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- Study of quinones reactions with wine nucleophiles by cyclic voltammetryPublication . Oliveira, Carla. M.; Barros, António S.; Ferreira, António César Silva; Silva, Artur M. S.Quinones are electrophilic species which can react with various nucleophiles, like wine antioxidants, such as sulfur dioxide or ascorbic acid, thiols, amino acids, and numerous polyphenols. These reactions are very important in wine aging because they mediate oxygen reactions during both production and bottle aging phases. In this work, the major challenge was to determine the interaction between ortho-quinones and wine nucleophiles (amino acids, thiols, and the antioxidants SO2 and ascorbic acid), by cyclic voltammetry. Wine-model solutions with gallic acid, caffeic acid, or (+)-catechin and nucleophilic compounds were used. To understand the effect of nucleophilic addition in wine, a white wine with the same added nucleophiles was also analysed. Cyclic voltammograms were taken with glassy carbon electrode or screen-printed carbon electrodes, respectively, for wine-model and white wines solutions, in the absence and in the presence of nucleophiles. A nucleophilic order profile related to the cathodic current intensity decrease was observed.
- Wine oxidation profile accessed by voltammetric, antioxidant scavenging and GC-MS techniquesPublication . Oliveira, Carla Maria; Silva, Artur M. S.; Barros, António S.; Silva Ferreira, António César
- Phenolic compounds in wine: primary substrates for oxidationPublication . Oliveira, Carla Maria; Silva, Artur M. S.; Barros, António S.; Silva Ferreira, António César
- Quantification of 3-deoxyglucosone (3DG) as an aging marker in natural and forced aged winesPublication . Oliveira, Carla M.; Santos, Sónia A. O.; Silvestre, Armando J. D.; Barros, António S.; Ferreira, António César S.; Silva, Artur M. S.The Maillard reaction product 3-deoxyglucosone (3DG) was quantified in wines, by high-performance liquid chromatography-mass spectrometry analysis after derivatization with ortho-phenylenediamine. Both sweet red Port wines and dry white wines were analysed during natural and forced aging. In natural aging, and for dry white wines, 3DG is negatively correlated to age (r = −0.939), while for sweet red Port wines, 3DG is positively correlated to age (r = 0.782). The same tendency was observed during a wine forced aging protocol. For a dry white wine, with higher levels of α-amino acids, 3DG is consumed (kconsumption 0.077–0.098 day−1) along the time protocol, while for a sweet red Port wine, with lower levels of α-amino acids, an accumulation of 3DG is observed with time (kformation 0.041–0.060 day−1). These results suggest that 3DG content can be used as an aging marker, as it has discriminated dry white and sweet red Port wines from different ages and cultivars. Analysis of wine-model solutions allowed verifying that the fructose content has a higher effect on 3DG formation than glucose, as well as that an increase on amino acids content does not lead to an increase of 3DG yields.
- Quinones as Strecker degradation reagents in wine oxidation processesPublication . Oliveira, Carla Maria; Santos, Sónia A. O.; Silvestre, Armando J. D.; Barros, António S.; Ferreira, António César Silva; Silva, Artur M. S.The Strecker aldehydes formed during the reaction between α-amino acids (phenylalanine or methionine) and either gallic acid, caffeic acid or (+)-catechin ortho-quinones were evaluated in wine-model systems. It was demonstrated that phenylacetaldehyde was formed by quinone intermediates at wine pH. The highest amounts of phenylacetaldehyde during the 10days of experiment (69±5µg/L/day; 7x>Control) were obtained from (+) catechin, followed by gallic acid (61±4µg/L/day; 6x>Control) and caffeic acid (41±4µg/L/day; 4x>Control). The intermediate structures delivered from the reaction of ortho-quinones with α-amino acids were demonstrated by MSn.
- Influence of the temperature and oxygen exposure in red Port wine: a kinetic approachPublication . Oliveira, Carla Maria; Barros, António S.; Ferreira, António César Silva; Silva, Artur M. S.Although phenolics are recognized to be related with health benefits by limiting lipid oxidation, in wine, they are the primary substrates for oxidation resulting in the quinone by-products with the participation of transition metal ions. Nevertheless, high quality Port wines require a period of aging in either bottle or barrels. During this time, a modification of sensory properties of wines such as the decrease of astringency or the stabilization of color is recognized to phenolic compounds, mainly attributed to anthocyanins and derived pigments. The present work aims to illustrate the oxidation of red Port wine based on its phenolic composition by the effect of both thermal and oxygen exposures. A kinetic approach toanthocyanins degradation was also achieved. For this purpose a forced red Port wine aging protocol was performed at four different storage temperatures, respectively, 20, 30, 35 and 40 degrees C, and two adjusted oxygen saturation levels, no oxygen addition (treatment I), and oxygen addition (treatment II). Three hydroxycinnamic esters, three hydroxycinnamic acids, three hydroxybenzoic acids, two flavan-3-ols, and six anthocyanins were quantitated weekly during 63 days, along with oxygen consumption. The most relevant phenolic oxidation markers were anthocyanins and catechin-type flavonoids, which had the highest decreases during the thermal and oxidative red Port wine process. Both temperature and oxygen treatments affected the rate of phenolic degradation. In addition, temperature seems to influence mostly the phenolics kinetic degradation.
- Evaluation of beer deterioration by gas chromatography–mass spectrometry/multivariate analysis: a rapid tool for assessing beer compositionPublication . Rodrigues, João A.; Barros, António S.; Carvalho, Beatriz; Brandão, Tiago; Gil, Ana M.; Ferreira, António C. SilvaBeer stability is a major concern for the brewing industry, as beer characteristics may be subject to significant changes during storage. This paper describes a novel non-targeted methodology for monitoring the chemical changes occurring in a lager beer exposed to accelerated aging (induced by thermal treatment: 18 days at 45 degrees C), using gas chromatography-mass spectrometry in tandem with multivariate analysis (GC-MS/MVA). Optimization of the chromatographic run was performed, achieving a threefold reduction of the chromatographic time. Although losing optimum resolution, rapid GC runs showed similar chromatographic profiles and semi-quantitative ability to characterize volatile compounds. To evaluate the variations on the global volatile signature (chromatographic profile and m/z pattern of fragmentation in each scan) of beer during thermal deterioration, a non-supervised multivariate analysis method, Principal Component Analysis (PCA), was applied to the GC-MS data. This methodology allowed not only the rapid identification of the degree of deterioration affecting beer, but also the identification of specific compounds of relevance to the thermal deterioration process of beer, both well established markers such as 5-hydroxymethylfufural (5-HMF), furfural and diethyl succinate, as well as other compounds, to our knowledge, newly correlated to beer aging.