Remedios Castro Mejías

Optimisation of headspace solid-phase microextraction for the analysis of volatile phenols in wine

Headspace solid-phase microextraction has been applied to the analysis of volatile phenols in wine. Silica fibre coated with Carbowax-divinylbenzene was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, polyacrylate, carboxen-polydimethylsiloxane, and polydimethylsiloxane-divinylbenzene. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength and sample volume were optimised using a two-level factorial design expanded further to a central composite design, in order to evaluate several possibly influential and/or interacting factors. The headspace (HS)-SPME procedure developed shows adequate detection and quantitation limits, and linear ranges for correctly analysing these compounds in wine. The recoveries obtained were close to 100%, with repeatability values lower than 16%. The method was applied to a variety of white and red wines.

Optimisation of headspace solid-phase microextraction for analysis of aromatic compounds in vinegar.

Abstract Headspace solid-phase microextraction has been applied to the analysis of aroma compounds in vinegar. Silica fibre coated with Carboxen–polydimethylsiloxane was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, Carbowax–divinylbenzene, and polydimethylsiloxane–divinylbenzene, but its repeatability was low. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength, and sample volume were optimised using a two-level factorial design expanded further to a central composite design. This chemometric tool is very appropriate in screening experiments where the aim is to investigate several possibly influential and/or interacting factors. The extraction efficiency is inversely affected by the acetic acid content—an increase in the acetic acid concentration decreases the extraction efficiency. No interference is observed with the increase in content of polyphenols.

Headspace solid-phase microextraction analysis of aroma compounds in vinegar. Validation study.

Headspace solid-phase microextraction (HS-SPME) was evaluated for analysing aromatic compounds in vinegar. The fibre used (a Carboxen-polydimethylsiloxane fibre), and the analytical conditions had been optimised in a previous work. The HS-SPME procedure developed shows detection and quantitation limits, and linear ranges adequate for analysing this type of compounds. The recoveries obtained were close to 100%, with repeatability values lower than 20%. However, considerable differences have been detected between different fibres. The method was applied to a variety of Sherry wine vinegars.

A new FT-IR method combined with multivariate analysis for the classification of vinegars from different raw materials and production processes.

BACKGROUND Due to the diversity of vinegars on the market and the increase in demand, it is considered necessary to investigate and establish criteria for classifying them in order to obtain more information concerning their real origin. New spectroscopic techniques such us mid-infrared spectroscopy with Fourier transform (FT-IR) are capable of providing information in relation to these aspects. FT-IR combined with multivariate analysis has been used to classify vinegars according to the raw materials and production processes (with or without ageing in wood). Principal component analysis (PCA), partial least-squares discriminant analysis regression (PLS-DA) and stepwise linear discriminant analysis (SLDA) were used. RESULTS The results obtained have been compared to those achieved using different analytical parameters (polyphenolic content, organic acids and volatile compounds). SLDA and PLS-DA results show the ability of mid-FT-IR spectra to discriminate among vinegars from different raw materials and with or without ageing in wood, with correct classification percentages similar to those obtained using different analytical parameters. CONCLUSION The discriminative ability combined with other advantages (e.g. rapid and non-destructive analysis, low cost) makes this new FT-IR method a promising tool for the classification and/or differentiation of vinegars.

Characterization and Differentiation of Sherry Brandies Using Their Aromatic Profile

Aroma compounds of 48 Sherry brandies have been identified and quantified by the stir bar sorptive extraction method coupled to gas chromatography-mass spectrometry (SBSE-GC/MS). Analysis of variance and multivariate analysis techniques have been used to classify these brandy samples according to the commercial category (Solera brandy, Solera Reserva brandy, and Solera Gran Reserva brandy). From an univariate point of view (analysis of variance), several of the volatile compounds considered showed significant differences. Principal component analysis, using the global data matrix, showed that only the Solera brandy samples, with the shortest aging in wood, were well-differentiated from the others. Partial least-squares discriminant analysis (PLS-DA) results provided evidence of the ability of the content of volatile compounds to discriminate among the different commercial categories. Linear discriminate analysis allowed for a 93% differentiation according to the commercial category and, thus, the length of its aging process in wood. The results obtained show that it would be possible to ensure the commercial category of a Sherry brandy using its content of volatile compounds.

Traceability of phytosanitary products in the production of a Sherry wine vinegar.

In the present work, the monitoring of the evolution of the different phytosanitary products employed in the production of a Sherry wine vinegar has been carried out. The study covers the complete process, from the grape ripening to the vinegar fermentation. For the liquid sample analysis, a method based on SBSE (stir bar sorptive extraction) coupled to GC-MS and previously developed was used. For the grape samples, the use of two different extraction methods (ultrasound assisted extraction and microwave assisted extraction) was considered. Both methods were correctly optimized by means of factorial designs and were finally compared to each other. Considering the obtained results, the ultrasound extraction method was chosen to make the extraction of the solid samples. After the extraction process, the different extracts were analyzed by means of SBSE-GC-MS. The achieved results show the decrease of the phytosanitary product residues during the grape ripening, most of them being removed completely before the final product.