Mechanisms of solute transport affect small-scale abundance and function of soil microorganisms in the detritusphere   总被引：2，自引：0，他引：2  

C. Poll  J. Ingwersen  M. Stemmer  M. H. Gerzabek  & E. Kandeler 《European Journal of Soil Science》2006,57(4):583-595

In the detritusphere, particulate organic matter offers new sites for microorganisms, whereas soluble substrates are transported into the adjacent soil. We investigated how mechanisms of solute transport affect microbial abundance and function in the detritusphere. In a first experiment, transport was restricted to diffusion, whereas in a second experiment it was dominated by convection. Two soil moisture contents were established in each experiment. When diffusion was the exclusive transport mechanism, the addition of maize litter induced distinct gradients in enzyme activities, soil organic C content and microbial biomass to a depth of 1.5–2.8 mm. Convection enlarged these gradients to 2.5–3.0 mm. The moisture regime modified the temporal pattern of diffusive C transport, microbial growth and enzyme release by inducing faster transport at large water contents. Convective transport seemed to be unaffected by soil moisture content. Using a convective‐diffusive transport model with first‐order decay, it was possible to simulate the observed activity profiles. The results indicate that the spatial dimension of the detritusphere is governed by the ratio between decay rate of available substrates and transport rate. Bacteria and fungi showed differing utilization strategies as revealed by coupling phospholipid fatty acid (PLFA) analysis with stable isotope techniques. Fungi assimilated C directly in the litter, whereas bacteria took up the substrates in the soil and therefore depended more on transport processes than fungi. Our results demonstrate the impact of physicochemical conditions on the abundance and function of microorganisms in the detritusphere. Furthermore, the combination of enzymatic measurements and mathematical transport modelling may offer a new way to measure substrate decay rates in soil.  相似文献   

Antioxidant synergy and regeneration effect of quercetin, (-)-epicatechin,and (+)-catechin on alpha-tocopherol in homogeneous solutions of peroxidating methyl linoleate     

Pedrielli P  Skibsted LH 《Journal of agricultural and food chemistry》2002,50(24):7138-7144

Antioxidant interactions between flavonoids and alpha-tocopherol have been demonstrated by oximetry (oxygen concentration measured by ESR signal line width). In tert-butyl alcohol, a solvent in which flavonoids are weak retarders of peroxidation of methyl linoleate when initiated by alpha,alpha'-azoisobutyronitrile, quercetin and (-)-epicatechin were found to act synergistically with the chain-breaking antioxidant alpha-tocopherol. In chlorobenzene, a solvent in which flavonoids are chain-breaking antioxidants, quercetin and (+)-catechin each regenerated alpha-tocopherol, resulting in a co-antioxidant effect. The stoichiometric factor of the flavonoids as chain-breaking antioxidants in 1:1 mixtures with alpha-tocopherol was measured to be close to 1 for quercetin and slightly smaller for the catechins. The apparent inhibition rate constant, k(inh), for the mixture quercetin/alpha-tocopherol was measured to be 4.1 x 10(5) and 2.6 x 10(6) M(-1) s(-1) in tert-butyl alcohol and chlorobenzene, respectively, at 50 degrees C. A k(inh) of 4.4 x 10(5) M(-1) s(-1) was measured for (+)-catechin alone in chlorobenzene at 50 degrees C.  相似文献   

Comment on "Does the hydrated electron occupy a cavity?"     

Jacobson LD  Herbert JM 《Science (New York, N.Y.)》2011,331(6023):1387; author reply 1387

Larsen et al. (Reports, 2 July 2010, p. 65) challenged the long-standing model of the solvent geometry surrounding a free electron in water using molecular dynamics simulations based on a newly derived electron-water pseudopotential. We illustrate that, in contrast to the model they used, the true electron-water interaction is repulsive in the region relevant to the reported extended electron distribution, consistent with the cavity model.  相似文献   

Protein,amino acids and some major and trace elements in Thai and Norwegian mushrooms     

Piyawan Surinrut  Kåre Julshamn  Leif Rein Njaa 《Plant foods for human nutrition (Dordrecht, Netherlands)》1987,37(2):117-125

Six edible Thai mushroom species were analysed for protein, in vitro protein digestibility, amino acids and major and trace elements. The results for protein and amino acids were discussed relative to the contents in Thai rice. The contents of mineral elements showed great variation, in agreement with literature data. Two samples (Hunukao and Hom) were rich in calcium and one (Phang) was rich in iron and copper. For comparison results for samples of edible mushrooms obtained in Norway were included.  相似文献   

Effect of a Bangladeshi home-cooking procedure on the amino acid content,trypsin inhibitor activity and in vitro digestibility of some legume seeds     

Sultana Sayeed  Leif R Njaa 《Plant foods for human nutrition (Dordrecht, Netherlands)》1985,35(4):379-388

Raw and cooked samples of cultivars ofLens esculenta (Lentils),Pisum sativum (peas),Phaseolus vulgaris (beans),Phaseolus aureus (navy beans)Cicer arietnum (gram), andLathyrus sativus (dhal) as well as precooked commercial products were analysed for amino acids, trypsin inhibitor activity and in vitro protein digestibility. Of the fifteen samples used in the study one lentil sample, one pea sample, two gram samples and one sample of khesari dhal were from Bangladesh, one gram sample was from Sri Lanka. The other samples were obtained either in shops in Norway or from an industrial firm. The latter were also obtained precooked and dried. The two samples obtained in shops were used with hull and dehulled.Neither cooking by a Bangladeshi household procedure nor industrial precooking and drying had any effect on the amino acid contents of the samples.Cooking and precooking reduced the trypsin inhibitor activity of the raw samples more when the original activity was high then when it was low. The inhibitor activity was similar between samples after cooking.Cooking and precooking and drying increased the in vitro protein digestibility in all samples except in the lentils in which the digestibility was reduced.In the raw samples protein digestibility was negatively correlated with the trypsin inhibitor activity.  相似文献   

Changes in flavor-affecting aroma compounds during potato storage are not associated with lipoxygenase activity     

Mikael Agerlin Petersen  Leif Poll  Lone Melchior Larsen 《American Journal of Potato Research》2003,80(6):397-402

When potatoes are boiled and then chill-stored they rapidly develop off-flavor. This is a result of lipoxygenase activity, and is a serious problem in food-service systems. Lipoxygenase activity may vary during winterstorage of potatoes. Raw potatoes of the variety ‘Bintje’ were therefore analyzed for lipoxygenase activity during winter storage. Furthermore, content of potential offflavors and typical potato aroma compounds were determined in raw, boiled, and in boiled/chill-stored potatoes. Four months after harvest the lipoxygenase activity started to increase, both when linoleic and linolenic acid were used as substrates. Production of typical oxidation products (aldehydes) of these fatty acids that earlier have been shown to cause off-flavor in boiled/chillstored potatoes did, however, decrease. It is therefore concluded that this was not due to changes in lipoxygenase activity  相似文献   

Wavelength dependence of light-induced lipid oxidation and naturally occurring photosensitizers in cheese     

Andersen CM  Andersen LT  Hansen AM  Skibsted LH  Petersen MA 《Journal of agricultural and food chemistry》2008,56(5):1611-1618

Degradation of the potential photosensitizers, riboflavin, chlorophyll, and porphyrin, in Danbo cheese by monochromatic light of wavelength 366, 436, or 546 nm was studied. Three cheeses were investigated, two conventional (16% fat and 25% fat) and one "organic" (25% fat). The effect of illumination was measured by fluorescence spectroscopy and analyzed using multiway and multivariate data analysis. Riboflavin was found to degrade only by 436 nm light, whereas chlorophylls and porphyrins also were influenced by 436 and 546 nm light. The organic cheese had the largest chlorophyll content both before and after similar light exposure, and no change in chlorophyll of this cheese was observed for any of the illumination wavelengths. Upon light exposure of the cheeses, volatile compounds were formed, as analyzed by gas chromatography-mass spectrometry (GC-MS). The relative concentrations of methyl butanoate, 1-pentanol, benzaldehyde, 2-butanone, 2-heptanone, and butyl acetate were found to weakly correlate with the surface fluorescence intensity. 1-Pentanol and the ketones are secondary lipid oxidation products, consistent with a chemical coupling between photosensitizer degradation and formation of volatile lipid oxidation products.  相似文献   

Interactions between iron, phenolic compounds, emulsifiers, and pH in omega-3-enriched oil-in-water emulsions   总被引：1，自引：0，他引：1  

Sørensen AD  Haahr AM  Becker EM  Skibsted LH  Bergenståhl B  Nilsson L  Jacobsen C 《Journal of agricultural and food chemistry》2008,56(5):1740-1750

The behavior of antioxidants in emulsions is influenced by several factors such as pH and emulsifier type. This study aimed to evaluate the interaction between selected food emulsifiers, phenolic compounds, iron, and pH and their effect on the oxidative stability of n-3 polyunsaturated lipids in a 10% oil-in-water emulsion. The emulsifiers tested were Tween 80 and Citrem, and the phenolic compounds were naringenin, rutin, caffeic acid, and coumaric acid. Lipid oxidation was evaluated at all levels, that is, formation of radicals (ESR), hydroperoxides (PV), and secondary volatile oxidation products. When iron was present, the pH was crucial for the formation of lipid oxidation products. At pH 3 some phenolic compounds, especially caffeic acid, reduced Fe(3+) to Fe(2+), and Fe(2+) increased lipid oxidation at this pH compared to pH 6. Among the evaluated phenols, caffeic acid had the most significant effects, as caffeic acid was found to be prooxidative irrespective of pH, emulsifier type, and presence of iron, although the degrees of lipid oxidation were different at the different experimental conditions. The other evaluated phenols were prooxidative at pH 3 in Citrem-stabilized emulsions and had no significant effect at pH 6 in Citrem- or Tween-stabilized emulsions on the basis of the formation of volatiles. The results indicated that phenol-iron complexes/nanoparticles were formed at pH 6.  相似文献   

Heme-mediated production of free radicals via preformed lipid hydroperoxide fragmentation     

Pazos M  Andersen ML  Skibsted LH 《Journal of agricultural and food chemistry》2008,56(23):11478-11484

Electron spin resonance (ESR) spectroscopy and the spin-trapping technique were used to investigate the capacity of several hemoglobin (Hb) forms of rainbow trout (oxyHb and metHb), free hemin (oxidized form of heme group), and hemin complexed with bovine serum albumin (BSA) to promote formation of free radicals via fragmentation of preformed lipid hydroperoxides. Cumene hydroperoxide (CumOOH) was used as a model for lipid hydroperoxide, and free radicals were monitored by stabilizing with the spin traps alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Two different types of free radicals, hydroxyl and carbon-centered radicals, were identified as a result of the interaction of the heme-containing systems and CumOOH. Carbon-centered radicals were found to be mainly heme-mediated because the addition of the iron-chelating agent EDTA did not affect the formation of POBN/carbon-centered adducts. Hemin alone was the best promoter for the production of POBN/carbon-centered radicals in the presence of low hydroperoxide concentrations (below equimolar condition over heme group), whereas hemin/BSA and oxyHb were more active in generating radicals at high hydroperoxide concentrations or after successive interactions with hydroperoxides. This finding can be explained by the coexistence of two different facts: (i) the interaction between hemin and lipid hydroperoxides seems to be more efficient in the case of free hemin compared to heme-protein complexes and (ii) a faster degradation of hemin is produced without the presence of a protein fraction, globin or albumin. The comparison of oxyHb and metHb also suggested that both Hb redox states have similar capacities to generate oxidative stress via cleavage of preformed lipid hydroperoxides.  相似文献   

Characterizing larval swordfish habitat in the western tropical North Atlantic          下载免费PDF全文

Justin J. Suca  Leif K. Rasmuson  Estrella Malca  Trika Gerard  John T. Lamkin 《Fisheries Oceanography》2018,27(3):246-258

Swordfish Xiphias gladius (Linnaeus, 1758) are a circumglobal pelagic fish targeted by multiple lucrative fisheries. Determining the distribution of swordfish larvae is important for indicating reproductive activity and understanding the early life history of swordfish. We identify and characterize larval swordfish distributions during peak swordfish spawning throughout the Gulf of Mexico and western Caribbean Sea with generalized additive models (GAMs) using catches of swordfish larvae during ichthyoplankton surveys in April and May of 2010, 2011, and 2012. The best fit GAM, as determined by stepwise, backward Akaike Information Criterion selection, included both physiochemical (temperature at 5 m, sea surface height anomaly (SSHA), eddy kinetic energy (EKE)), temporal (lunar illumination, hour of sampling) and spatial (location) variables, while near surface chlorophyll a concentration residuals remained as a random effect. The highest probability of larval swordfish catch occurred at sub‐surface temperatures, SSHA, and EKE values indicative of boundary currents. Standard lengths of larvae were larger further downstream in the boundary currents, despite high variability in length with location due to multiple spawning locations of swordfish near these currents. Probability of larval swordfish catch also peaked during the crescent and gibbous moons, indicating a lunar periodicity to swordfish spawning. These results suggest that swordfish may spawn during select moon phases near boundary currents that transport their larvae to larval and juvenile habitat including the northern Gulf of Mexico and coastal waters of the southeast United States.  相似文献