Effect of preparation conditions on release of selected volatiles in tea headspace

The release of volatile compounds from infused tea was monitored using on-line atmospheric pressure chemical ionization (APCI) mass spectrometry. Assignment of the APCI ions to particular compounds was achieved using gas chromatography of tea headspace with dual electron ionization and APCI-MS detectors. Six ions in the APCI spectrum could be assigned to individual compounds, five ions were associated with isobaric compounds (e.g., 2- and 3-methylbutanal and pentanal) or stereoisomers (e.g., heptenals or heptadienals), and a further four ions monitored were identified compounds but with some unknown impurities. Reproducibility of infusion preparation and the analytical system was good with percentage variation values generally below 5%. The analysis was used to study the effect of infusion and holding temperatures on the volatile profile of tea headspace samples, and this was found to be compound-dependent. Both the extraction of volatiles from leaf tea and the release of volatiles into the headspace play a role in creating the aroma profile that the consumer experiences.     

Regional astrocyte allocation regulates CNS synaptogenesis and repair

Astrocytes, the most abundant cell population in the central nervous system (CNS), are essential for normal neurological function. We show that astrocytes are allocated to spatial domains in mouse spinal cord and brain in accordance with their embryonic sites of origin in the ventricular zone. These domains remain stable throughout life without evidence of secondary tangential migration, even after acute CNS injury. Domain-specific depletion of astrocytes in ventral spinal cord resulted in abnormal motor neuron synaptogenesis, which was not rescued by immigration of astrocytes from adjoining regions. Our findings demonstrate that region-restricted astrocyte allocation is a general CNS phenomenon and reveal intrinsic limitations of the astroglial response to injury.     

Isomeric influence on the oxidative coloration of phenolic compounds in a model white wine: comparison of (+)-catechin and (-)-epicatechin

The reactions of (+)-catechin and (-)-epicatechin with glyoxylic acid were studied in a model white wine solution. When the reactions were performed in darkness at 45 degrees C, the (-)-epicatechin concentration decreased more rapidly than that of (+)-catechin, and the (-)-epicatechin sample had twice the 440 nm absorbance of the (+)-catechin sample after the 14 day incubation period. The main pigments generated were identified as xanthylium cation pigments regardless of the isomeric character of the phenolic compound. Using a combination of absorbance and ion current data, the xanthylium cation pigments generated from (-)-epicatechin were found to have combined molar absorptivity coefficients 1.8 times that of the xanthylium cation pigments generated from (+)-catechin. The implication of these results on the development of an index of white wine oxidation susceptibility is discussed.     

Principal component analysis applied to Fourier transform infrared spectroscopy for the design of calibration sets for glycerol prediction models in wine and for the detection and classification of outlier samples

Principal component analysis (PCA) was used to identify the main sources of variation in the Fourier transform infrared (FT-IR) spectra of 329 wines of various styles. The FT-IR spectra were gathered using a specialized WineScan instrument. The main sources of variation included the reducing sugar and alcohol content of the samples, as well as the stage of fermentation and the maturation period of the wines. The implications of the variation between the different wine styles for the design of calibration models with accurate predictive abilities were investigated using glycerol calibration in wine as a model system. PCA enabled the identification and interpretation of samples that were poorly predicted by the calibration models, as well as the detection of individual samples in the sample set that had atypical spectra (i.e., outlier samples). The Soft Independent Modeling of Class Analogy (SIMCA) approach was used to establish a model for the classification of the outlier samples. A glycerol calibration for wine was developed (reducing sugar content < 30 g/L, alcohol > 8% v/v) with satisfactory predictive ability (SEP = 0.40 g/L). The RPD value (ratio of the standard deviation of the data to the standard error of prediction) was 5.6, indicating that the calibration is suitable for quantification purposes. A calibration for glycerol in special late harvest and noble late harvest wines (RS 31-147 g/L, alcohol > 11.6% v/v) with a prediction error SECV = 0.65 g/L, was also established. This study yielded an analytical strategy that combined the careful design of calibration sets with measures that facilitated the early detection and interpretation of poorly predicted samples and outlier samples in a sample set. The strategy provided a powerful means of quality control, which is necessary for the generation of accurate prediction data and therefore for the successful implementation of FT-IR in the routine analytical laboratory.     

Emission rates of N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> from soils with different organic matter content from three long-term fertilization experiments—a laboratory study

Increasing organic matter stocks in soils reduce atmospheric carbon dioxide (CO₂), but they may also promote emissions of nitrous oxide (N₂O) by providing substrates for nitrification and denitrification and by increasing microbial O₂ consumption. The objectives of this study were to determine the effects of fertilization history, which had resulted in different soil organic matter stocks on (1) the emission rates of N₂O and CO₂ at a constant soil moisture content of 60% water-holding capacity, (2) the short-term fluxes of N₂O and CO₂ following the application of different fertilizers (KNO₃ vs. farmyard manure from cattle) and (3) the response to a simulated heavy rainfall event, which increased soil moisture to field capacity. Soil samples from different treatments of three long-term fertilization experiments in Germany (Methau, Spröda and Bad Lauchstädt) were incubated in a laboratory experiment with continuous determination of N₂O and CO₂ emissions and a monitoring of soil mineral N. The long-term fertilization treatments included application of mineral N (Methau and Spröda), farmyard manure + mineral N (Methau and Spröda), farmyard manure deposition in excess (Bad Lauchstädt) and nil fertilization (Bad Lauchstädt). Long-term addition of farmyard manure increased the soil organic C (SOC) content by 55% at Methau (silt loam), by 17% at Spröda (sandy loam) and by 88% at Bad Lauchstädt (silt loam; extreme treatment which does not represent common agricultural management). Increased soil organic matter stocks induced by long-term application of farmyard manure at Methau and Spröda resulted in slightly increased N₂O emissions at a soil moisture content of 60% water-holding capacity. However, the effect of fertilization history and SOC content on N₂O emissions was small compared to the short-term effects induced by the current fertilizer application. At Bad Lauchstädt, high N₂O emissions from the treatment without fertilization for 25 years indicate the importance of a sustainable soil organic matter management to maintain soil structure and soil aeration. Emissions of N₂O following the application of nitrate and farmyard manure differed because of their specific effects on soil nitrate availability and microbial oxygen consumption. At a soil moisture content of 60% water-holding capacity, fertilizer-induced emissions were higher for farmyard manure than for nitrate. At field capacity, nitrate application induced the highest emissions. Our results indicate that feedback mechanisms of soil C sequestration on N₂O emissions have to be considered when discussing options to increase soil C stocks.