Potential of gas chromatography-orthogonal acceleration time-of-flight mass spectrometry (GC-oaTOFMS) in flavor research

Gas chromatography-orthogonal acceleration time-of-flight mass spectrometry (GC-oaTOFMS) is an emerging technique offering a straightforward access to a resolving power up to 7000. This paper deals with the use of GC-oaTOFMS to identify the flavor components of a complex seafood flavor extract and to quantify furanones formed in model Maillard reactions. A seafood extract was selected as a representative example for complex food flavors and was previously analyzed using GC-quadrupole MS, leaving several molecules unidentified. GC-oaTOFMS analysis was focused on these unknowns to evaluate its potential in flavor research, particularly for determining exact masses. N-Methyldithiodimethylamine, 6-methyl-5-hepten-2-one, and tetrahydro-2,4-dimethyl-4H-pyrrolo[2,1-d]-1,3,5-dithiazine were successfully identified on the basis of the precise mass determination of their molecular ions and their major fragments. A second set of experiments was performed to test the capabilities of the GC-oaTOFMS for quantification. Calibration curves were found to be linear over a dynamic range of 10(3) for the quantification of furanones. The quantitative data obtained using GC-oaTOFMS confirmed earlier results that the formation of 4-hydroxy-2,5-dimethyl-3(2H)-furanone was favored in the xylose/glycine model reaction and 2(or 5)-ethyl-4-hydroxy-5(or 2)-methyl-3(2H)-furanone in the xylose/alanine model reaction. It was concluded that GC-oaTOFMS may become a powerful analytical tool for the flavor chemist for both identification and quantification purposes, the latter in particular when combined with stable isotope dilution assay.     

Lipase-assisted generation of 2-methyl-3-furanthiol and 2-furfurylthiol from thioacetates

Enzymatic hydrolysis of S-3-(2-methylfuryl) thioacetate and S-2-furfuryl thioacetate using lipase from Candida rugosa produced 2-methyl-3-furanthiol and 2-furfurylthiol, respectively. When reactions were carried out at room temperature and pH 5.8, 2-methyl-3-furanthiol was produced in a optimal yield of 88% after 15 min of reaction, whereas 2-furfurylthiol was obtained in a yield of 80% after 1 h of reaction time. Enzymatic hydrolysis was also performed in n-hexane, n-pentane, and water/propylene glycol mixture. The reaction rates in these media were slower as compared to those in aqueous medium; however, the reaction yields were quite similar. As expected, the stability of the generated 2-methyl-3-furanthiol and 2-furfurylthiol was better in n-hexane, n-pentane, and the water/propylene glycol mixture as compared to that in water or phosphate buffer.     

Species diversity versus phylogenetic diversity: A practical study in the taxonomically difficult genus Dactylorhiza (Orchidaceae)

Setting conservation priorities in taxonomically complex groups such as the orchid genus Dactylorhiza is a difficult task. As an alternative to taxonomic diversity, we used here a molecular phylogenetic analysis and the results of a genetic investigation using plastid microsatellites with an extensive geographic sampling to assess in a more objective way the patterns of diversity within this genus. Although western Europe is thought to be the main diversity centre for the genus due to the large number of species found there, we found higher phylogenetic and genetic diversity as well as higher endemicity in the Caucasus and the Mediterranean Basin, two biodiversity hotspots. Species number seems to be correlated with taxonomic effort, tentatively estimated here by the number of herbaria, and is thus biased and not an appropriate measure of diversity. Our results show that phylogenetic analyses and genetic data obtained with molecular tools can offer an alternative measure of biodiversity that is not sensitive to taxonomic inflation. Conservation of allotetraploid taxa is also discussed, and it is recommended that sites in which polyploids are formed should be conserved rather than any specific allotetraploid taxon.     

Acid pulses from snowmelt at acidic cone pond,New Hampshire

A study was undertaken to examine whether ‘acid pulses’ from snowmelt created permanent changes in a pond's chemistry. Water samples were collected from clearwater acidic Cone Pond in the White Mountain National Forest, New Hampshire. The pond, inlet, and outlet were intensively sampled throughout winter and early spring 1983–84. Thaws brought more H⁺ into upper waters of the pond, but most was gone within a week. In contrast, SO₄ ^2? and Al showed dilution with increased streamflow into the pond, and NO₃ ^? was only detected in ice, slush, and surface waters. Bottom waters were anoxic throughout the winter and had pH 6.0 compared to 4.7 for most of the water column. Alkalinity at the bottom rose from 0 in November 1983 to 190 μeq L^?1 in April 1984. Between November and April the pond gained Al but lost SO₄ ^2? and H⁺. Most of the Al gain came after ice-out when loading through the inlet increased, but during the final snowmelt a temporary increase in Al concentration was also seen throughout the water column.     

Nitric Oxide and Superoxide Anion Production During Heparin‐Induced Capacitation in Cryopreserved Bovine Spermatozoa

The aim of this work was to quantify NO, O₂^? and ONOO^? production during heparin‐induced capacitation of cryopreserved bovine spermatozoa. A time dependent hyperbolic increase was observed for heparin‐dependent capacitation, O₂ uptake, and NO production. Conversely, O₂^? production was increased during the first 15 min of incubation, showing a decrease from this time until 45 min. At 15 min of heparin incubation, a threefold increase in O₂ consumption (5.9 ± 0.6 nmol/min × 10⁷ cells), an enhancement in NO release (1.1 ± 0.2 nmol/min × 10⁷ cells), and a five‐fold increase in O₂^? production (1.3 ± 0.07 nmol/min × 10⁷ cells), were observed. Peroxynitrite production rate was estimated taking into account NO and O₂^? generation and the second‐order rate constant of the reaction between these species. To conclude, heparin‐induced capacitation of cryopreserved bovine spermatozoa activates (i) mitochondrial O₂ uptake by high ADP levels due to increased energy requirements, (ii) NO production by a constitutive NOS and (iii) O₂^? production by a membrane‐bound NAD(P)H oxidase. The products of both enzymes are released to the extracellular space and could be involved in the process of sperm capacitation.     

Thermogenic gas hydrates in the gulf of Mexico

Thermogenic gas hydrates were recovered from the upper few meters of bottom sediments in the northwestern Gulf of Mexico. The hydrates were associated with oil-stained cores at a water depth of 530 meters. The hydrates apparently occur sporadically in seismic "wipeout" zones of sediments in a region of the Gulf continental slope at least several hundred square kilometers in area.