Ramón Natera

Development of a stir bar sorptive extraction method coupled to gas chromatography-mass spectrometry for the analysis of volatile compounds in Sherry brandy

Sherry brandy (Jerez, SW, Spain) is a high quality distilled beverage derived from wine. Its perceived quality depends, inter alia, on hundreds of flavour compounds. A Stir Bar Sorptive Extraction (SBSE) method coupled to gas chromatography-mass spectrometry has been developed for the analysis of volatile compounds in Sherry brandy. The optimization of the extraction procedure has been carried out using a statistical approach, based on a factorial design. The best overall analytical conditions obtained were the following: 35 mL of sample, diluted 1:1 with Milli-Q water and extraction at 1100 rpm for 100 min. The method has been successfully validated in a further stage of this work. Several performance characteristics such as calibration, linearity, precision (inter- and intra-assay), detection and quantification limits and recovery were studied. Finally, the method developed has been applied to different Sherry brandies. The results obtained show SBSE to be a suitable technique for the reliable analysis of volatile compounds in brandies.

Comparative Analysis of the Organic Acid Content of Vinegar by Capillary Electrophoresis and Ion-Exclusion Chromatography with Conductimetric Detection

SummaryIon-exclusion chromatography (IEC) and capillary electrophoresis (CE) have been compared for determination of organic acids in samples of Sherry wine vinegar. The accuracy of each technique was evaluated by use of the standard addition method. There were no differences between the techniques at a significance level of 5%, except for determination of malic acid by CE. Both analytical methods were used to analyse sixteen samples of Sherry wine vinegar supplied by different producers. The regression coefficients (r2) for analysis by IEC and CE exceeded 0.94 for all acids. Results from both methods were in good agreement and the methods are sufficiently selective and sensitive to be applied directly to sherry wine vinegars.

Development of a new stir bar sorptive extraction method for the determination of medium‐level volatile thiols in wine

A fast, simple, and reliable analytical method for the determination of medium-level volatile thiols in wines is presented. Stir bar sorptive extraction using ethylene glycol-silicone coated stir bars has been used in combination with thermal desorption gas chromatography with mass spectrometry for the analysis of 4-mercapto-4-methylpentan-2-one, 2-furanmethanethiol, 3-mercaptohexyl acetate, and 3-mercaptohexanol in wine. Optimization of the extraction technique was performed using a two-level fractional factorial design. For the extraction step, the optimum conditions were: Ethylene glycol and silicone coated stir bars, pH at 3.5, sample volume of 25 mL, extraction time of 90 min, NaCl content 4.0 g, and stirring speed at 500 rpm. The optimized method achieved good linearity for all studied compounds (r(2) > 0.995) and it provided detection limits of 21.52, 0.36, 0.73, and 2.55 μg/L for 4-mercapto-4-methylpentan-2-one, 2-furanmethanethiol, 3-mercaptohexyl acetate, and 3-mercaptohexanol, respectively. It was repeatable, with precisions lower than 18% relative standard deviation for both intraday and interday repeatability. The developed procedure is suitable for the determination of these kinds of compounds when they are present at medium concentration levels. It was finally applied to real wine samples with negative aroma derived from the high concentration levels of these compounds.

Analysis of temperature-mediated changes in the wine yeast Saccharomyces bayanus var uvarum. An oenological study of how the protein content influences wine quality.

Saccharomyces bayanus var. uvarum plays an important role in the fermentation of red wine from the D.O. Ribera del Duero. This is due to the special organoleptic taste that this yeast gives the wines and their ability to ferment at low temperature. To determine the molecular factors involved in the fermentation process at low temperature, a differential proteomic approach was performed by using 2D‐DIGE, comparing, qualitatively and quantitatively, the profiles obtained at 13 and 25°C. A total of 152 protein spots were identified. We detected proteins upregulated at 13°C that were shown to be related to temperature stress, the production of aromatic compounds involved in the metabolism of amino acids, and the production of fusel alcohols and their derivatives, each of which is directly related to the quality of the wines. To check the temperature effects, an aromatic analysis by GC–MS was performed. The proteomic and “aromatomic” results are discussed in relation to the oenological properties of S. bayanus var. uvarum.