Andrei Florin Danet

Total antioxidant capacity of some commercial fruit juices: electrochemical and spectrophotometrical approaches.

The aim of this paper was to assess the total antioxidant capacity of some commercial fruit juices (namely citrus), spectrophotometrically and by the biamperometric method, using the redox couple DPPH· (2,2-diphenyl-1-picrylhydrazyl)/DPPH (2,2-diphenyl-1-picrylhydrazine). Trolox® was chosen as a standard antioxidant. In the case of the spectrophometric method, the absorbance decrease of the DPPH· solution was followed. For the biamperometric method, the influence of some parameters like the potential diference, ΔE, DPPH· concentration, and Trolox® concentration was investigated. The calibration graph obtained for Trolox® presents linearity between 5 and 30 µM, (y = 0.059 x + 0.0564, where y represents the value of current intensity, expressed as μA and x the value of Trolox® concentration, expressed as μM; r2 = 0.9944). The R.S.D. value for the biamperometric method was 1.29% (n = 10, c = 15 μM Trolox®). In the case of the spectrophotometric method, the calibration graph obtained for Trolox® presents linearity between 0.01 and 0.125 mM (y = -9.5789 x+1.4533, where y represents the value of absorbance and x, the value of Trolox® concentration, expressed as mM; r2 = 0.9963). The R.S.D. value for the spectrophotometric method was 2.05%. Both methods were applied to total antioxidant activity determination in real samples (natural juices and soft drinks) and the results were in good agreement.

Exogenous oxidative stress induces Ca2+ release in the yeast Saccharomyces cerevisiae

The Ca2+‐dependent response to oxidative stress caused by H2O2 or tert‐butylhydroperoxide (tBOOH) was investigated in Saccharomyces cerevisiae cells expressing transgenic cytosolic aequorin, a Ca2+‐dependent photoprotein. Both H2O2 and tBOOH induced an immediate and short‐duration cytosolic Ca2+ increase that depended on the concentration of the stressors. Sublethal doses of H2O2 induced Ca2+ entry into the cytosol from both extracellular and vacuolar sources, whereas lethal H2O2 shock mobilized predominantly the vacuolar Ca2+. Sublethal and lethal tBOOH shocks induced mainly the influx of external Ca2+, accompanied by a more modest vacuolar contribution. Ca2+ transport across the plasma membrane did not necessarily involve the activity of the Cch1p/Mid1p channel, whereas the release of vacuolar Ca2+ into the cytosol required the vacuolar channel Yvc1p. In mutants lacking the Ca2+ transporters, H2O2 or tBOOH sensitivity correlated with cytosolic Ca2+ overload. Thus, it appears that under H2O2‐induced or tBOOH‐induced oxidative stress, Ca2+ mediates the cytotoxic effect of the stressors and not the adaptation process.

Flow injection system with chemiluminometric detection for enzymatic determination of ascorbic acid.

A simple, selective and rapid method for determination of ascorbic acid from fruit juices was developed by combining a flow injection analysis (FIA) system with a chemiluminometric detector and a reactor with L-ascorbate oxidase immobilized on controlled pore glass. It was found that some reducing agents (eg ascorbic acid and mercaptoacetic acid) give chemiluminescence with luminol in the presence of hexacyanoferrate (III) in an alkaline solution. We used this new type of chemiluminescent reaction for the enzymatic determination of ascorbic acid. The background substraction method was used in order to avoid interference during ascorbic acid determination. Accordingly, two chemiluminometric signals were registered for each determination, one signal corresponding to the sample that passed through the enzymatic reactor that decomposed the ascorbic acid completely, and the second signal corresponding to the sample that does not pass through the reactor. The difference between the two signals corresponds to ascorbic acid from the sample. The linear range of the method was 10-1000 micromol/L of ascorbic acid and the detection limit was 5 micromol/L The throughput was four samples/h and RSD 3.13% (n = 10). This method was applied for determination of ascorbic in fruit juices. The results were compared with those found by the reference method, based on titrimetric determination with 2,6-dichlorophenolindophenol, and the concordance was excellent.

Mercury Determination in Fish Samples by Chronopotentiometric Stripping Analysis Using Gold Electrodes Prepared from Recordable CDs

A simple method for manufacturing gold working electrodes for chronopotentiometric stripping measurements from recordable CD-Rs is described. These gold electrodes are much cheaper than commercially available ones. The electrochemical behavior of such an electrode and the working parameters for mercury determination by chronopotentiometric stripping analysis were studied. Detection limit was 0.30 μg Hg/L and determination limit was 1.0 μg Hg/L for a deposition time of 600 s. Using the developed working electrodes it was possible to determine the total mercury in fish samples. A method for fish sample digestion was developed by using a mixture of fuming nitric acid and both concentrated sulfuric and hydrochloric acids. The recovery degree for a known amount of mercury introduced in the sample before digestion was 95.3% (n=4).

Calcium signaling mediates the response to cadmium toxicity in Saccharomyces cerevisiae cells

The involvement of Ca2+ in the response to high Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Hg2+ was investigated in Saccharomyces cerevisiae. The yeast cells responded through a sharp increase in cytosolic Ca2+ when exposed to Cd2+, and to a lesser extent to Cu2+, but not to Mn2+, Co2+, Ni2+, Zn2+, or Hg2+. The response to high Cd2+ depended mainly on external Ca2+ (transported through the Cch1p/Mid1p channel) but also on vacuolar Ca2+ (released into the cytosol through the Yvc1p channel). The adaptation to high Cd2+ was influenced by perturbations in Ca2+ homeostasis. Thus, the tolerance to Cd2+ often correlated with sharp Cd2+‐induced cytosolic Ca2+ pulses, while the Cd2+ sensitivity was accompanied by the incapacity to rapidly restore the low cytosolic Ca2+.

Flow Injection Determination Of L-Ascorbic Acid in Natural Juice with Biamperometric Detection

Abstract A flow-injection system with biamperometric detection for L-ascorbic acid (vitamin C) determination was designed. The method is based on L-ascorbic acid oxidation to dehydroascorbic acid, in acidic medium, using iodine-iodide solution as oxidizing reagent. The iodine amount consumed in the redox reaction was biaperometrically detected and it was proportional to the amount of L-ascorbic acid from the sample. The calibration graph was linear over the range of concentration 5×10−5-5×10−4 M of vitamin C. The RSD for a 2.5×10−4 M standard solution of vitamin C was 1.08% (n=10) and the throughput was 60 samples h−1. The selectivity of the proposed FIA method was verified using an ascorbate oxidase solution as carrier stream. It was found that L-ascorbic acid could be determined in natural products with a good selectivity and rapidity.

Flow injection determination of chloride ions with spectrophotometric detection

Abstract A single-line FIA system with a stream-sample splitting device for chloride determination is presented. The analytical method is based on the Fe3+/Hg(SCN)2/Cl− system and the absorbance of the red Fe(SCN)2+ species monitored spectrophotometrically at 480 nm. Using a stream-sample splitting device, the recorded signal is composed of two merged peaks. Three calibration curves were obtained, once injecting the standard solution series, two using the maximum heights of P1 and P2 peaks and one using the height of T trough. The FIA system showed three linear responses to the concentration of chloride in the ranges 10-100 ppm (P1); 10-500 ppm (P2) and 20-1000 ppm (T), respectively. Also, it was capable of detecting chloride ions in different types of water with a throughput of 15 samples h−1 and the RSD for 240 ppm of Cl− (n=10) were 1.67% (P1); 2.38% (P2) and 1.23% (T), respectively. The interference of several ions (commonly found in water) on the FIA outputs was investigated.

Flow analysis for determination of paraoxon with use of immobilized acetylcholinesterase reactor and new type of chemiluminescent reaction

A highly sensitive flow analysis method for determination of acetylcholinesterase (AChE) inhibitors like organophosphorous pesticides using a new chemiluminescent reaction was developed and optimized. This method is fast, sensitive, and cheap, because it requires only one enzyme and its substrate. The system incorporates a reactor with immobilized AChE on controlled pore glass (CPG) and a chemiluminometric detector. Variations in enzyme activity due to inhibition are measured from the changes of concentrations of thiocholine produced when the substrate (acetylthiocholine chloride) is pumped before and after the passage of the solution containing the pesticide through the immobilized AChE reactor. Thiocholine is determined by a new chemiluminescent reaction with luminol in the presence of potassium ferricyanide. The percentage inhibition of enzyme activity is correlated to the pesticide concentration. The inhibited enzyme is reactivated by 10 mM pyridine-2-aldoxime methiodide (2-PAM). The experimental conditions were first optimized for activity determination of the effect of pH, flow rates, and Tris concentrations. For the measurement of AChE inhibition, the appropriate concentration of the substrate is selected such that the rate of noninhibited reaction can be considered unchanged and could be used as a reference. For optimization of experimental conditions for inhibition, several parameters of the system are studied and discussed: flow rate, enzyme-pesticide contact time, luminol concentration, ferricyanide concentration, 2-PAM concentration, and configuration of the FIA manifold. Paraoxon, an organophosphorous pesticide was tested. For an inhibition time of 10 min the calibration graph is linear from 0.1 to 1 ppm paraoxon with a relative standard deviation (n = 5) of 4.6% at 0.5 ppm. For an inhibition time of 30 min the calibration graph is linear from 25 to 250 ppb paraoxon.

Total Antioxidant Activity and Phenols and Flavonoids Content of Several Plant Extracts

Alcoholic extracts of six culinary and medicinal plants have been analyzed for their antioxidative properties. Extracts were obtained by continuous (Soxhlet) and ultrasounds extraction. A new flow injection analysis method with chemiluminescence detection based on a luminol/Co(II)/EDTA/H2O2 system was set up for the total antioxidant capacity determination of the studied extracts. For comparison, total phenols and flavonoids contents of plant extracts were determined by spectrophotometric methods. A good correlation between total phenols and total antioxidant capacity was found for some determinations.

Recent Applications for in Vitro Antioxidant Activity Assay

ABSTRACT This review presents some of the most recent aspects related to antioxidants and the basic kinetic models of inhibited autoxidation and analyzes the chemical principles of antioxidant capacity assays. Taking into account the reactions involved, in the antioxidant activity determinations, the assays can be classified into two main types: hydrogen atom transfer reactions and electron transfer. This review focuses on analytical methods used for antioxidant activity assay, published in the period 2009–2014.