Raquel Rial-Otero

Determination of 23 pesticide residues in leafy vegetables using gas chromatography–ion trap mass spectrometry and analyte protectants

A gas chromatographic method was developed for simultaneously determining residues of 12 insecticides (acrinathrin, bifenthrin, carbofuran, cyfluthrin, lambda-cyhalothrin, cypermethrin, chlorfenvinphos, deltamethrin, esfenvalerate, fenamiphos, methiocarb and tau-fluvalinate) and 11 fungicides (cyprodinil, fludioxonil, iprodione, metalaxyl, penconazole, pyrimethanil, procymidone tebuconazole, triadimefon, triadimenol and vinclozolin) in leafy vegetables. Samples were extracted with acetonitrile and cleaned-up with graphitized carbon black/primary secondary amine (GCB/PSA) solid-phase extraction (SPE) cartridges using acetonitrile:toluene (3:1, v/v) as eluent. The eluate was finally evaporated and redissolved with 0.5 mL of acetone containing the internal standards (pentachlorobenzene and fenpropathrin) and three analyte protectants (3-ethoxy-1,2-propanediol, d-sorbitol and l-gulonic acid gamma-lactone). The addition of analyte protectants allows to avoid the matrix-induced response enhancement effect on quantitation process with absolute recoveries ca. 100%. Precision (expressed as relative standard deviation) was lower than 10% for all pesticides and finally, limits of detection were also 10-20 times lower than maxima residue levels (MRLs) established by European Regulation. The proposed method was applied to determine pesticide residues in commercial leafy vegetables (lettuce, Swiss chard and spinach) purchased from markets in Orense (NW Spain). Pesticide residues were detected in 84% of the total samples (63 from 75 samples) and pesticide concentrations were higher than MRL in 18 samples.

A Review on the Fate of Pesticides during the Processes within the Food-Production Chain

Only the intake of toxicologically-significant amounts can lead to adverse health effects even for a relatively toxic substance. In the case of residues in foods this is based on two major aspects—first, how to determine quantitatively the presence of a pollutant in individual foods and diets, including its fate during the processes within the food production chain; and second, how to determine the consumption patterns of the individual foods containing the relevant pollutants. The techniques used for the evaluation of the fate of pesticides during food processing have been critically reviewed in this paper to determine those areas where improvements are needed or desirable. Options for improvements are being suggested, including, for example, the development of a pan-European food composition database, activities to understand better effects of processing on individual food pesticides, and harmonization of food consumption survey methods with the option of a regular pan-European survey. The ultimate aim is to obtain appropriate estimations for the presence and quantity of a given chemical in a food and in the diet in general. Existing pragmatic approaches are a first crude step to model food pollutant intake. It is recommended to extend, refine, and validate this approach in the near future. This has to result in a cost-effective exposure-assessment system to be used for existing and potential categories of pollutants. This system of knowledge (with information on sensitivities, accuracy, etc.) will guide future data collection.

Wine Aroma Compounds in Grapes: A Critical Review

Volatile organic compounds are vital to wine quality, determining their aroma and varietal characteristics. Which are present, and in what quantity, depends on the cultivar, the situation and soil of the vineyard, weather, cultivation methods, and wine-making practices. Here, we review the literature on the development of wine aroma compounds in grapes, and how it is affected by the above-named factors. Increasing understanding of these processes at the molecular level will aid vine growers in the optimal selection of harvest dates and other decisions favoring the consistent production of balanced, flavorful berries.

Effect of organic matter and iron oxides on quaternary herbicide sorption-desorption in vineyard-devoted soils.

Herbicide soil/solution distribution coefficients (K(d)) are used in mathematical models to predict the movement of herbicides in soil and groundwater. Herbicides bind to various soil constituents to differing degrees. The universal soil colloid that binds most herbicides is organic matter; however metallic hydrous oxides might also have some influence. The adsorption-desorption of three quaternary ammonium herbicides on soils with different chemical-physical characteristics was determined using a batch equilibration method before and after the following sequential selective dissolution procedures: removal of organic matter, and removal of organic matter plus free iron oxides. The experimentation involved paraquat (PQ), diquat (DQ) and difenzoquat (DFQ) herbicides. The distribution coefficients (K(d)) of the molecules and their correlation to the soil components were determined and a significant negative correlation with organic carbon was highlighted (r<-0.610, p<0.035, n=12). All quats cations experiment high adsorption in the control soils with a Zeta potential at about -21 mV. The order of adsorption on soils (based on K(d)) was the following: PQ>DQ>>DFQ. The adsorption isotherms of these three herbicides on the natural and processed soils were satisfactorily fitted with the Freundlich equation, and a significant correlation with organic carbon was highlighted for quats K(F) (r<-0.696, p<0.012, n=12). The removal of organic matter from soils seems to leave free new adsorption sites for quats on the clay surface, which is no longer occluded by organic matter. This work shows that the amount and nature of the surface that remains available after the removal of single soil constituents is a critical parameter in determining the sorptive behavior of cationic contaminants.

A Review on the Fermentation of Foods and the Residues of Pesticides—Biotransformation of Pesticides and Effects on Fermentation and Food Quality

Residues of pesticides in food are influenced by processing such as fermentation. Reviewing the extensive literature showed that in most cases, this step leads to large reductions in original residue levels in the fermented food, with the formation of new pesticide by-products. The behavior of residues in fermentation can be rationalized in terms of the physical-chemical properties of the pesticide and the nature of the process. In addition, the presence of pesticides decrease the growth rate of fermentative microbiota (yeasts and bacterias), which provokes stuck and sluggish fermentations. These changes have in consequence repercussions on several aspects of food sensory quality (physical-chemical properties, polyphenolic content, and aromatic profile) of fermented food. The main aim of this review is to deal with all these topics to propose challenging needs in science-based quality management of pesticides residues in food.

Effects of Sugar Concentration Processes in Grapes and Wine Aging on Aroma Compounds of Sweet Wines—A Review

Dessert sweet wines from Europe and North America are described in this review from two points of view: both their aroma profile and also their sensorial description. There are growing literature data about the chemical composition and sensory properties of these wines. Wines were grouped according to the production method (concentration of sugars in grapes) and to the aging process of wine (oxidative, biological, or a combination of both and aging in the bottle). It was found that wines natively sweets and wines fortified with liquors differ in their volatile compounds. Sensory properties of these wines include those of dried fruit (raisins), red berries, honey, chocolate and vanilla, which is contributing to their growing sales. However, there is still a need for scientific research on the understanding of the mechanisms for wine flavor enhancement.

Behaviour of metalaxyl as copper oxychloride–metalaxyl commercial formulation vs. technical grade-metalaxyl in vineyards-devoted soils

The objective of this work is to asses the sorption of metalaxyl applied as a copper oxychloride (CO)-metalaxyl formulation, for a set of selected soils devoted to vineyards. The method involved batch incubation of soils suspended with a commercial copper oxychloride-metalaxyl-based fungicide in 0.01M CaCl(2). Afterwards, the metalaxyl concentration remaining in solution was determined by high-performance liquid chromatography (HPLC). The amount of dissolved metalaxyl in the fungicide suspension depends mainly on the soil pH, its potential acidity, and the cation exchange capacity. Of the approx. 20% metalaxyl retained by the solid colloids, the effect of organic matter colloids in soils (15-20 mg kg(-1)) had a poor contribution (six times lower) than the copper oxychloride colloids (40%, w/w) in the commercial fungicide formulation (100-130 mg kg(-1)). When comparing these retention data with the behaviour of metalaxyl used as a technical grade fungicide of about 100% purity (10-15 mg kg(-1) in solids), it is clear that the commercial formulation increases a 30% retention of metalaxyl by soil (15-20 mg kg(-1) in solids). The overall effect of the metalaxyl formulation plus soil show values of 10 times higher retention than technical grade-metalaxyl plus soil. Commercial formulation can decrease the mobility of soluble metalaxyl in agricultural soils with regard to the expected values obtained from batch studies using analytical grade-metalaxyl. Therefore, the effect of surfactants should be considered in the assessment of water contamination by the pesticides used in agriculture.

Thermodynamics of sodium dodecyl sulphate-salicylic acid based micellar systems and their potential use in fruits postharvest

Micellar systems have excellent food applications due to their capability to solubilise a large range of hydrophilic and hydrophobic substances. In this work, the mixed micelle formation between the ionic surfactant sodium dodecyl sulphate (SDS) and the phenolic acid salicylic acid have been studied at several temperatures in aqueous solution. The critical micelle concentration and the micellization degree were determined by conductometric techniques and the experimental data used to calculate several useful thermodynamic parameters, like standard free energy, enthalpy and entropy of micelle formation. Salicylic acid helps the micellization of SDS, both by increasing the additive concentration at a constant temperature and by increasing temperature at a constant concentration of additive. The formation of micelles of SDS in the presence of salicylic acid was a thermodynamically spontaneous process, and is also entropically controlled. Salicylic acid plays the role of a stabilizer, and gives a pathway to control the three-dimensional water matrix structure. The driving force of the micellization process is provided by the hydrophobic interactions. The isostructural temperature was found to be 307.5 K for the mixed micellar system. This article explores the use of SDS-salicylic acid based micellar systems for their potential use in fruits postharvest.

Comparative study of matrices for their use in the rapid screening of anabolic steroids by matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry

New data on sample preparation and matrix selection for the fast screening of androgenic anabolic steroids (AAS) by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) is presented. The rapid screening of 15 steroids included in the World Anti-Doping Agency (WADA) prohibited list using MALDI was evaluated. Nine organic and two inorganic matrices were assessed in order to determine the best matrix for steroid identification in terms of ionisation yield and interference by characteristic matrix ions. The best results were achieved for the organic matrices 2-(4-hydroxyphenylazo)benzoic acid (HABA) and trans-3-indoleacrylic acid (IAA). Good signals for all the steroids studied were obtained for concentrations as low as 0.010 and 0.050 microg/mL on the MALDI sample plate for the HABA and IAA matrices, respectively. For these two matrices, the sensitivity achieved by MALDI is comparable with the sensitivity achieved by gas chromatography/mass spectrometry (GC/MS), which is the conventional technique used for AAS detection. Furthermore, the accuracy and precision obtained with MALDI are very good, since an internal mass calibration is performed with the matrix ions. For the inorganic matrices, laser fluences higher than those used with organic matrices are required to obtain good MALDI signals. When inorganic matrices were used in combination with glycerol as a dispersing agent, an important reduction of the background noise was observed. Urine samples spiked with the study compounds were processed by solid-phase extraction (SPE) and the screening was consistently positive.

Sorption of penconazole applied as a commercial water-oil emulsion in soils devoted to vineyards.

The objective of this work was to assess the effect of surfactants and oils of a commercial formulation on the potential mobility of penconazole in agricultural soils that have been subjected to a high rate of application of agricultural chemicals. Soil-water partition tests on a commercial water-oil emulsion formulation of penconazole (WOEP) in 0.01 M CaCl(2) containing 35 mg L(-1) penconazole, incubated for 24 h, showed a maximum retention of approximately 250-300 mg penconazole kg(-1) soil. Approximately 70% of the total penconazole retained by the solid phase was sorbed on the soil (175-200 mg kg(-1)). The other 30% was retained by the adjuvants present in the commercial formulation. The formulation also influenced the water-soil partition, increasing the sorption in tests on batch studies using technical-grade penconazole (TGP). Soils with high total copper and organic matter had the greatest affinity for penconazole when added as WOEP. Additionally, adsorption of penconazole followed an S-type isotherm, whose behavior was consistent with the ability of the technical-grade penconazole to form aggregates. In the case of the WOEP, the S-type behavior could be attributed to the surfactant present in the formulation, which could be adsorbed onto soil as hemimicelles, which in turn may facilitate adsorption of penconazole.