Browsing by Author "Oliveira, Carla M."
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- Development of a potentiometric method To measure the resistance to oxidation of white wines and the antioxidant power of their constituentsPublication . Oliveira, Carla M.; Ferreira, António C. Silva; Pinho, Paula Guedes de; Hogg, TimThis work describes a new potentiometric method to evaluate the resistance to oxidation of white wines. Reduction and oxidation titrations were made, and coefficient of variation obtained were 10.87 and 2.65%, respectively. The antioxidant powers of ascorbic acid (Aas) and sulfur dioxide (SO2) were evaluated by this method, SO2 proving to be much less active in this respect than ascorbic acid. The two agents did not demonstrate any antioxidant synergy. A relationship between oxygen present and ascorbic acid was found by the proposed method (1 mmol of O2 S 0.84 mmol of Aas). This method enables the distinction of different wines on the basis of their resistance to oxidation
- New qualitative approach in the characterization of antioxidants in white Wines by antioxidant free radical scavenging and NMR techniquesPublication . Oliveira, Carla M.; Ferreira, António C. S.; Pinho, Paula Guedes de; Silva, Artur M. S.The aim of this study was to obtain new information on antioxidant compounds in white wines. For this purpose, white wine degradation was promoted by a forced aged protocol, and six normally aged white wines from different vintages were analyzed. Both normal and forced aged wines were sequentially extracted using hexane and ethyl acetate. Apolar antioxidants were removed using hexane, and polar antioxidants were extracted with ethyl acetate. This last residue was subject to partial re-extraction with hexane and acetone. The antioxidant capacity of the wines and of each fraction was evaluated by two free radical methods, ABTS and DPPH. Normal aging provides a decrease in the total antioxidant capacity of wines. The antioxidant activity of ethyl acetate/acetone extracts was approximately 95% higher than that found for the hexane extracts. Concerning the forced aged wines, results showed that the wine submitted to a temperature of 60 °C for 21 days had higher antioxidant activity than that submitted to a temperature of 20 °C. With regard to the ethyl acetate/acetone extracts, oxygen and temperature treatment leads to a decrease in their antioxidant activity. NMR analysis was performed in the highest antioxidant capacity organic fractions (ethyl acetate/ acetone extracts) and in the aqueous fraction of the control wine (T ) 20 °C), in order to attempt the characterization of species involved in oxygen protection. Possible structures of antioxidant compounds in white wines were proposed. Two of these are tyrosol-like structures. This molecule is a wellknown phenolic compound in wine, and it is reported to have antioxidative effects.
- Oxidation management of white wines using cyclic voltammetry and multivariate process monitoringPublication . Martins, Rui C.; Oliveira, Raquel; Bento, Fatima; Geraldo, Dulce; Lopes, Vitor V.; Pinho, Paula Guedes de; Oliveira, Carla M.; Ferreira, António C. SilvaThe development of a fingerprinting strategy capable to evaluate the “oxidation status” of white wines based on cyclic voltammetry is proposed here. It is known that the levels of specific antioxidants and redox mechanisms may be evaluated by cyclic voltammetry. This electrochemical technique was applied on two sets of samples. One group was composed of normal aged white wines and a second group obtained from a white wine forced aging protocol with different oxygen, SO2, pH, and temperature regimens. A study of antioxidant additions, namely ascorbic acid, was also made in order to establish a statistical link between voltammogram fingerprints and chemical antioxidant substances. It was observed that the oxidation curve presented typical features, which enables sample discrimination according to age, oxygen consumption, and antioxidant additions. In fact, it was possible to place the results into four significant orthogonal directions, compressing 99.8% of nonrandom features. Attempts were made to make voltammogram fingerprinting a tool for monitoring oxidation management. For this purpose, a supervised multivariate control chart was developed using a control sample as reference. When white wines are plotted onto the chart, it is possible to monitor the oxidation status and to diagnose the effects of oxygen regimes and antioxidant activity. Finally, quantification of substances implicated in the oxidation process as reagents (antioxidants) and products (off-flavors)was tried using a supervised algorithmic the partial least square regression analysis. Good correlations (r > 0.93) were observed for ascorbic acid, Folin-Ciocalteu index, total SO2, methional, and phenylacetaldehyde. These results show that cyclic voltammetry fingerprinting can be used to monitor and diagnose the effects of wine oxidation.
- 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.
- Saccharomyces cerevisiae oxidative response evaluation by cyclic voltammetry and gas chromatography−mass spectrometryPublication . Castro, Cristiana C.; Gunning, Caitriona; Oliveira, Carla M.; Couto, José A.; Teixeira, José A.; Martins, Rui C.; Ferreira, António C. SilvaThis study is focused on the evaluation of the impact of Saccharomyces cerevisiae metabolism in the profile of compounds with antioxidant capacity in a synthetic wine during fermentation. A bioanalytical pipeline, which allows for biological systems fingerprinting and sample classification by combining electrochemical features with biochemical background, is proposed. To achieve this objective, alcoholic fermentations of a minimal medium supplemented with phenolic acids were evaluated daily during 11 days, for electrochemical profile, phenolic acids, and the volatile fermentation fraction, using cyclic voltametry, high-performance liquid chromatography−diode array detection, and headspace/solid-phase microextraction/gas chromatography−mass spectrometry (target and nontarget approaches), respectively. It was found that acetic acid, 2- phenylethanol, and isoamyl acetate are compounds with a significative contribution for samples metabolic variability, and the electrochemical features demonstrated redox-potential changes throughout the alcoholic fermentations, showing at the end a similar pattern to normal wines. Moreover, S. cerevisiae had the capacity of producing chlorogenic acid in the supplemented medium fermentation from simple precursors present in the minimal medium.
- A simple ultraperformance liquid chromatography mass spectrometry method for the determination of cortisol level in sea bass plasmaPublication . Oliveira, Carla M.; Campos, Inês; Vidigal, Susana S. M. P.; Pintado, Manuela E.; Oliveira, Catarina S. S.A simple, precise, and rapid ultra-performance liquid chromatography method for cortisol quantification in sea bass plasma, based on LC-ESI-UHR-QqTOF-MS, was optimised using tolperisone as internal standard. Sea bass plasma samples containing cortisol were spiked with tolperisone as internal standard and extracted with acetonitrile. Samples were vortexed and centrifuged at 15,000g for 10 min at 4 °C. The final extract, diluted in ammonium formate (1:1), was injected in the LC-ESI-UHR-QqTOF-MS system for analysis. Mass spectrometry acquisition parameters were set using positive ionisation mode over a m/z range from 150 to 2200. Cortisol and tolperisone were detected and quantified at m/z 363.21 and 246.18, respectively, in an Auto MS (MS/MS) mode. The detection and quantification limits of cortisol in sea bass plasma were 0.01 and 0.02 μg/mL, respectively. The mean extraction recovery of cortisol was of 99.1 ± 4.0 %. The within- and between-day precision presents a relative standard deviation (RSD) below 2.9 % and 5.3, respectively. Furthermore, the effect of four different diets (fish feed 1–4) in the basal and stress-induced plasma cortisol levels of sea bass was also assessed.