362 research outputs found
FLOW-THROUGH ANALYSIS OF GLUTATHIONE IN HUMAN ERYTHROCYTES WITH AN AMPEROMETRIC BIOSENSOR
No full textA flow-through system for the determination of glutathione was developed using the enzyme glutathione oxidase covalently immobilized on an Immobilon AV membrane assembled on a Clark type oxygen electrode. A calibration curve for glutathione, was obtained in the range 10(-5) - 10(-3) mol/L with a detection limit of 5 . 10(-6) mol/L and a relative standard deviation of 4.5%.[...
CYCLIC ENZYMATIC DETERMINATION OF L-LACTATE BY DIFFERENTIAL PH MEASUREMENT
No full textAn electrochemical procedure for the analysis of L-lactate based on the lactate dehydrogenase/lactate oxidase reaction cycle has been developed and applied in whole blood and wine. The reaction of lactate with lactate oxidase produces pyruvate, which is the substrate, at physiological pH, of the enzyme lactate dehydrogenase. This enzyme, in the presence of NADH, converts pyruvate to lactate consuming H+ An automated software controlled differential pHmeter was used for H+ detection and the Delta pH measured was correlated to the lactate concentration present in the sample. Lactate was measured in the range 0.4-20 mmol/L with a detection limit of 0.2 mmol/L. Recovery studies have been carried out to evaluate the effect of blood and wine matrices on lactate determination. The recovery was between 94 and 104% in blood and 93 and 104% in wine. Analysis of lactate in blood and wine samples has been carried out. Comparison with a reference spectrophotometric procedure has been reported and discussed.[...
Glucose oxidase/hexokinase electrode for the determination of ATP
No full textA hydrogen peroxide based enzyme electrode for the determination of ATP has been developed by the immobilization of glucose oxidase and hexokinase. Competition between the enzymes for the substrate glucose allowed the measurement of ATP. Different immobilization procedures and different types of hexokinase have been tested. Using a BSA-glutaraldehyde procedure and hexokinase from an overproducing strain of bakers' yeast, ATP was measured in the 0.05-0.5 mmol l(-1) range with a detection limit of 0.01 mmol l(-1). ATP concentrations comparable to those reported in the literature and a good recovery were obtained when the enzyme electrode was used with human erythrocyte hemolysate.[...
Phenol Profiling and Nutraceutical Potential of Lycium spp. Leaf Extracts Obtained with Ultrasound and Microwave Assisted Techniques
Get PDFIn recent years, agricultural and industrial residues have attracted a lot of interest in the recovery of phytochemicals used in the food, pharmaceutical, and cosmetic industries. In this paper, a study on the recovery of phenol compounds from Lycium spp. leaves is presented. Ultrasound‐assisted extraction (UAE) and microwave‐assisted extraction (MAE) have been used with alcoholic and hydroalcoholic solvents. Methanolic UAE was the most successful technique for extracting phenols from Lycium leaves, and we used on leaves from L. barbarum and L. chinense cultivated in Italy. The extracts were then characterized as regards to the antioxidant properties by in vitro assays and the phenol profiling by a high performance liquid chromatography‐diode array detector (HPLC‐DAD). Chlorogenic acid and rutin were the main phenol compounds, but considerable differences have been observed between the samples of the two Lycium species. For example, cryptochlorogenic acid was found only in L. barbarum samples, while quercetin‐3‐O‐rutinoside‐7‐O‐glucoside and quercetin‐3‐O‐sophoroside‐7‐O‐rhamnoside only in L. chinense leaves. Finally, multivariate statistical analysis techniques applied to the phenol content allowed us to differentiate samples from different Lycium spp. The results of this study confirm that the extraction is a crucial step in the analytical procedure and show that Lycium leaves represent an interesting source of antioxidant compounds, with potential use in the nutraceutical field
Evaluation of reconfiguration cost and energy aware virtual network embedding policies
No full textNetwork virtualization techniques allow for the coexistence of many virtual networks hosted in a same substrate network. Virtual router migrations allow for resource consolidation with the consequence to reduce the power consumption in low traffic periods. Unfortunately virtual router migrations have the effect of degrading the Quality of Service during the downtime in which the router is not able to carry on its forwarding function. For this reason, despite the advantages in power consumption saving, the migration technique should be applied with parsimony to avoid an excessive QoS degradation. The objective of this paper is to study Virtual Network Embedding problems aware of both operation and reconfiguration costs that are characterized by the energy consumption and the revenue loss due to QoS degradation. An Embedding Optimization Problem formulation will be given in which the objective is to minimize an objective function taking into account both the operation and reconfiguration costs. Because the problem is NP-hard, we propose a feasible solution to the problem in cycle-stationary traffic scenario and when the possible embeddings are a-priory determined. The solution consists in determining the optimal policy of a Markov Decision Process. The results obtained show how the application of the introduced solution allows for cost reduction in the order of 30% as well as to limit the reconfiguration costs with respect to traditional migration policies
Development of oxygen microsensors for monitoring cyanobacterial photosynthesis in Roman hypogea
No full textClark type oxygen microsensors were developed for measurement of photosynthetic light response in cyanobacteria isolated from epilithic microbial communities colonizing Roman hypogea. Microelectrodes were built using polyester or tenon insulated platinum wires as working electrodes and silver wires as reference electrodes, then inserted in glass capillaries previously coated at one end with a silicon gas-permeable membrane. Platinum was polarized at -750 mV vs Ag/AgCl, and 0.1 M KCI was used as supporting electrolyte. Stability, sensitivity and reproducibility of the probes were tested. These cost effective sensors exhibited comparable behaviour with those commercially available. Photosynthesis of selected cyanobacterial species was followed by monitoring the oxygen evolution at increasing irradiances (P/I curves).[...
Electrochemical probe for polyamines detection in biological fluids
No full textThe enzyme polyamine oxidase from maize has been purified and covalently immobilized onto polymeric supports to assemble a polyamine electrochemical biosensor. The enzyme has been used in conjunction with either an O-2 or a H2O2 electrode. The analytical behaviour of this enzyme electrode has been studied with respect to sensitivity, selectivity, optimum pH and buffer, response time and lifetime. Recovery studies performed on urine samples demonstrated that the polyamine biosensor developed can be successfully used to measure polyamines in biological fluids.[...
Electrochemical biosensors for monitoring malolactic fermentation in red wine using two strains of Oenococcus oeni
No full textAmperometric biosensors for the determination Of L-malic and L-lactic acids were optimised and used to monitor micro-malolactic fermentations (micro-MLFs) in red wine. Platinum-based probes, coupled with appropriate enzymes, were assembled in electrochemical flow-injection analysis systems. A classical lactate oxidase based sensor was used for L-lactic acid, while L-malic acid was detected via a new biosensor based on the malic enzyme immobilised in a reactor using phenazine methosulphate as mediator. After a preliminary optimisation phase, a recovery study to evaluate the effect of the matrix (red wine) on biosensor performance was carried out by the addition of different standard solutions of the two analytes to the samples. Recoveries from 93 to 100% and from 94 to 102% were observed for L-malic acid and L-lactic acid, respectively. These optimised biosensors were finally employed to monitor micro-MLFs induced by inoculation of two different strains of Oenococcus oeni into red wine. During the micro-MLFs, samples of wine were collected and assayed for L-malic, L-lactic, and citric acids by use of both biosensors and spectrophotometric techniques. In parallel the viable bacterial cell count was also evaluated. The kinetics of bacterial growth, degradation Of L-malic and citric acids, and production Of L-lactic acid was found to be a function of the strains inoculated. (C) 2003 Elsevier B.V. All rights reserved.[...
Amperometric ammonium ion and urea determination with enzyme-based probes
No full textAmperometric enzyme probes for ammonium and urea have been assembled and evaluated using immobilized glutamate dehydrogenase and urease enzymes coupled with platinum electrodes. Analytical parameters such as pH, buffer, temperature, probe life-time, enzyme immobilization, cofactor concentration and response time have been optimized. Ammonium was detected in the range 10(-5)-3 x 10(-4) mol l(-1). Better reproducibility and stability were achieved using the enzyme GLDH type III and NADH at a concentration of 10(-3) mol l(-1). Urea has been determined in the range 10(-5)-3 x 10(-4) mol l(-1) using the enzyme urease first in solution and then immobilized on nylon net. The analysis was based on an amperometric measurement which gives a linear relationship between current and analyte concentration. This considerably improved the sensitivity of the analysis when compared with the potentiometric-based procedures. Moreover, this method does not suffer from the potassium ion interference which affects the potentiometric nonactin-based NH4+ electrodes. Analysis of ammonium and urea were carried out in standard solutions and in saliva samples. Results compared with a spectrophotometric reference procedure correlated well.[...
GC-MS aroma characterization of vegetable matrices: Focus on 3-alkyl-2-methoxypyrazines
No full text3-Alkyl-2-methoxypyrazines (MPs) are a very important class of volatile organic compounds (VOCs), intensively characterizing the aroma of several food products including fruits and vegetables. Due to the very low orthonasal sensory threshold, low amounts of MPs may act as key positive or negative aroma compounds. The analysis of these volatiles in foods is then remarkably important, and it may be very challenging as confirmed by the scarce literature focused on MPs, particularly with respect to quantitative data. In the attempt to fill this gap, in this work, presence and quantification of MPs in four different vegetables, namely, green bell pepper (Capsicum annuum L. var grossum), green pea (Pisum sativum L. and Pisum spp), carrot (Daucus carota subsp sativus), and cucumber (Cucumis sativus L.) have been investigated. Two different volatile extraction techniques (solid phase microextraction [SPME] and simultaneous distillation-extraction [SDE]) in conjunction with VOC qualitative analysis by gas chromatography-mass spectrometry (GC-MS) methods were applied. Solid phase microextraction coupled with GC-MS in single ion monitoring (SIM) mode showed the best performances in sensitivity to detect MPs on the different vegetable matrices. Therefore, a headspace (HS) SPME-GC-MS quantitative method was developed and optimized, and dominant MPs quantified. 3-Isopropyl-2-methoxypyrazine (IPMP), 3- sec-butyl-2-methoxypyrazine (sBMP), and 3-isobutyl-2-methoxypyrazine (IBMP) have been detected and quantified in all the vegetables. 3-Isopropyl-2-methoxypyrazine was the prevalent MP in peas and cucumber while IBMP in bell pepper. These MPs were detected for the first time in carrot and cucumber. Finally, sBMP has been confirmed to be the most important MP in carrot. The developed method allowed to characterize the VOC pattern and, in particular, to quantify MPs in four vegetables. Results highlight the feasibility of further applications of the analytical approach to determine MPs in other food matrices where an excessive amount of these aromas may negatively affect their flavor (eg, coffee)
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