the frequency factor. Unsupported and SiO2-supported copper catalysts were compared in acetaldehyde hydrogenation. Pure copper was identified as the best catalyst. Effects of temperature, pressure, residence time, feed composition and catalyst promoter on acetaldehyde conversion and product composition were evaluated. The acetaldehyde hydrogenation was enhanced by increased temperature, pressure and residence time and suppressed in presence of Fe or Zn promoters. Once again, at elevated temperature and residence time, ethanol combined with acetaldehyde to produce undesired ethyl acetate. CO acted as an inert when testing with the pure copper catalyst, but slightly decreased conversion with the supported catalyst. A decrease in conversion was also observed with the introduction of water and ethanol in the feed, once again indicating a requirement for feed purity within the loop. A temperature range of 150-300°C was investigated with catalysts deactivating at temperatures exceeding 250°C. A pressure range identical to ethanol dehydrogenation was used: 0.1-0.5 MPa. Again, an empirical kinetic model allowed determination of the activation energy, the order of reaction and the frequency factor.

A novel catalytic process for producing high-purity, elevated-pressure hydrogen from synthesis gas was proposed and investigated. The process combines the advantages of low investment and operating costs with the flexibility to adapt to a small-scale operation. The process consists of a loop containing two complementary reactions: ethanol dehydrogenation and acetaldehyde hydrogenation. In one part of the loop, hydrogen is produced by dehydrogenation of ethanol to acetaldehyde. Since acetaldehyde is a liquid under standard conditions, it can be easily separated and pure hydrogen is obtained. In the other part of the loop, hydrogen contained in synthesis gas is reacted with acetaldehyde to produce ethanol and purified carbon monoxide. Ethanol, also a liquid under standard conditions, is easily removed and purified carbon monoxide is obtained, which can be further water-gas shifted to produce more hydrogen. Various dimensionless criteria were evaluated to confirm there was no significant effect of heat and mass transfer limitations and thus the experimental results represent true kinetics. Furthermore, a thermodynamic study was conducted using a Gibbs free energy minimization model to identify the effect of reaction conditions on ethanol/acetaldehyde conversion and determine the thermodynamically favourable operating conditions. Various catalysts were synthesized, characterized and screened for each reaction in a down-flow, fixed-bed quartz reactor. A novel gas chromatography analysis method allowing for an on-line detection of all products was also developed. Unsupported copper in the form of copper foam and copper supported on three different high surface supports were evaluated in ethanol dehydrogenation. Copper foam provided the lowest activity, because of its low surface area. Cu/SiO2 was the most active catalyst for ethanol dehydrogenation. The effects of temperature, pressure, residence time, and feed composition on ethanol conversion and product composition were determined. While increasing temperature or residence time resulted in increased ethanol conversion, elevated pressure and water content in the feed had no effect on ethanol conversion. On the other hand, acetaldehyde selectivity decreased with increasing temperature, pressure and residence time, as acetaldehyde participated in undesirable transformations to secondary products, out of which the most dominant was ethyl acetate. The maximum operating temperature was limited by the stability of the copper catalyst, which deactivated by sintering at temperatures higher than 300°C. The range of temperatures investigated was from 200°C to 350°C, while pressures ranged from atmospheric to 0.5 MPa. For ethanol:water ratios <1, the addition of water to the ethanol feed improved the catalyst stability and acetaldehyde selectivity, but a detrimental effect was observed at higher ratios. The introduction of acetaldehyde into the feed always lowered the conversion, thus indicating a need for stream purification within the loop. An empirical kinetic model was used to determine the activation energy, the order of reaction and the frequency factor. Unsupported and SiO2-supported copper catalysts were compared in acetaldehyde hydrogenation. Pure copper was identified as the best catalyst. Effects of temperature, pressure, residence time, feed composition and catalyst promoter on acetaldehyde conversion and product composition were evaluated. The acetaldehyde hydrogenation was enhanced by increased temperature, pressure and residence time and suppressed in presence of Fe or Zn promoters. Once again, at elevated temperature and residence time, ethanol combined with acetaldehyde to produce undesired ethyl acetate. CO acted as an inert when testing with the pure copper catalyst, but slightly decreased conversion with the supported catalyst. A decrease in conversion was also observed with the introduction of water and ethanol in the feed, once again indicating a requirement for feed purity within the loop. A temperature range of 150-300°C was investigated with catalysts deactivating at temperatures exceeding 250°C. A pressure range identical to ethanol dehydrogenation was used: 0.1-0.5 MPa. Again, an empirical kinetic model allowed determination of the activation energy, the order of reaction and the frequency factor.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

No description available.

Extreme thermophiles and hyperthermophiles are microorganisms capable of growing optimally at 65-79??C and 80??C plus, respectively. Many of the enzymes isolated from them are thermostable, which makes them a potential resource for research and industrial applications. An increasing number of hyper/thermophiles is shown to be able to produce ethanol as an end-metabolite. Despite characterization of many alcohol dehydrogenases (ADHs) with a potential role in the production of ethanol, to date there has been no significant progress in identifying the enzymes responsible for the production of acetaldehyde, which is an intermediate in production of ethanol from pyruvate.<br> Pyruvate decarboxylase (PDC encoded by pdc) is a thiamine pyrophosphate (TPP)-containing enzyme responsible for conversion of pyruvate to acetaldehyde in many mesophilic organisms. However, no pdc/PDC homolog has yet been found in fully sequenced genomes of hyper/thermophiles. The only PDC activity reported in hyperthermophiles is a bifunctional, TPP- and CoA-dependent pyruvate ferredoxin oxidoreductase (POR)/PDC enzyme from the hyperthermophilic archaeon Pyrococcus furiosus.<br> The bifunctional and TPP-containing POR/PDC enzyme was isolated and characterized from the ethanol-producing hyperthermophilic archaeon Thermococcus guaymasensis (Topt=88??C), as well as the bacteria Thermotoga hypogea (Topt=70??C) and Thermotoga maritima (Topt=80??C). The T. guaymasensis enzyme was purified anaerobically to homogeneity as judged by SDS-PAGE analysis. POR and PDC activities were co-eluted from each of the chromatographic columns, and the ratio of POR to PDC activities remained constant throughout the purification steps. All of the enzyme activities were CoA- and TPP-dependent and highly sensitive toward exposure to air. The apparent kinetic parameters were determined for the main substrates, including pyruvate and CoA for each activity. Since the genome sequence of T. guaymasensis and T. hypogea were not available, sequences of the genes encoding POR were determined via primer walking and inverse PCR.<br> A novel enzyme capable of catalyzing the production of acetaldehyde from pyruvate in hyperthermophiles was also characterized. The enzyme contained TPP and flavin and was expressed as recombinant histidine-tagged protein in the mesophilic host Escherichia coli. The new enzyme was a bifunctional enzyme catalyzing another reaction as the major reaction besides catalyzing the non-oxidative decarboxylation of pyruvate to acetaldehyde.<br> Another enzyme known to be involved in catalysis of acetaldehyde production from pyruvate is CoA-acetylating acetaldehyde dehydrogenase (AcDH encoded by mhpF and adhE). Pyruvate is oxidized into acetyl-CoA by either POR or pyruvate formate lyase (PFL), and AcDH catalyzes the reduction of acetyl-CoA to acetaldehyde. AcDH is present in some mesophilic (such as clostridia) and thermophilic bacteria (e.g. Geobacillus and Thermoanaerobacter). However, no AcDH gene or protein homologs could be found in the released genomes of hyperthermophiles. Moreover, no such activity was detectable from the cell-free extracts of different hyperthermophiles used in this study.<br> In conclusion, no commonly-known PDCs was found in hyperthermophiles, but two types of acetaldehyde-producing enzymes were present in various bacterial and archaeal hyperthermophiles. Although the deduced amino acid sequences from different hyperthermophiles are quite similar, the levels of POR and PDC activities appeared to vary significantly between the archaeal and bacterial enzymes, which most likely reflects the different physiological implications of each activity.

Thesis (Ph. D.)--Victoria University (Melbourne, Vic.), 2007. / Includes bibliographical references.

Thesis (Ph. D.)--University of Pennsylvania, 1932. / "Reprinted from the Journal of the American chemical society, vol. 54, no. 9."