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  • ? Dissolved organic matter (DOM) and its main constituents carbon (DOC) and nitrogen (DON) represent an important part of the C and N cycles in forest ecosystems. Although many investigations have been addressing this issue, the knowledge on particulate organic matter (0.45 μm < POM < 500 μm) dynamics, its origin and involvement in organic matter cycling in forest ecosystems is still imperfect.
  • ? In this paper, we report on dissolved and particulate organic carbon and nitrogen fractions in throughfall solutions collected from a broadleaved and coniferous forest stand in Central Germany. Over a period of 2.5 y (2005–2007) we followed the concentrations and fluxes of DOM and POM at a mature beech (Fagus sylvatica L.) and a Norway spruce (Picea abies L.) forest site. Bulk and throughfall precipitation were sampled in weekly (2005) and fortnightly (2006–2007) intervals and analyzed for dissolved (< 0.45 μm, filtered) and total (< 500 μm, unfiltered) amounts of organic carbon (DOC, TOC, POC) and nitrogen (TN, DN, PON, NO3-N) species. Proportions of particulate organic C and N were determined by difference between total and dissolved fractions.
  • ? Under spruce, throughfall concentrations of most C and N fractions were twice as high as under beech. At both sites, concentrations and fluxes were significantly higher during the growing than the dormant season. At the broadleaved site, 80% of the annual fluxes of the DOC and TOC and 70% of the DN and TN were released during the growing season, compared to 60% for C and N at the coniferous site. POC under beech contributes with up to 30% to TOC compared to less than 20% at the spruce site.
  • ? We suggest that pollen deposition, insect excretions and accumulated organic matter mobilised by dry/wet precipitation patterns play a supreme role for the formation of DOM and POM in forest canopies. The study demonstrates that the canopy is an important source for POM. Dynamics of DOM and POM are mainly driven by tree species effects and seasonality as well as by biotic agents.
  •   相似文献   
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    Quality changes of vacuum-packed Atlantic mackerel (Scomber scombrus) fillets during 12 months’ frozen storage at ?27°C and 9 days’ chilled storage at +4°C were evaluated. Freezing at ?27°C preserved the long chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs), both in light and dark muscle, vitamin D, and the low molecular weight metabolites (LMW) (studied by high resolution nuclear magnetic resonance spectroscopy, HR NMR). Protein oxidation took place, especially between 1 and 7 months, decreasing water holding capacity and protein extractability. During chilled storage, no lipid or protein oxidation was observed, but lipolysis increased, and several LMW metabolites relevant for sensory and nutritional quality degraded into non-favorable compounds. The content of biogenic amines was high at day 9 (e.g., 18 mg histamine/100 g), jeopardizing safety. Preservation of mackerel fillets by freezing at ?27°C is thus a better option compared to prolonged chilled storage at +4°C; the quality was well preserved for 12 months’ frozen storage.  相似文献   
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    Procyanidin dimers and trimers, needed as reference compounds for biological studies, have been synthesized from various natural sources using a semisynthetic approach and purified by high-speed countercurrent chromatography (HSCCC). In the past, it has been difficult to elucidate the structure of these compounds, especially the determination of the interflavanoid bond. Here, the structure of two B-type procyanidin dimers, with (+)-catechin ((+)-C) in the upper unit, and eight C-type procyanidin trimers, with (-)-epicatechin ((-)-EC) in the upper unit, have been elucidated using low-temperature (1)H NMR spectroscopy, as well as circular dichroism (CD) spectroscopy. This is the first time NOE interactions have been used to characterize the interflavanoid linkage in underivatized procyanidin trimers. Complete analyses of procyanidin C1 (-)-EC-4β→8-(-)-EC-4β→8-(-)-EC, (-)-EC-4β→8-(-)-EC-4β→8-(+)-C, (-)-EC-4β→6-(-)-EC-4β→8-(-)-EC, (-)-EC-4β→6-(-)-EC-4β→8-(+)-C, (-)-EC-4β→8-(-)-EC-4β→6-(-)-EC, (-)-EC-4β→8-(-)-EC-4β→6-(+)-C, (-)-EC-4β→8-(+)-C-4α→8-(-)-EC, procyanidin C4 (-)-EC-4β→8-(+)-C-4α→8-(+)-C, and procyanidin dimers B6 (+)-C-4α→6-(+)-C and B8 (+)-C-4α→6-(-)-EC are presented.  相似文献   
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    Fragaria x ananassa enone oxidoreductase (FaEO), earlier putatively assigned as quinone oxidoreductase, is a ripening-induced, negatively auxin-regulated enzyme that catalyzes the formation of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF), the key flavor compound in strawberry fruit by the reduction of the alpha,beta-unsaturated bond of the highly reactive precursor 4-hydroxy-5-methyl-2-methylene-3(2H)-furanone (HMMF). Here we show that recombinant FaEO does not reduce the double bond of straight-chain 2-alkenals or 2-alkenones but rather hydrogenates previously unknown HMMF derivatives substituted at the methylene functional group. The furanones were prepared from 4-hydroxy-5-methyl-3(2H)-furanone with a number of aldehydes and a ketone. The kinetic data for the newly synthesized aroma-active substrates and products are similar to the values obtained for an enone oxidoreductase from Arabidopsis thaliana catalyzing the alpha,beta-hydrogenation of 2-alkenals. HMMF, the substrate of FaEO that is formed during strawberry fruit ripening, was also detected in tomato and pineapple fruit by HPLC-ESI-MSn and became 13C-labeled when d-[6-13C]-glucose was applied to the fruits, which suggested that a similar HDMF biosynthetic pathway occurs in the different plant species. With a database search (http://ted.bti.cornell.edu/ and http://genet.imb.uq.edu.au/Pineapple/), we identified a tomato and pineapple expressed sequence tag that shows significant homology to FaEO. Solanum lycopersicon EO (SlEO) was cloned from cDNA, and the protein was expressed in Escherichia coli and purified. Biochemical studies confirmed the involvement of SlEO in the biosynthesis of HDMF in tomato fruit.  相似文献   
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    OBJECTIVE: To analyse the association between socio-economic indicators and diet among 2-year-old children, by assessing the independent contribution of parental education and equivalent income to food intake. DESIGN: The analysis was based on data from a prospective birth cohort study. Information on diet was obtained using a semi-quantitative food-frequency questionnaire. Low and high intake of food was defined according to the lowest and the highest quintile of food consumption frequency, respectively. SETTING: Four German cities (Munich, Leipzig, Wesel, Bad Honnef), 1999-2001.Subjects Subjects were 2637 children at the age of 2 years, whose parents completed questionnaires gathering information on lifestyle factors, including parental socio-economic status, household consumption frequencies and children's diet. RESULTS: Both low parental education and low equivalent income were associated with a low intake of fresh fruit, cooked vegetables and olive oil, and a high intake of canned vegetables or fruit, margarine, mayonnaise and processed salad dressing in children. Children with a low intake of milk and cream, and a high intake of hardened vegetable fat, more likely had parents with lower education. Low butter intake was associated with low equivalent income only. CONCLUSIONS: These findings may be helpful for future intervention programmes with more targeted policies aiming at an improvement of children's diets.  相似文献   
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