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101.
102.
A method is described for sensitive and reliable determination of trace concentrations of cadmium, lead and copper in real samples by stripping potentiometry with a home-made flow cell. The selection of the experimental conditions was made using experimental design methodology. The optimum conditions for the method include an acetic acid–acetate buffer mixture (pH 3.4) as supporting electrolyte, an electrolysis potential of −1.1 V and a flow rate of 3 ml min−1. The detection limits were 6.51 × 10−10 mol l−1 for cadmium, 4.60 × 10−10 mol l−1 for lead and 8.59 × 10−10 mol l−1 for copper, with an electrolysis time of 900 s. The relative standard deviations at this concentration level were 0.038, 0.086 and 0.095, respectively. In order to check the analytical accuracy, standard solutions have been used and recoveries close to 100% were obtained. The method was successfully applied to the determination of cadmium, lead and copper in powdered milk, using the method of standard additions. 相似文献
103.
Susana Nieto Argelia Garrido Julio Sanhueza Luis A. Loyola Glauco Morales Federico Leighton Alfonso Valenzuela 《Journal of the American Oil Chemists' Society》1993,70(8):773-778
The antioxidant activities against fish oil oxidation of six commercially available flavonoids and of five flavonoids purified
from two Chilean native plants were compared to those ofdl-α-tocopherol and of two synthetic antioxidants, butylated hydroxytoluene and butylated hydroxyanisole. Among the commercial
flavonoids, catechin, morin and quercetin showed a higher activity when fish oil oxidation (either spontaneous or Fe2+-induced) was assessed from the formation of peroxides or thiobarbituric acid-reactive substances. Among the native flavonoids,
the 5,3′,4′-trihydroxy-7-methoxy flavanone (designated as Pt-2) showed the highest antioxidant activity. Mixtures of quercetin
or of Pt-2 withdl-α-tocopherol produced better inhibitory effects when compared to that of each substance assayed by itself. Also, when Pt-2
and quercetin were assayed in combination (0.3 g/kg oil and 0.7 g/kg oil, respectively), a synergistic antioxidant effect
was observed. Results indicate that several flavonoids could be used as natural antioxidants as a means to replace those synthetic
antioxidants, the use of which has been questioned. 相似文献
104.
Romina Giacometti Florencia Kronberg Ricardo M. Biondi Susana Passeron 《Yeast (Chichester, England)》2009,26(5):273-285
Candida albicans cAMP‐dependent protein kinase (PKA) is coded by two catalytic subunits (TPK1 and TPK2) and one regulatory subunit (BCY1). In this organism the cAMP/PKA signalling pathway mediates basic cellular processes, such as the yeast‐to‐hyphae transition and cell cycle regulation. In the present study, we investigated the role of C. albicans PKA in response to saline, heat and oxidative stresses as well as in glycogen storage. To fine‐tune the analysis, we performed the studies on several C. albicans PKA mutants having heterozygous or homozygous deletions of TPK1 and/or TPK2 in a different BCY1 genetic background. We observed that tpk1Δ/tpk1Δ strains developed a lower tolerance to saline exposure, heat shock and oxidative stress, while wild‐type and tpk2Δ/tpk2Δ mutants were resistant to these stresses, indicating that both isoforms play different roles in the stress response pathway. We also found that regardless of the TPK background, heterozygous and homozygous BCY1 mutants were highly sensitive to heat treatment. Surprisingly, we observed that those strains devoid of one or both TPK1 alleles were defective in glycogen storage, while strains lacking Tpk2 accumulated higher levels of the polysaccharide, indicating that Tpk1 and Tpk2 have opposite roles in carbohydrate metabolism. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
105.
Structural basis of biological nitrogen fixation 总被引:2,自引:0,他引:2
Rees DC Akif Tezcan F Haynes CA Walton MY Andrade S Einsle O Howard JB 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2005,363(1829):971-84; discussion 1035-40
Biological nitrogen fixation is mediated by the nitrogenase enzyme system that catalyses the ATP dependent reduction of atmospheric dinitrogen to ammonia. Nitrogenase consists of two component metalloproteins, the MoFe-protein with the FeMo-cofactor that provides the active site for substrate reduction, and the Fe-protein that couples ATP hydrolysis to electron transfer. An overview of the nitrogenase system is presented that emphasizes the structural organization of the proteins and associated metalloclusters that have the remarkable ability to catalyse nitrogen fixation under ambient conditions. Although the mechanism of ammonia formation by nitrogenase remains enigmatic, mechanistic inferences motivated by recent developments in the areas of nitrogenase biochemistry, spectroscopy, model chemistry and computational studies are discussed within this structural framework. 相似文献
106.
Silva AP Guimarães DE Mizurini DM Maia IC Ortiz-Costa S Sardinha FL do Carmo MG 《Lipids》2006,41(6):535-541
The purpose of this study was to evaluate the effects of four isoenergetic diets of differing fat composition on blood lipid
profile and adiposity in young rats. Diets containing different lipid sources—partially hydrogenated vegetable oil (PHVO),
palm oil (PO), canola oil (CO), and soy oil (SO)—were fed to lactating rats during the 21 days of lactation, and then fed
to young males following weaning until the 45th, day of life. In vivo lipogenesis rate (LR), lipid content (LC), relative level of FA, and the activity of lipoprotein lipase (LPL) enzyme were
measured in epididymal adipose tissue (EPI). Fasting blood lipoproteins and LC in the carcass were also appraised. Body weight
of PO and PHVO groups was significantly higher than CO and SO groups from day 14 of lactation to day 45, despite the lower
food intake in the PHVO group. PO and PHVO groups presented higher LR and LC in EPI than SO and CO groups. Carcass fat content
was significantly higher in PHVO and PO groups than in CO and SO groups. The LPL activity in EPI was unaffected by dietary
lipids. PHVO group had increased total cholesterol and TAG concentrations in comparison with the PO group, and significantly
lower HDL level compared with the other groups. These results show that the kind of FA in the dietary lipid offered early
in life can affect lipid metabolism and adiposity. 相似文献
107.
The effect of polyphenols, phenolic acids and tannins (PPTs) from strawberry and apple on uptake and apical to basolateral transport of glucose was investigated using Caco‐2 intestinal cell monolayers. Substantial inhibition on both uptake and transport was observed by extracts from both strawberry and apple. Using sodium‐containing (glucose transporters SGLT1 and GLUT2 both active) and sodium‐free (only GLUT2 active) conditions, we show that the inhibition of GLUT2 was greater than that of SGLT1. The extracts were analyzed and some of the constituent PPTs were also tested. Quercetin‐3‐O‐rhamnoside (IC50=31 μM), phloridzin (IC50=146 μM), and 5‐caffeoylquinic acid (IC50=2570 μM) contributed 26, 52 and 12%, respectively, to the inhibitory activity of the apple extract, whereas pelargonidin‐3‐O‐glucoside (IC50=802 μM) contributed 26% to the total inhibition by the strawberry extract. For the strawberry extract, the inhibition of transport was non‐competitive based on kinetic analysis, whereas the inhibition of cellular uptake was a mixed‐type inhibition, with changes in both Vmax and apparent Km. The results in this assay show that some PPTs inhibit glucose transport from the intestinal lumen into cells and also the GLUT2‐facilitated exit on the basolateral side. 相似文献
108.
A rapid method for evaluation of the oxidation stability of castor oil FAME: influence of antioxidant type and concentration 总被引:1,自引:0,他引:1
Susana V. Araújo F. Murilo T. Luna Estlio M. Rola Jr. Diana C.S. Azevedo Clio L. Cavalcante Jr. 《Fuel Processing Technology》2009,90(10):1272-1277
The oxidation stability of castor oil fatty methyl ester (FAME), doped with four different phenolic antioxidants, was evaluated using a rapid method of thermal and air-contact degradation. The methodology is based on the induction times observed when the samples are contacted with pure oxygen at elevated pressures and temperatures. The results indicate different performances of the antioxidants as well as synergisms between antioxidants and biodiesel. In general, the addition of antioxidants increased from 6-15 times the stability of castor oil FAME., with BHA (butylated hydroxyanisol) showing the best results for improving antioxidation in castor oil biodiesel. 相似文献
109.
Mendiola JA Santoyo S Cifuentes A Reglero G Ibáñez E Señoráns FJ 《Journal of food protection》2008,71(10):2138-2143
The objective of this research was to evaluate the antimicrobial activity of carbon dioxide extracts of the unicellular biflagellated green alga Dunaliella salina against Escherichia coli, Staphylococcus aureus, Candida albicans, and Aspergillus niger. The effects of different extraction pressures ranging from 185 to 442 bar and extraction temperatures ranging from 9.8 to 45.2 degrees C on the extracts' composition and consequently on their antimicrobial activities were investigated. The extracts were analyzed by gas chromatography-mass spectrometry in order to identify the compounds responsible for the antimicrobial activity detected. Fourteen different volatile compounds and several fatty acids were identified. The highest antimicrobial activity was obtained using 314 bar and 9.8 degrees C. Under these conditions, the presence of an indolic derivative that had never been reported in D. salina was detected in the extract, together with polyunsaturated fatty acids and compounds related to carotene metabolism, such as beta-ionone and neophytadiene, with known antimicrobial activity. 相似文献
110.
Susana M Cardoso Isabel Mafra Ana Reis Dominique MR Georget Andrew C Smith Keith W Waldron Manuel A Coimbra 《Journal of the science of food and agriculture》2008,88(12):2079-2086
BACKGROUND: Thasos is an olive variety cultivated mainly in Greece used to produce ‘naturally black dry‐salted olives’. This process consists in placing the olives in disposed layers with coarse sodium chloride. The loss of water and other solutes gradually debitters and wrinkles the fruits. In this study, the effect of dry‐salt processing on the texture and cell wall polysaccharide composition was investigated. RESULTS: This type of processing affected primarily the mechanical properties of the olive flesh. In processed olives, this tissue was approximately 4.5 times stronger and also more deformable up to failure and stiffer than that from the raw olives. The dry‐salt processing had its strongest effect on pectic polysaccharides. This included the increment of solubilization of arabinose‐rich polymers in aqueous solutions, and thus their partial loss to the soak medium during dry‐salting. Contrarily, galacturonic acid‐rich polymers were further retained in the processed olives, probably by their stabilization within the cell walls by reduction of the electrostatic repulsion between the acidic groups of these polysaccharides due to sodium ions. CONCLUSION: The texture improvement of olive flesh by dry‐salt processing seems to be correlated with the reorganization of the galacturonic acid‐rich pectic polysaccharides into the cell wall of the fruit. Copyright © 2008 Society of Chemical Industry 相似文献