| 1. |
- Beuchat, L. R., et al.
(author)
-
Performance of mycological media in enumerating desiccated food spoilage yeasts : an interlaboratory study
- 2001
-
In: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 70:1-2, s. 89-96
-
Journal article (peer-reviewed)abstract
- Dichloran 18% glycerol agar (DG18) was originally formulated to enumerate nonfastidious xerophilic moulds in foods containing rapidly growing Eurotium species. Some laboratories are now using DG18 as a general purpose medium for enumerating yeasts and moulds, although its performance in recovering yeasts from dry foods has not been evaluated. An interlaboratory study compared DG18 with dichloran rose bengal chloramphenicol agar (DRBC), plate count agar supplemented with chloramphenicol (PCAC), tryptone glucose yeast extract chloramphenicol agar (TGYC), acidified potato dextrose agar (APDA), and orange serum agar (OSA) for their suitability to enumerate 14 species of lyophilized yeasts. The coefficient of variation for among-laboratories repeatability within yeast was 1.39% and reproducibility of counts among laboratories was 7.1%. The order of performance of media for recovering yeasts was TGYC > PCAC = OSA > APDA > DRBC > DG18. A second study was done to determine the combined effects of storage time and temperature on viability of yeasts and suitability of media for recovery. Higher viability was retained at - 18 degreesC than at 5 degreesC or 25 degreesC for up to 42 weeks, although the difference in mean counts of yeasts stored at - 18 degreesC and 25 degreesC was only 0.78 log(10) cfu/ml of rehydrated suspension. TGYC was equal to PCAC and superior to the other four media in recovering yeasts stored at - 18 degreesC, 5 degreesC, or 25 degreesC for up to 42 weeks. Results from both the interlaboratory study and the storage study support the use of TGYC for enumerating desiccated yeasts. DG18 is not recommended as a general purpose medium for recovering yeasts from a desiccated condition.
|
|
| 2. |
- Busch, S., et al.
(author)
-
Ion acceleration with ultrafast lasers
- 2003
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:19, s. 3354-3356
-
Journal article (peer-reviewed)abstract
- Hot-electron confinement can build up fields capable of accelerating ions up to MeV energies when an ultrashort 35-fs laser pulse at similar to2x10(18) W/cm(2) interacts with a small spherical target. Singly charged ions with different masses have similar energies. A simple phenomenological model describes how ultrashort and less-energy-consumptive pulses drive ions to MeV energies. The energetic and spatial-emission characteristics of protons, deuterons and oxygen ions released from water and heavy-water droplets of similar to15 mum in size was determined for this interaction scenario.
|
|
| 3. |
- Schnurer, M., et al.
(author)
-
Influence of laser pulse width on absolute EUV-yield from Xe-clusters
- 2001
-
In: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 14:3, s. 331-335
-
Journal article (peer-reviewed)abstract
- Using 50 fs (similar to 2 x 10(18) W/cm(2)) and 2 ps (similar to 5 x 10(16) W/cm(2)) pulses from a Ti:Sa multi-TW laser at 800 nm wavelength large Xe-clusters (10(5)...10(6) atoms per cluster) have been excited. Absolute yield measurements of EUV-emission in a wavelength range between 10 nm and 15 nm in combination with cluster target variation were carried out. The ps-laser pulse has resulted in about 30% enhanced and spatially more uniform EUV-emission compared to fs-laser excitation. Circularly polarized laser light instead of linear polarization results in enhanced emission which is probably caused by electrons gaining higher energies by the polarization dependent optical field ionization process. An absolute emission efficiency at 13.4 nm of up to 0.8% in 2 pi sr and 2.2% bandwidth has been obtained.
|
|
| 4. |
- Druvefors, U., et al.
(author)
-
Efficacy of the biocontrol yeast Pichia anomala during long-term storage of moist feed grain under different oxygen and carbon dioxide regimens
- 2002
-
In: FEMS yeast research (Print). - 1567-1356 .- 1567-1364. ; 2:3, s. 389-394
-
Journal article (peer-reviewed)abstract
- The yeast Pichia anomala inhibits the spoilage mold Penicillium roqueforti in laboratory experiments with high-moisture wheat in malfunctioning airtight storage. The ability of P. anomala to prevent mold growth during 14 months of grain storage was evaluated in outdoor silos with different air permeabilities. Freshly harvested wheat in 160-kg portions was inoculated with 102 colony-forming units (cfu) g-1 P. roqueforti, alone or together with 104 cfu g-1 P. anomala. During the first month P. anomala increased to about 106 cfu g-1 in the treated silos to reach 107 cfu g-1 after 9 months. Naturally occurring P. anomala in the untreated silos increased from 102 to about 103 cfu g-1 during the first month and reached the same level as the treated silos after 9 months. Oxygen levels were reduced below the detection limit within 1 day, while carbon dioxide levels increased to 80-90% during the first month. P. roqueforti did not grow in wheat treated with P. anomala, regardless of silo permeability, but had increased to 105 cfu g-1 in the untreated silos after 14 months of storage. © 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.
|
|
| 5. |
- Fredlund, E., et al.
(author)
-
Metabolite profiles of the biocontrol yeast Pichia anomala J121 grown under oxygen limitation
- 2004
-
In: Applied Microbiology and Biotechnology. - : Springer. - 0175-7598 .- 1432-0614. ; 64:3, s. 403-409
-
Journal article (peer-reviewed)abstract
- The biocontrol yeast Pichia anomala J121 prevents mould growth during the storage of moist grain under low oxygen/high carbon dioxide conditions. Growth and metabolite formation of P. anomala was analyzed under two conditions of oxygen limitation: (a) initial aerobic conditions with restricted oxygen access during the growth period and (b) initial microaerobic conditions followed by anaerobiosis. Major intra- and extracellular metabolites were analyzed by high-resolution magic-angle spinning (HR-MAS) NMR and HPLC, respectively. HR-MAS NMR allows the analysis of major soluble compounds inside intact cells, without the need for an extraction step. Biomass production was higher in treatment (a), whereas the specific ethanol production rate during growth on glucose was similar in both treatments. This implies that oxygen availability affected the respiration and not the fermentation of the yeast. Following glucose depletion, ethanol was oxidized to acetate in treatment (a), but continued to be produced in (b). Arabitol accumulated in the culture substrate of both treatments, whereas glycerol only accumulated in treatment (b). Trehalose, arabitol, and glycerol accumulated inside the cells in both treatments. The levels of these metabolites were generally significantly higher in treatment (b) than in (a), indicating their importance for P. anomala during severe oxygen limitation/anaerobic conditions.
|
|
| 6. |
- Fredlund, Elisabeth, et al.
(author)
-
Oxygen- and glucose-dependent regulation of central carbon metabolism in Pichia anomala
- 2004
-
In: Applied and Environmental Microbiology. - : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 70:10, s. 5905-5911
-
Journal article (peer-reviewed)abstract
- We investigated the regulation of the central aerobic and hypoxic metabolism of the biocontrol and non-Saccharomyces wine yeast Pichia anomala. In aerobic batch culture, P. anomala grows in the respiratory mode with a high biomass yield (0.59 g [dry weight] of cells g of glucose(-1)) and marginal ethanol, glycerol, acetate, and ethyl acetate production. Oxygen limitation, but not glucose pulse, induced fermentation with substantial ethanol production and 10-fold-increased ethyl acetate production. Despite low or absent ethanol formation, the activities of pyruvate decarboxylase and alcohol dehydrogenase were high during aerobic growth on glucose or succinate. No activation of these enzyme activities was observed after a glucose pulse. However, after the shift to oxygen limitation, both enzymes were activated threefold. Metabolic flux analysis revealed that the tricarboxylic acid pathway operates as a cycle during aerobic batch culture and as a two-branched pathway under oxygen limitation. Glucose catabolism through the pentose phosphate pathway was lower during oxygen limitation than under aerobic growth. Overall, our results demonstrate that P. anomala exhibits a Pasteur effect and not a Crabtree effect, i.e., oxygen availability, but not glucose concentration, is the main stimulus for the regulation of the central carbon metabolism.
|
|
| 7. |
- Ter-Avetisyan, S., et al.
(author)
-
Absolute extreme ultraviolet yield from femtosecond-laser-excited Xe clusters
- 2001
-
In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 6403:3
-
Journal article (peer-reviewed)abstract
- Large Xe clusters (10(5)-10(6) atoms per cluster) have been irradiated with ultrashort (50 fs) and high-intensity (similar to2 x 10(18) W/cm(2)) pulses from a Ti:sapphire multi-TW laser at 800 nm wavelength. Scaling and absolute yield measurements of extreme ultraviolet (EUV) emission in a wavelength range between 7 and 15 nm in combination with cluster target characterization have been used for yield optimization. Maximum emission as a function of the backing pressure and a spatial emission anisotropy covering a factor of two at optimized yields is discussed with a simple model of the source geometry and EUV-radiation absorption. Circularly polarized laser light instead of linear polarization results in a factor of 2.5 higher emission in the 11 to 15 nm wavelength range. This indicates the initial influence of optical-field ionization for the interaction parameter range used and contrasts to collisional heating that seems to influence preferentially higher ionization. Absolute emission efficiency at 13.4 nm of up to 0.5% in 2 pi sr and 2.2% bandwidth has been obtained.
|
|
| 8. |
- Ter-Avetisyan, S., et al.
(author)
-
Efficient extreme ultraviolet emission from xenon-cluster jet targets at high repetition rate laser illumination
- 2003
-
In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 94:9, s. 5489-5496
-
Journal article (peer-reviewed)abstract
- We studied extreme ultraviolet (EUV) emission from Xe cluster jet targets irradiated with high repetitive ps and ns laser pulses in the intensity range between 10(11) and 10(15) W/cm(2). It was found that at fixed intensity the conversion efficiency of the laser energy into the EUV emission is higher for ns pulses. In the intensity range used no saturation of the 13.4 nm signal could be reached. At ns pulse duration a conversion efficiency 0.26%@13.4 nm in 2pi steradian and 2.2% bandwidth was reached. The laser energy deposition is discussed in relation to the plasma dynamics of the cluster target. We demonstrated that due to the high flow velocity of the cluster jet target an exposition with laser pulses up to 125 kHz repetition rate is possible without any degradation of the EUV emission efficiency. Both the high conversion efficiency and the high repetition rate make this Xe target attractive for an EUV source with high average EUV power.
|
|
