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51.
J. S. Felton Pilar Pais Cynthia P. Salmon Mark G. Knize 《European Food Research and Technology》1998,207(6):434-440
Levels of known heterocyclic amines vary from undetectable in many meats sold in fast food restaurants, to over 10 ng/g for
meats prepared in restaurants that cook food to order, to hundreds of nanograms per gram for some meats cooked under certain
home or laboratory conditions. To simulate the dry reactions that seem to occur at the meat surface we developed a model system
to mimic these processes. Mixtures of free amino acids, creatinine and glucose, simulating the composition of beef or chicken,
heated at 200 °C, form eight heterocyclic amines. Besides the commonly found 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3-methylimidazo[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, 2-amino-1,6-dimethylimidazo[4,5-b]pyridine, 2-amino-1,5,6-trimethylimidazo[4,5-b]pyridine and 2-amino-1,6-dimethylfuro[3,2-e]imidazo[4,5-b]pyridine were also found. The calculated risk of consumption of heterocyclic amines is determined by the dietary dose, the
extrapolation of carcinogenic potencies from rodents to humans, and the extrapolation of high rodent doses to low human exposures.
Results suggest that DNA binding is linear with dose, but that the human DNA forms more adducts per unit dose than that of
the rat. Altogether, the risk appears to be equivalent to that for many carcinogens that are regulated.
Received: 23 April 1998 相似文献
52.
Silva AR Paulo EN Sant'Ana AS Chaves RD Massaguer PR 《International journal of food microbiology》2011,148(3):156-163
The objectives of this study were to isolate psychrotrophic clostridia from Brazilian vacuum-packed beef cuts (spoiled or not) and to identify the isolates by using 16S rRNA gene sequencing. Anaerobic psychrotrophic microorganisms were also enumerated and samples were collected to verify the incidence of psychrotrophic clostridia in the abattoir environment. Vacuum-packed beef cuts (n = 8 grossly distended and n = 5 non-spoiled) and environmental samples were obtained from a beef packing plant located in the state of São Paulo, Brazil. Each sample was divided in three subsamples (exudate, beef surface and beef core) that were analyzed for vegetative forms, total spore-forming, and sulfide reducing spore-forming, both activated by alcohol and heat. Biochemical profiles of the isolates were obtained using API20A, with further identification using 16S rRNA gene sequencing. The growth temperature and the pH range were also assessed. Populations of psychrotrophic anaerobic vegetative microorganisms of up to 1010 CFU/(g, mL or 100 cm2) were found in ‘blown pack’ samples, while in non-spoiled samples populations of 105 CFU/(g, CFU/mL or CFU/100cm2) was found. Overall, a higher population of total spores and sulfide reducing spores activated by heat in spoiled samples was found. Clostridium gasigenes (n = 10) and C. algidicarnis (n = 2) were identified using 16S rRNA gene sequencing. Among the ten C. gasigenes isolates, six were from spoiled samples (C1, C2 and C9), two were isolated from non-spoiled samples (C4 and C5) and two were isolated from the hide and the abattoir corridor/beef cut conveyor belt. C. algidicarnis was recovered from spoiled beef packs (C2). Although some samples (C3, C7, C10 and C14) presented signs of ‘blown pack’ spoilage, Clostridium was not recovered. C. algidicarnis (n = 1) and C. gasigenes (n = 9) isolates have shown a psychrotrophic behavior, grew in the range 6.2-8.2. This is the first report on the isolation of psychrotrophic Clostridium (C. gasigenes and C. algidicarnis) in Brazil. This study shows that psychrotrophic Clostridium may pose a risk for the stability of vacuum-packed beef produced in tropical countries during shelf-life and highlights the need of adopting control measures to reduce their incidence in abattoir and the occurrence of ‘blown pack’ spoilage. 相似文献
53.
Carmen Gómez-Guillen Teresa Solas Javier Borderías Pilar Montero 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,202(3):221-227
This paper seeks to compare the ultrastructure of gels made from frozen muscle of giant squid (Dosidicus gigas) at various temperatures with a number of different rheological parameters, with reference to a variety of added ingredients (non-muscle proteins and hydrocolloids) and to NaCl concentration. Interesting data on gel rheological properties were found where formulae containedl-carrageenan, starch and egg white, with a low salt concentration (1.5%). This seems to be because carrageenan forms an independent network which supports the principal structure formed by the fish protein; starch is incorporated into the network and retains water; and egg white forms a supplementary network which helps to improve rheological properties. 相似文献
54.
Gustavo Larsen Edgar Lotero Rubn D. Parra Lucía M. Petkovic Hugo S. Silva Srinivasanallur Raghavan 《Applied Catalysis A: General》1995,130(2):213-226
Palladium supported on sulfated zirconia (PdSZ) has been characterized by the n-butane isomerization reaction in the presence of hydrogen, X-ray absorption spectroscopy (XAS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) of adsorbed carbon monoxide. Catalyst calcination at 873 K followed by hydrogen reduction at 513 K results in the formation of 30–40 Å Pd metal clusters, but the surface can only weakly adsorb CO, though stronger than Pd-free, sulfated zirconia catalysts. In the presence of hydrogen, PdSZ has a lower n-butane isomerization activity than SZ, and the Pd function cannot stabilize the reaction at low H2/n-butane ratios. 相似文献
55.
Sarah Laraichi Pilar Parra Rocío Zamanillo Ahmed El Amarti Andreu Palou Francisca Serra 《Lipids》2013,48(8):817-826
The scope of this study was to assess the impact of calcium and conjugated linoleic acid (CLA) supplementation on plasma fatty acid profiles and to evaluate potential synergistic effects of both compounds against dietary obesity. Mice separated into five experimental groups were followed: control (C), high-fat diet (HF), HF with calcium (Ca), HF plus CLA and HF with both Ca and CLA. Plasma metabolites and fatty acids were determined by commercial kits and gas chromatography, respectively. Both dietary calcium and CLA supplementation contributed to lower body fat gain under a HF diet. Maximum efficacy was seen with calcium; no additional effect was associated with the combined treatment with CLA. Plasma leptin, adiponectin and HOMA index were in accordance with an altered glucose/insulin homeostasis in the HF and HF + CLA groups, whereas control levels were attained under Ca-enriched diets. Plasma fatty acids showed minor changes associated to CLA treatment, but a high impact on PUFA was observed under Ca-enriched diets. Our results show that the mechanism underlying the anti-obesity effects of calcium supplementation is mediated mainly by changes in PUFA plasma profile. In addition, the lack of synergy on body weight reduction in combination with associated lipid profiles of calcium and CLA suggests that calcium may interfere with absorption and/or bioactivity of CLA, which can be of relevance when using CLA-fortified dairy products against human obesity. 相似文献
56.
A study was carried out to increase the CLA contents in ewes’ milk fat under field conditions by dietary means and to investigate
the extent of the changes and consequences for milk processing and cheese quality. During a 3-mon period, ewes’ bulk milk
samples were collected every week from two different herds. For the first 4 wk the ewes were fed a conventional diet. Then
the following 6 wk a supplement enriched in α-linolenate (whole linseed) was incorporated into the ovine diet. Finally, in
the last 3 wk the feeding was the same as in the first 4 wk. The FA profile in milk fat was monitored by GC, and the distribution
of CLA isomers was thoroughly tested by combining GC-MS of 4,4-dimethyloxazoline derivatives (DMOX) with silver ion-HPLC (Ag+-HPLC) of FAME. Reconstructed mass spectral profiles of CLA characteristic ions from DMOX were used to identify positional
isomers, and Ag+-HPLC was used to quantify them. An increase in total CLA in milk fat was observed, and total CLA remained elevated during
the weeks of enriched α-linolenate feeding. In our experimental conditions there was a linear relationship between trans-vaccenic acid (trans-11-octadecenoic acid; trans-11 18∶1) and 9-cis, 11-trans CLA in ewes’ milk fat. Concerning the CLA isomer profile, increases in the 11,13- and 12,14–18∶2 positional isomers were
considerable when linseed was included in the diet. Organoleptic characteristics of cheeses made with CLA-enriched milk did
not substantially differ from those made with nonsupplemented ewes’ milk. CLA total content and isomer profile did not change
during ripening. 相似文献
57.
Ignacio Contreras Andrade ;Jonathan Parra Santiago ;Jose Ricardo Sodre ;Joseph Sebastian Pathiyamattom ;Carlos Alberto Guerrero-Fajardo 《化学与化工:英文版》2014,(7):717-726
Currently, biodiesel is presented as one of the best alternatives for gradually replacing the use of fossil fuels, but it has some factors that make it economically impractical if it does not have a government support. For this reason, research efforts focused on this area have been responsible for optimizing the process of biodiesel production by different catalytic routes to achieve greater efficiency at a lower cost. In this case, the biggest problem has been the high cost generated by an investigation, which in many occasions is the main factor to decide if an investigation could be carried out. Trying to reduce these costs, in the current study, we are using a technique of glycerol quantification by volumetric methods and comparing obtained results with the chromatographic method, which is conventionally used and comparatively much more expensive. Biodiesel employee was obtained by an enzymatic catalysis process varying one of three process variables:oil:alcohol molar ratio, temperature and proportion of catalyst. The numerical differences obtained between the two quantification methods generated relative errors lower than 10%, resulting in some occasions lower than 1%. By gas chromatography analysis the best yield was obtained at the same conditions of the volumetric method, a temperature of 45 ℃, an oil:alcohol ratio 1:4 and 8 wt.% of catalyst, but a yield of 95.5% and 97.1%, respectively. Due to the high precision of gas chromatography, this method is used to carry out a surface response analysis obtaining as ideal operating conditions a temperature of 43.5 ℃, 8.9 wt.%. of catalyst and an oil:alcohol ratio 1:4. 相似文献
58.
Polythene films coated with the enterococcal bacteriocin enterocin EJ97 alone or in combination with EDTA were tested against Bacillus coagulans CECT 12. Bacteriocin activity was clearly enhanced by EDTA, as shown by viable staining and epifluorescence microscopy observation of treated cells. Activated films were tested in liquids from canned corn and canned peas inoculated with B. coagulans cell suspensions and stored at 4 °C and 20 °C for 24 h. The bacteriocin alone showed highest activity in samples stored at 4 °C, while the maximum performance of EDTA was observed at 20 °C. Films activated with a combination of both antimicrobials showed highest bactericidal activity at 4 °C. In liquid from canned corn and peas stored at 4 °C, the combined treatment reduced the concentrations of viable cells progressively over incubation time. Viable staining revealed an increase in the percentage of dead cells at 20 °C, avoiding proliferation of the bacilli. The bactericidal effect of the combined antimicrobial agents was higher in the liquid of canned peas than that of canned corn. The combined use of viable staining and classical viable cell counts allowed a better estimation of cell damage caused by the antimicrobial treatments. 相似文献
59.
I. Wilkomirsky R. Parra F. Parada E. Balladares 《JOM Journal of the Minerals, Metals and Materials Society》2014,66(9):1687-1693
Continuous converting of copper matte or white metal into blister copper is carried out in a new, high-intensity falling film type of molten-layer reactor that operates with dry, high-grade matte or white metal ground to ?65 mesh and technical oxygen. The reactor operates at up to 1500°C to 1600°C producing a blister copper with 0.5–0.8% S, which can be refined in a conventional manner, and a slag containing less than 8% Cu. The reactor is designed to operate continuously producing an off-gas containing over 50% SO2. The developed phenomenological model of the molten-layer reactor was found to predict with good agreement the results obtained in a one-tonne-per-day pilot reactor. 相似文献
60.
Raúl Vicen-Bueno M. Pilar Jarabo-Amores Manuel Rosa-Zurera José L. Sanz-González Saturnino Maldonado-Bascón 《Neural Processing Letters》2010,32(3):249-268
To train Neural Networks (NNs) in a supervised way, estimations of an objective function must be carried out. The value of
this function decreases as the training progresses and so, the number of test observations necessary for an accurate estimation
has to be increased. Consequently, the training computational cost is unaffordable for very low objective function value estimations,
and the use of Importance Sampling (IS) techniques becomes convenient. The study of three different objective functions is
considered, which implies the proposal of estimators of the objective function using IS techniques: the Mean-Square error,
the Cross Entropy error and the Misclassification error criteria. The values of these functions are estimated by IS techniques,
and the results are used to train NNs by the application of Genetic Algorithms. Results for a binary detection in Gaussian
noise are provided. These results show the evolution of the parameters during the training and the performances of the proposed
detectors in terms of error probability and Receiver Operating Characteristics curves. At the end of the study, the obtained
results justify the convenience of using IS in the training. 相似文献