Julián Zapata

Analysis, occurrence, and potential sensory significance of five polyfunctional mercaptans in white wines.

A previously developed analytical method has been improved, validated and adapted for the analysis of 2-furfurylthiol (FFT), 4-methyl-4-mercapto-2-pentanone (MP), 3-mercaptohexyl acetate (MHA), 3-mercaptohexanol (MH) and benzylmercaptan (BM) in 136 white wines from different parts of the world. The overall uncertainty of the determinations was found to be around 20%, which was considered satisfactory given the low levels at which these compounds are found. The levels ranged from the method detection limits (0.5; 0.6; 2.0; 8.0 and 0.5 ng/L for FFT, MP, MHA, MH and BM, respectively) to 225; 87.9; 591; 7255 and 131 ng/L, which implies that nearly all of them can reach more than 100 Odor Units in some wines. The levels are significantly linked to both the grape variety (with the exception of FFT) and to the origin (in the case of Sauvignon Blanc samples), however, the range of variation within groups are so large that clear clusters could not be observed. Different sensory tests carried out on white wine models showed that all these compounds, even at low concentration, play an outstanding role on the aroma of wine, contributing to fruity, fresh and green notes. In some wines they are at concentrations high enough to act as genuine impact compounds.

Comparison of extraction techniques and mass spectrometric ionization modes in the analysis of wine volatile carbonyls.

This work presents a comparative study of the analytical characteristics of two methods for the analysis of carbonyl compounds in wine, both based on the derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA). In the first method derivatives are formed in the solid phase extraction (SPE) cartridge in which the analytes have been previously isolated, while in the second method derivatives are formed in a solid phase microextraction (SPME) fibre saturated with vapors of the reagent and exposed to the sample headspace. In both cases detection has been carried out by electron impact (EI) or negative chemical ionization (NCI) mass spectrometry. The possibility of determining haloanisols simultaneously has been also considered. The method based on SPE presents, in general, better analytical properties than the SPME one. Although linearity was satisfactory for both methods (R(2)>0.99), repeatability of the SPE method (RSD<10%) was better than that obtained with SPME (9% < RSD < 20%). Detection limits obtained with EI are better for the SPE method except for trihaloanisols, while with NCI detection limits for both strategies are comparable, although the SPME strategy presents worse results for ketones and methional. Detection limits are always lower with NCI, being the improvement most notable for SPME. Recovery experiments show that in the case of SPE, uncertainties are lower than 12% in all cases, while with the SPME method the imprecision plus the existence of matrix effects make the global uncertainty to be higher than 15%.

Automated and quantitative headspace in-tube extraction for the accurate determination of highly volatile compounds from wines and beers

An automatic headspace in-tube extraction (ITEX) method for the accurate determination of acetaldehyde, ethyl acetate, diacetyl and other volatile compounds from wine and beer has been developed and validated. Method accuracy is based on the nearly quantitative transference of volatile compounds from the sample to the ITEX trap. For achieving that goal most methodological aspects and parameters have been carefully examined. The vial and sample sizes and the trapping materials were found to be critical due to the pernicious saturation effects of ethanol. Small 2 mL vials containing very small amounts of sample (20 μL of 1:10 diluted sample) and a trap filled with 22 mg of Bond Elut ENV resins could guarantee a complete trapping of sample vapors. The complete extraction requires 100 × 0.5 mL pumping strokes at 60 °C and takes 24 min. Analytes are further desorbed at 240 °C into the GC injector under a 1:5 split ratio. The proportion of analytes finally transferred to the trap ranged from 85 to 99%. The validation of the method showed satisfactory figures of merit. Determination coefficients were better than 0.995 in all cases and good repeatability was also obtained (better than 7% in all cases). Reproducibility was better than 8.3% except for acetaldehyde (13.1%). Detection limits were below the odor detection thresholds of these target compounds in wine and beer and well below the normal ranges of occurrence. Recoveries were not significantly different to 100%, except in the case of acetaldehyde. In such a case it could be determined that the method is not able to break some of the adducts that this compound forms with sulfites. However, such problem was avoided after incubating the sample with glyoxal. The method can constitute a general and reliable alternative for the analysis of very volatile compounds in other difficult matrixes.

Multiple automated headspace in-tube extraction for the accurate analysis of relevant wine aroma compounds and for the estimation of their relative liquid-gas transfer rates

An automated headspace in-tube extraction (ITEX) method combined with multiple headspace extraction (MHE) has been developed to provide simultaneously information about the accurate wine content in 20 relevant aroma compounds and about their relative transfer rates to the headspace and hence about the relative strength of their interactions with the matrix. In the method, 5 μL (for alcohols, acetates and carbonyl alcohols) or 200 μL (for ethyl esters) of wine sample were introduced in a 2 mL vial, heated at 35°C and extracted with 32 (for alcohols, acetates and carbonyl alcohols) or 16 (for ethyl esters) 0.5 mL pumping strokes in four consecutive extraction and analysis cycles. The application of the classical theory of Multiple Extractions makes it possible to obtain a highly reliable estimate of the total amount of volatile compound present in the sample and a second parameter, β, which is simply the proportion of volatile not transferred to the trap in one extraction cycle, but that seems to be a reliable indicator of the actual volatility of the compound in that particular wine. A study with 20 wines of different types and 1 synthetic sample has revealed the existence of significant differences in the relative volatility of 15 out of 20 odorants. Differences are particularly intense for acetaldehyde and other carbonyls, but are also notable for alcohols and long chain fatty acid ethyl esters. It is expected that these differences, linked likely to sulphur dioxide and some unknown specific compositional aspects of the wine matrix, can be responsible for relevant sensory changes, and may even be the cause explaining why the same aroma composition can produce different aroma perceptions in two different wines.

Simultaneous determination of free and bonded forms of odor-active carbonyls in wine using a headspace solid phase microextraction strategy

This paper presents a new strategy for the direct evaluation of odor-active carbonyls in the wine headspace and for the simultaneous estimation of their amounts in odorless bonded forms. In the final developed strategy, 25 mL of wine are spiked with internal and surrogate standards and let to equilibrate for at least 12 h in an oxygen-free chamber. Ten milliliter of the sample are then transferred to a standard headspace vial. Carbonyls in the headspace are preconcentrated on a PDMS/DVD fiber keeping the sample unstirred at 45°C for just 10 min and are further analyzed on a GC-MS equipped with a quadrupole in SIM mode. Normalized peak analyte areas interpolated in calibration plots built with synthetic wines give estimations of the concentrations of free forms, while the ratios of the areas of surrogates observed in wines to those observed in synthetic wine make it possible to get estimations of the proportion of each analyte present in bonded non-volatile form. The validity of this approach has been demonstrated both via standard recovery experiments and via the analysis of samples previously incubated with glyoxal in order to break aldehyde-bisulfite complexes. In general, method detection limits (below 1 μg L(-1)), precision (RSD (%)<10%) and accuracy are satisfactory for 12 studied carbonyls. Results demonstrate that wine contain relevant amounts of aldehydes (more than 95% in some cases) in the form of reversible odorless complexes, supporting a previous observation about the potential implication of these complexes on the development of oxidized aroma.

Aroma compounds and sensory characteristics of Arneis Terre Alfieri DOC wines: the concentration of polyfunctional thiols and their evolution in relation to different ageing conditions

Abstract Arneis is an Italian autochthonous white grape cultivar. This study involved investigating the chemicophysical, aromatic composition and sensory evaluation of Arneis wine in relation to different oenological practices during winemaking and ageing. For the first time, polyfunctional thiols related aromas were identified above their perception threshold in Arneis wine. Moreover, citrus, grapefruit and tropical fruit notes characterized this wine during the first month of ageing, thus suggesting a strong correlation between chemical and sensory results. The concentration of thiols decreased rapidly during the first month of ageing, together with the tropical fruit notes. In particular, the perception of the grapefruit note of the wine decreased in association with the 3-mercaptohexyl acetate content in both the barrel and stainless steel (ST) aged wines. Moreover, the ageing technique clearly affected wine composition and sensory profile; barrel aged wines were characterized both by vanilla and honey notes, and a weaker perception of thiols despite containing a similar concentration to ST aged wines. Within this study, the ability of glutathione to decrease the oxidation of volatile thiols in Arneis wine was confirmed, but under experimental conditions employed, the addition of reduced glutathione did not lead to any statistically significant differences in sensory results.

Application of a new sampling device for determination of volatile compounds released during heating olive and sunflower oil: sensory evaluation of those identified compounds

This work has applied a system for characterizing volatile compounds generated during the heating of oils, based on solid-phase extraction–gas chromatography–mass spectrometry. The system has been applied to sunflower and extra virgin olive oil at kitchen conditions, heating from room temperature to 80° above their smoking point. The work identified twenty-three compounds, mainly saturated and unsaturated aldehydes, and alkanes; carboxylic acids were present in lower concentrations. During heating, the stability of each oil was found to be different. The alkanals were produced in greater quantities in the sunflower oil. Alkanes were found in higher concentration in the olive oil and showed no significant variation in either of the oils as the temperature changed. And a relationship between the quantity of aldehydes released at the highest temperature and the percentage of fatty acids from which those aldehydes originated in each oil was found. The importance of the unsaturated aldehydes in the deep-fried odor was also exposed in this study.

Fast and fully automated analytical method for the screening of residues of aziridine and 2-chloroethylamine in pharmaceutical active principles

A simple, fast and fully automated method for the screening of aziridine (AZD) and 2-chloroethylamine (CEA) in active pharmaceutical ingredients (API) has been developed. The method is based on the in-fiber derivatization of the amines extracted from the sample headspace (previously dissolved or suspended in alkaline water) with 2,3,4,5,6-pentafluorobenzoyl chloride (PFBCl) previously adsorbed in the PDMS/DVB solid phase microextraction (SPME) fiber. The derivatives formed are further desorbed and analyzed in a gas chromatograph with negative ion chemical ionization mass spectrometry (GC-NCI-MS) using methane as reagent gas. The different operational parameters of the procedure have been optimized to get highest sensitivity. The validation of the method, however, revealed a poor repeatability, particularly evident in water-soluble APIs (RSD>20% for AZD). In spite of that, the low detection limits (1-3ngg(-1) for AZD and CEA), speed (44min total analysis time) and automation make that this method can be satisfactorily used as screening tool to accept or reject API batches attending to their volatile amine content and a critical specified value derived from the 1.5μg/day Threshold of Toxicological Concern (TTC) and maxima daily dosages. This was shown by analyzing seventy-five fluvoxamine maleate samples containing known levels of AZD and CEA (between 0.05 and 1.05μgg(-1)) in intermediate reproducibility conditions to get reliable estimations of precision and linearity. From these data, acceptance, rejection and non-conclusive areas of response are defined for both analytes at different confidence and replication levels using normal statistics. The method was satisfactorily applied to real fluvoxamine maleate samples.

A Robust SPME Method for the Analysis of Wine Volatiles based on Multiple Internal Standards and Multivariate Regression

The analytical signals obtained by SPME are extremely sensitive to experimental parameters affecting liquid-gas and gas-solid distribution coefficients, such as alcoholic degree, non-volatile composition or wine content in major fermentation volatiles. In order to measure the weight of these factors and to design a robust calibration, synthetic but real-like wines containing selected analytes, a cocktail with 13 different internal standards and variable amounts of ethanol, non-volatile constituents, and major volatile compounds were prepared. Data revealed that the wine content in major volatile constituents affected the extraction of most analytes, while ethanol level and matrix composition specifically affected the least volatile components. In 29 out of 65 cases, a single internal standard provided a robust calibration, while in 30 other cases a mathematical combination of the 13 internal standards obtained by PLSR provided maxima accuracy.