A detailed size separation of particulate organic matter (POM) from soils amended with straw from Hordeum vulgare or Vicia sativa revealed that the loss of C during the first 56 days of incubation mainly occurred from particles >2,000 μm, without a concomitant
reduction in the size of these large particles. Preliminary studies of POM from non-amended soil had shown that the stable
heavy (>1.4 g cm–3) POM fraction was mainly (>80%) composed of particles <400 μm, whereas the light fraction was dominated by larger particles
(>80%). Therefore we decided to compare the POM <1.4 g cm3 with POM >400 μm. There was a very close relationship between POM>400 μm and POM <1.4 g cm–3 with regard to amounts of C and N, as well as the appearance of these fractions under the microscope. Similarly there was
a close relationship between changes in the C content of the POM fractions and the CO2 respired, and this was also the case when comparing changes in POM-N with net N mineralization. This indicated that the biological
activity during decomposition was actually localized in the POM. Due to the lighter workload and lower expenditure for reagents
in connection with size separation of POM, we recommend the size separation procedure in connection with studies of residue
decomposition in arable systems.
Received: 23 May 2000 相似文献
Polyunsaturated fatty acids (PUFAs) and exercise-induced stress are known to increase the oxidative susceptibility of lipids in muscle tissue. In contrast, antioxidative enzymes, e.g., catalase, superoxide dismutase, and glutathione peroxidase, are known to help sustain the delicate oxidative balance in biological tissue upon the application of stressors. The present study investigates the combined effect of different diet-induced muscle PUFA contents and preslaughter stress on the activity of antioxidative muscle enzymes and the oxidative stability of cooked meat. An increased content of unsaturated fatty acids in the tissue led to a decreased activity of lactate dehydrogenase in the plasma, indicating increased cell integrity. Catalase activity in the muscle tissue increased with increasing PUFA levels. However, this upregulation in antioxidative status of the muscle could not counteract the subsequent development of accelerated lipid oxidation in cooked meat as measured in terms of thiobarbituric acid reactive substances. Moreover, preslaughter stress induced increasing oxidative changes with elevated PUFA levels in the muscle tissue. 相似文献
Heparan and chondroitin sulfate proteoglycans (HSPGs and CSPGs, respectively) regulate numerous cell surface signaling events, with typically opposite effects on cell function. CSPGs inhibit nerve regeneration through receptor protein tyrosine phosphatase sigma (RPTPσ). Here we report that RPTPσ acts bimodally in sensory neuron extension, mediating CSPG inhibition and HSPG growth promotion. Crystallographic analyses of a shared HSPG-CSPG binding site reveal a conformational plasticity that can accommodate diverse glycosaminoglycans with comparable affinities. Heparan sulfate and analogs induced RPTPσ ectodomain oligomerization in solution, which was inhibited by chondroitin sulfate. RPTPσ and HSPGs colocalize in puncta on sensory neurons in culture, whereas CSPGs occupy the extracellular matrix. These results lead to a model where proteoglycans can exert opposing effects on neuronal extension by competing to control the oligomerization of a common receptor. 相似文献
Autofluorescence of salmon and cod muscle was measured and compared with autofluorescence of collagen type I and type V. Similarities between fluorescence of fish muscle and collagen were found in that the same peaks were obtained around 390, 430, and 480 nm. These similarities are supported by principal component analyses. Texture and gaping score were predicted from the fluorescence spectra by partial least-squares regression. However, the predictions did not perform well. Relating fluorescence to the gaping score gave a prediction error of 0.91 and a correlation of 0.43 when measuring gaping on a scale from 0 to 5. There was no relation between texture and fluorescence spectra. Fluorescence of fish muscle could be related to the storage time. However, this relation seemed not to be induced by changes in collagen. 相似文献
The overall objective of this research was to find a new way to valorize rye bran, by producing a gellifier from the enzymatic solubilization of arabinoxylans (AX). The effects of three pure endo-xylanases from Aspergillus niger (Xyl-1), Talaromyces emersonii (Xyl-2), and Bacillus subtilis (Xyl-3) and of Grindamyl S100 (GS100), a commercial enzyme preparation containing a Xyl-1 type endo-xylanase, were tested on rye bran to study the solubilization of water-unextractable arabinoxylans (WUAX). Eight different extrusion-treated rye brans were also used as substrates to find the best physical treatment to facilitate enzymatic arabinoxylan (AX) solubilization. Arabinoxylans were better solubilized from the bran extruded at high temperature using Xyl-3. This enzyme was then tested in combination with pure (1,4)-beta-d-arabinoxylan arabinofuranohydrolase (AXH) and endo-beta-d-glucanase or ferulic acid esterase (FAE), from A. niger. Only beta-glucanase in combination with Xyl-3 improved the AX extraction, but it did not have a marked effect on the viscosity of the extracts. Xyl-3 was then tested on a high-shear-treated rye bran, and results were compared to those obtained with the high-temperature-extruded rye bran. The high-shear treatment did not improve the bran AX enzymatic solubilization. The combination of FAE with Xyl-1 or Xyl-3 did not improve the AX extraction from untreated and high-shear-treated rye bran. Finally, to study the gelation capacity of the enzymatically solubilized AX, the effect of the hydrogen peroxide/horseradish peroxidase (H(2)O(2)/POD) was tested on the Xyl-3 high-temperature-extruded bran extracts. Solubilized AX did not gel in the presence of the oxidizing system. 相似文献
The influence of the addition of metal chelators on oxidative stability was studied in a milk drink and in a mayonnaise system containing highly polyunsaturated lipids. Milk drinks containing 5% (w/w) of specific structured lipid were supplemented with lactoferrin (6-24 muM) and stored at 2 degrees C for up to 9 weeks. Mayonnaise samples with 16% fish oil and 64% rapeseed oil (w/w) were supplemented with either lactoferrin (8-32 muM), phytic acid (16-124 muM), or EDTA (16-64 muM) and were stored at 20 degrees C for up to 4 weeks. The effect of the metal chelators was evaluated by determination of peroxide values, secondary volatile oxidation products, and sensory analysis. Lactoferrin reduced the oxidation when added in concentrations of 12 muM in the milk drink and 8 muM in the mayonnaise, whereas it was a prooxidant at higher concentrations in both systems. In mayonnaise, EDTA was an effective metal chelator even at 16 muM, whereas phytic acid did not exert a distinct protective effect against oxidation. The differences in the equimolar effects of the metal chelators are proposed to be due to differences in their binding constants to iron and their different stabilities toward heat and low pH. 相似文献
Objective: To provide information on the ingestion, and subsequent toxicity, of raw bread dough in dogs. Case summary: A report from the ASPCA animal poison control center (APCC) files of 3 cases of ingestion of raw bread dough by dogs. Clinical signs included vomiting, ataxia, blindness, hypothermia, and recumbency. All dogs were successfully treated for ethanol toxicosis. New information: Ingestion of bread dough can cause gastric obstruction, bloat, or ethanol toxicosis. The treatment of ethanol toxicosis, including decontamination, IV fluids, management of metabolic acidosis, and hypoglycemia is discussed. Yohimbine can be used in cases where the dog is comatose or has developed severe respiratory depression. 相似文献
Of 345 market chicken carcasses received directly from selected processing plants across Canada, six yielded salmonellae. One of the plants submitted 122 carcasses none of which yielded these organisms. A second plant had one Salmonella-contaminated carcass among 20 which were examined. Each of these two plants was subected to detailed bacteriological examinations on four occasions.
In these detailed examinations a total of 175 samples or specimens for culture were taken from a variety of surfaces including vent areas of carcasses, operators' hands, equipment surfaces and from water in tanks of iced birds. Twenty-five (14 per cent) of the cultures yielded salmonellae and all but one of these were either S. oranienburg or S. infantis. Isolations were made during five of the eight series of examinations. The evidence indicated that Salmonella-infected flocks were frequently slaughtered and that Salmonella contamination could become widespread in the plant during processing. The organisms are apparently eliminated from all but a small percentage of the carcasses during processing but opportunities exist for recontamination during subsequent handling.