Remedios Castro

Removal of iron, copper and manganese from white wines through ion exchange techniques: effects on their organoleptic characteristics and susceptibility to browning

Abstract Ion exchange techniques have been used to reduce the content of iron, copper and manganese in white wines. Two exchanger resins have been compared, a chelating resin, the active group of which is iminodiacetate and a Dowex, acidic cation exchange resin. The results obtained show that the technique of using exchanger resins is extremely effective in lowering the metal content of wines, although on occasions, their use alters the organoleptic characteristics of the wine. Treated wines present lower polyphenolic and aromatic profiles than the untreated wines. Polyphenolic and metallic reductions would explain why treated wines present a notably reduced susceptibility to browning.

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.

Influence of metallic content of fino sherry wine on its susceptibility to browning

Abstract A study has been conducted on the influence of the content of copper, iron, and manganese on the tendency of a “fino” sherry wine to undergo browning. The concentrations considered cover the ranges found for these metals in this type of wine. The content in copper does not seem to have a significant influence on the susceptibility to browning of “fino” sherry wines. In respect to iron, which does influence this process, there are no significant differences in concentrations ranging from 3 to 9 mg/l. For manganese no differences are observed for concentrations ranging from 0.8 to 1.6 mg/l, but concentrations of manganese below 0.8 mg/l prevent the increase in iron content from being translated into an increased susceptibility to browning.

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.

Development of a stir bar sorptive extraction method for the determination of volatile compounds in orange juices.

A stir bar sorptive extraction method for the determination of volatile compounds in orange juices was developed. The extraction variables were optimized using a reduced two-level factorial screening design (2(5-1) ), and the most suitable analytical conditions for the extraction of the studied compounds were: sample volume 10 mL, extraction time 60 min, stirring speed 1800 rpm, NaCl amount 30% (weight/volume), and twister length 10 mm. The optimized method was further validated, obtaining good linearity and detection and quantification limits low enough to correctly determine the studied compounds. As well, for most of the studied compounds precision and recovery values were good. Several orange juice samples (squeezed and commercial) were extracted following the optimized extraction method and analyzed by gas chromatography coupled to mass spectrometry detection. The method has proven to be suitable for the determination of the aroma of orange juice, of which limonene was the major volatile compound in all the studied samples.

Effects of Grape Destemming on the Polyphenolic and Volatile Content of Fino Sherry Wine during Alcoholic Fermentation

This study has been conducted to explore the influence of different degrees of destemming on the polyphenolic and volatile content of wines from the Palomino finogrape variety. Wines obtained from destemmed grape did not present reduced polyphenolic content. No relationship was observed between degrees of destemming and changes in the polyphenolic content. Destemming prior to pressing did not modify the production of volatile compounds during fermentation and wines with similar organoleptic characteristics to those without destemming were obtained.

Characterization by gas chromatography-olfactometry of the most odour-active compounds in Italian balsamic vinegars with geographical indication

Odour-active compounds in three traditional balsamic vinegars from Modena (TB) and seven balsamic vinegars from Modena (PGI) were determined by gas chromatography-olfactometry (GC-O) using frequency of detection methodology (modified frequency, MF, %). The main odour compounds (mean MF > 60%) were 2,3-butanedione (75%), acetic acid (70%), furan-2-carbaldehyde (62%), 1-(furan-2-yl)ethanone (62%), 2-methylpropanoic acid (66%), butanoic acid (78%), 3-methylbutanoic acid (83%), 2-phenylethyl acetate (65%), 2-hydroxy-3-methylcyclopent-2-en-1-one (61%), 2-phenylethan-1-ol (84%), 3-hydroxy-2-methylpyran-4-one (60%), (5-formylfuran-2-yl)methyl acetate (68%), 2-phenylacetic acid (69%) and 4-hydroxy-3-methoxybenzaldehyde (86%). All odour impact compounds were grouped into 7 categories according to their aromatic character: cheesy-butter-lactic, sweet, flower, empyreumatic, fruity, chemical and miscellaneous. Balsamic vinegars from Modena showed lower values for the sweet category whereas for the miscellaneous and chemical categories they exhibited higher values than those found in traditional balsamic vinegars from Modena. A principal component analysis showed that both types of vinegars from Modena could be clearly differentiated based on olfactometric data.

Optimization of a multiple headspace sorptive extraction method coupled to gas chromatography-mass spectrometry for the determination of volatile compounds in macroalgae

A novel extraction technique is proposed in which the Multiple Headspace Extraction (MHE) approach is used in conjunction with Headspace Sorptive Extraction (HSSE) and Gas Chromatography-Mass Spectrometry (GC-MS) detection. The extraction method was developed to determine volatile compounds in macroalgae. Optimization of the extraction parameters was carried out using design of experiments to identify factors that affect the extraction: extraction time, temperature, twister length and amount of sample. The results of the optimization led to an extraction of 2 g of sample using a 20 mm Twister® at 66 °C for 180 min. The progression constants (β) were calculated for 43 volatile compounds, 29 of which could be quantified using the method. Linearity was attained with a determination coefficient higher than 0.99 for all studied compounds. Inter-day and inter-twister precisions ranged from 0.22% to 19.01% and from 0.69% to 14.76% respectively, and values below 10% were obtained for the majority of compounds. LOD and LOQ values ranged from the values obtained for diethyl succinate (0.012 μg/L and 0.088 μg/L, respectively) and those obtained for dimethyl sulfide (5.544 μg/L and 40.286 μg/L, respectively). However, for the majority of compounds values obtained were below 1 μg/L (LOD) and 5 μg/L (LOQ). Compounds such as ethyl acetate, hexanal, heptadecane, 2-hexenal, 6-methyl-5-hepten-2-one, dimethyl sulfide, benzyl alcohol, beta ionone, or beta cyclocitral, among others were correctly determined in three species of macroalgae: Ulva sp., Gracillaria sp. and Enteromorpha sp.