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排序方式: 共有3210条查询结果,搜索用时 31 毫秒
941.
Lübke M Guichard E Tromelin A Le Quéré JL 《Journal of agricultural and food chemistry》2002,50(24):7094-7099
Interactions between a well-characterized protein, beta-lactoglobulin, and two flavor compounds, beta-ionone and gamma-decalactone, were studied by 2D NMR spectroscopy. NMR spectra were recorded in aqueous solution (pH 2.0, 12 mM NaCl, 10% D(2)O) under conditions such that beta-lactoglobulin is present in a monomeric state. TOCSY and NOESY spectra were recorded on the protein and the complexes between protein and ligands. The spectra of the NH-CH(alpha) region showed the cross-signals due to the coupling between N- and C-bonded protons in the polypeptide backbone. The observed chemical shift variations in the presence of ligands can be assigned to changes in the protein conformation. It appears that the side chains of several amino acids are affected by binding of gamma-decalactone point into the central cavity (Leu46, Ile56, Met107, and Gln120), whereas binding of beta-ionone affects amino acids located in a groove near the outer surface of the protein (Leu104, Tyr120, and Asp129), as illustrated by molecular visualization. This NMR study provides precise information of the location of binding and confirms the existence of two different binding sites for aroma compounds on beta-lactoglobulin, which was suggested in previous competition studies by fluorometry or affinity chromatography and by structural information obtained from infrared spectroscopy. 相似文献
942.
A Geahchan I Le Gren P Chambon R Chambon 《Journal of the Association of Official Analytical Chemists》1991,74(6):968-973
An improved method has been developed for quantitative determination of polynuclear aromatic hydrocarbons (PAHs) in pharmacopoeial paraffin and medicinal white oil samples. This new method combines 2 liquid-liquid partition and adsorption chromatography procedures with a 2-step purification on Sephadex LH 20 and liquid chromatography with fluorometric determination. Selective elution of PAHs results in absence of background fluorescence. The minimum detectable level ranges from 0.2 ppt for benzofluoranthene isomers to 200 ppt for acenaphthene. Recoveries of PAHs added at 7 ppm varied from 92.1 to 111.4%. When a variety of medicinal white oil samples were analyzed by this improved method, 27 PAHs were identified, including 11 suspected carcinogens. Their identities were confirmed by capillary gas chromatography. 相似文献
943.
Inhibition of apple polyphenol oxidase activity by procyanidins and polyphenol oxidation products 总被引:4,自引:0,他引:4
Le Bourvellec C Le Quéré JM Sanoner P Drilleau JF Guyot S 《Journal of agricultural and food chemistry》2004,52(1):122-130
The rate of consumption of dissolved oxygen by apple polyphenol oxidase in cider apple juices did not correlate with polyphenol oxidase activity in the fruits and decreased faster than could be explained by the decrease of its polyphenolic substrates. The kinetics parameters of a crude polyphenol oxidase extract, prepared from apple (Braeburn cultivar), were determined using caffeoylquinic acid as a substrate. Three apple procyanidin fractions of n 80, 10.5, and 4 were purified from the parenchyma of cider apples of various cultivars. Procyanidins, caffeoylquinic acid, (-)-epicatechin, and a mixture of caffeoylquinic acid and (-)-epicatechin were oxidized by reaction with caffeoylquinic acid o-quinone in order to form oxidation products. All the fractions were evaluated for their inhibitory effect on PPO activity. Native procyanidins inhibited polyphenol oxidase activity, the inhibition intensity increasing with n. The polyphenol oxidase activity decreased by 50% for 0.026 g/L of the fraction of n 80, 0.17 g/L of the fraction of n 10.5, and 1 g/L of the fraction of n 4. The inhibitory effect of oxidized procyanidins was twice that of native procyanidins. Oxidation products of caffeoylquinic acid and (-)-epicatechin also inhibited polyphenol oxidase. 相似文献
944.
Le Gall G Colquhoun IJ Davis AL Collins GJ Verhoeyen ME 《Journal of agricultural and food chemistry》2003,51(9):2447-2456
945.
Edith?Le?CadreEmail author Sophie?Génermont Farooq?Azam Sylvie?Recous 《Biology and Fertility of Soils》2004,40(3):178-180
After dissolution of fertiliser granules, a high nitrogen concentration is recovered in the immediate vicinity of granules, which may enhance damaging processes like nitrite accumulation or ammonia volatilisation. Based on the diffusion equations of Cranck, the granule-soil microsite was modelled to obtain the actual fertilised surface plot and the effective rate of N application on this surface. Parameterisation of the diffusion coefficient of solutes consisted of a temperature and soil texture correction. The model was tested against an experimental data set obtained from soil incubations at two soil water contents (21.2% m3 m–3 and 28.3% m3 m–3) and two temperatures (4°C and 25°C) by comparing NH4+ recovery at various distances from the granules. The simulated radius of the granule-soil microsite was more affected by the water content than by the temperature. The model is very accurate because 95–100% of total NH4+ applied was recovered in the modelled surface depending on the experimental conditions (temperature and water content). The model was simple enough to be easily integrated into larger models dealing with surface-applied granule fertilisers. 相似文献
946.
The occurrence of friabilins in triticale and their relationship with grain hardness and baking quality 总被引:3,自引:0,他引:3
Ramírez A Pérez GT Ribotta PD León AE 《Journal of agricultural and food chemistry》2003,51(24):7176-7181
Grain hardness is a quality parameter in wheat and other cereals. In wheat, a group of M(r) 15 000 proteins called friabilins have been shown to be related to grain hardness. The objective of this study was to determine the presence of friabilins on starch granules of different triticale lines and their relationship with grain texture and baking quality. The triticale lines studied have a wide range of hardness, which presented correlation with baking quality parameters such as damaged starch and solvent retention capacity. All of the triticale lines contained friabilins on the starch granules. However, the correlation between hardness and friabilin content was not observed, suggesting that these proteins would not be directly involved in grain texture determination of triticale. Consequently, friabilin content did not have any relation with cookie quality in triticale flours, but it could be related to breadmaking quality because it has a positive correlation with the sodium dodecyl sulfate sedimentation index. 相似文献
947.
Amounts of phosphorus taken up by maize plants during 23 days from an Entisol, two Alfisols and an Ultisol from Nigeria, each with three histories of management, were related to the concentration of soil phosphorus extracted in 0.01 m CaCl2; but the relationships differed between kinds of management. Phosphorus in plants 51 days old was not related to concentration. Relationships of plant phosphorus with isotopically exchangeable phosphorus, and with phosphorus extracted from the soils by anion exchange resin, were poor in young plants but were good in the older plants, irrespective of field management. Amounts of phosphorus in the older plants were also well related to estimates of exchangeable phosphorus computed from P in solution and amounts of amorphous iron oxides extracted by ammonium oxalate from the soils, using equations derived in an earlier investigation with a larger group of soils. Thus estimates of exchangeable phosphorus made from simple measurements of the soil constituents that largely control it, and from extraction by resins, are potentially useful to indicate the ability of soils to supply phosphate to crops, and hence to guide fertilizer policies. 相似文献
948.
In this paper,six reinforced concrete beams dismounted from their worksites under long-term sulphate attack are studied.The authors analyzed the working properties and cracking moment of the reinforced concrete beams under long-term sulphate attack,suggesting that the reinforced concrete beams under long-term sulphate attack may have more favorable cracking-resistant behavior in some circumstances. 相似文献
949.
Genetic modification from selfed progenies of 18 rice (Oryza sativa L.) plants regenerated from callus tissues which survived desiccation, were investigated at the DNA level using the random
amplified polymorphic DNA (RAPD) method. Twelve 10-mer random primers were used to amplify DNA of progenies from the regenerated
plants, and a total of 228 PCR products and 1780 DNA fragments were obtained by primers, generating between four to thirteen
major bands. The size of the amplified fragments ranged from 0.2 to 2.55 kb. The results showed that 10 out of 12 primers
produced polymorphic bands, two primers (RA31 and RA185) showed no polymorphism among plants tested. A dendrogram of the genetic
distance was constructed based on their polymorphism, demonstrating that somaclonal variation exists in rice plants regenerated
from callus which survived the desiccation treatment. Part of this variation can be useful in rice breeding.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
950.
Summary The content of coumarins, as probable phytoalexins, was analysed in four sunflower genotypes that ranged in responses to head
rot from highly susceptible to highly resistant. Low levels of all coumarins (scopolin, scopoletin and ayapin) were detected
in the three most susceptible genotypes irrespective of time after inoculation. However, in the resistant genotype there was
a clear time-dependent disease-induced increase of all coumarins that reached a maximum after 10–14 days. Detailed comparison
of the most susceptible and the resistant genotype showed that in the resistant but not the susceptible, scopoletin peroxidase
activity increased during the course of the experiment. Results confirmed a clear negative correlation between coumarin content
and disease symptoms and in particular for scopolin. Furthermore we show for the first time that scopolin is inhibitory to
Sclerotinia at similar doses to scopoletin. As scopolin is known to be less phytotoxic than ayapin and scopoletin, its accumulation may
well confer head rot resistance with minimal plant damage and might be one of the bases for resistance to Sclerotinia. 相似文献