Browsing by Author "Freitas, Victor de"
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- Development and optimization of a HS-SPME-GC-MS methodology to quantify volatile carbonyl compounds in Port winesPublication . Moreira, Nathalie; Araújo, Ana Margarida; Rogerson, Frank; Vasconcelos, Isabel; Freitas, Victor de; Pinho, Paula Guedes deA method based on headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-triple quadrupole/mass spectrometry detection (GC-TQ/MS) with a prior derivatization step with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was developed to quantify carbonyl compounds in different categories of Port wines. Optimal extraction conditions were obtained incubating 2 ml of wine with 2.3 g/l of PFBHA for 10 min and extracted during 20 min at 32 °C. The method was validated for 38 carbonyl compounds (alkanals, alkenals, Strecker aldehydes, dialdehydes, ketones and furan aldehydes) with regard to linearity, repeatability, inter and intra-day precision and accuracy, showing that the method is suitable for the determination of carbonyl compounds in wines. Tawny wines with ‘indication of age’ (10–40 years old) presented the highest levels of some carbonyl compounds, such as propanal, pentanal, hexanal, Strecker aldehydes, diacetyl, methyl glyoxal, 3-pentanone and 2-furfural, whereas Ruby wines were characterized by the highest amounts of some unidentified compounds.
- Experimental design, modeling, and optimization of high-pressure-assisted extraction of bioactive compounds from pomegranate peelPublication . Alexandre, Elisabete M. C.; Araújo, Paula; Duarte, Maria F.; Freitas, Victor de; Pintado, Manuela; Saraiva, Jorge A.Pomegranate peels are very rich in bioactive compounds, particularly antioxidants, that when properly extracted, may be used for different applications such as food, cosmetics, and pharmaceutics. In this paper, we studied the effect of high-pressure extraction on antioxidant activity and bioactive compounds (total phenolics, tannins, flavonoids, and anthocyanins) of pomegranate peel, using a Box-Behnken design to evaluate the effects of pressure, extraction time, and ethanol concentration to estimate the optimum extraction conditions by response surface methodology (RSM). Individual phenolics, tannins, and anthocyanins were also identified and quantified using the optimum extraction conditions identified by RSM. The results indicated that a quadratic polynomial model could be used to optimize high-pressure extraction of bioactive compounds from pomegranate peel (R (2) higher than 0.90). Ethanol concentration was the variable with higher impact and high pressure increased in average 13% the extraction amount of bioactive compounds. The optimum extraction conditions were similar for all compounds (except for anthocyanins) ranging between 356 and 600 MPa, 32 and 56% of ethanol, and 30 min of extraction time. A pressure of 492 MPa, extraction time of 30 min, and an ethanol concentration of 37% were found to result in the highest amount of the quantified individual compounds. Analysis of variance indicated a high goodness of fit of the used models and adequacy of response surface methodology for optimizing high-pressure extraction. The pomegranate peels are industrial by-products that are rich in bioactive compounds and the results obtained in this work show that high pressure is a promising process for scale up of extraction processes. However, pilot plant tests at higher scale will be necessary to ponder the economic viability of the process.
- High-pressure assisted extraction of bioactive compounds from industrial fermented fig by-productPublication . Alexandre, Elisabete M. C.; Araújo, Paula; Duarte, Maria F.; Freitas, Victor de; Pintado, Manuela; Saraiva, Jorge A.High-pressure assisted extraction was employed to obtain fig by-product derived extracts and its impact was evaluated on antioxidant activity and total phenolic, tannin, and flavonoid. A Box-Behnken design was applied to evaluate the effects of pressure, extraction time and ethanol concentration on extractions and optimal conditions were estimated by response surface methodology. The correlation analysis of the mathematical-regression model indicated that a quadratic polynomial model could be employed to optimize the high pressure extraction of compounds. Only the models developed for total antioxidant activity by DPPH · and for total flavonoids presented coefficient determinations lower than 0.95. From response surface plots, pressure, extraction time and ethanol concentration showed independent and interactive effects. The optimal conditions included 600 MPa, an extraction time between 18 and 29 min, depending on the parameter analyzed and a low ethanol concentration (<15%) except for flavonoids (48%). High pressure led to an increase of 8-13% of antioxidant activity and an increase of 8-11% of total phenolics, flavonoids and tannins content when compared to extracts performed at 0.1 MPa. Analysis of variance indicated a high goodness of fit of the models used and the adequacy of response surface methodology for optimizing high pressure extraction.
- Oxidation mechanisms occurring in winesPublication . Oliveira, Carla Maria; Ferreira, António César Silva; Freitas, Victor de; Silva, Artur M. S.The present review aims to show the state of the art on the oxidation mechanisms occurring in wines, as well as the methods to monitor, classify and diagnose wine oxidation. Wine oxidation can be divided in enzymatic oxidation and non-enzymatic oxidation. Enzymatic oxidation almost entirely occurs in grape must and is largely correlated with the content of hydroxycinnamates, such as caffeoyltartaric acid and para-coumaroyltartaric acid, and flavan-3-ols. Non-enzymatic oxidation, also called chemical oxidation of wine, prevails in fermented wine and begin by the oxidation of polyphenols containing a catechol or a galloyl group. These phenolic. reactions, both enzymatic and non-enzymatic, result in by-products named quinones. However, in non-enzymatic oxidation, oxygen does not react directly with phenolic compounds. The limitation on the reactivity of triplet oxygen is overcome by the stepwise addition of a single electron, which can be provided by reduced transition metal ions, essentially iron(II) and copper(I). The sequential electron transfer leads to the formation of hydroperoxide radical (HOO center dot), hydrogen peroxide (H2O2), and hydroxyl radical (HO center dot). The later radical will oxidize almost any organic molecule found in wine and will react with the first species it encounters, depending on their concentration. Sulfur dioxide (SO2) and ascorbic acid, when added to wine, are able to reduce the quinones. Alternative options have been assessed for the prevention of oxidation during wine storage; nevertheless, these are not fully understood or commonly accepted. During aging, aldehydes are important intermediates in the chemical transformations occurring in wines, leading to color and flavor changes. In the same way, a range of off-flavors can be formed from wine oxidation. At low concentrations these flavors may add to the complexity of a wine, but as these increase they begin to detract from wine quality. In addition to the major chemical browning involving wine phenols, the main oxidation reactions occurring during grape juice heating or storage are caramelization and Maillard reaction, which are temperature dependent. Different methods have been proposed in the literature, addressing the complexity and multi-scale related with the oxidation process, to attempt the quantification of antioxidant activity in wines. These methods can be broadly divided in: i) methods based on chemical reactions and ii) methods based on the chemical-physical properties of antioxidants.
- Type 2 Diabetes mellitus alters the cargo of (poly)phenol metabolome and the oxidative status in circulating lipoproteinsPublication . Reis, Ana; Rocha, Sara; Dias, Irundika HK.; Costa, Raquel; Soares, Raquel; Sánchez-Quesada, José Luis; Perez, Antonio; Freitas, Victor deThe incidence of diabetes on the worldwide population has tripled in the past 5 decades. While drug-based therapies are valuable strategies to treat and ease the socio-economic burden of diabetes, nutritional strategies offer valuable alternatives to prevent and manage diabetes onset and contribute to the sustainability of health budgets. Whilst, intervention studies have shown that (poly)phenol-rich diets improve fasting glucose levels and other blood parameters, very little is known about the distribution of ingested polyphenols in circulation and the impact of diabetes on its cargo. In this study we investigate the impact of type 2 diabetes on the cargo of plasma (poly)phenols. Our results show that phenolic compounds are heterogeneously distributed in circulation though mainly transported by lipoprotein populations. We also found that diabetes has a marked effect on the phenolic content transported by VLDL resulting in the decrease in the content of flavonoids and consequently a decrease in the antioxidant capacity. In addition to the reduced bioavailability of (poly)phenol metabolites and increase of oxidative status in LDL and HDL populations in diabetes, cell-based assays show that sub-micromolar amounts of microbial (poly)phenol metabolites are able to counteract the pro-inflammatory status in glucose-challenged endothelial cells. Our findings highlight the relevance of triglyceride-rich lipoproteins in the transport and delivery of bioactive plant-based compounds to the endothelium in T2DM supporting the adoption of nutritional guidelines as an alternative strategy to drug-based therapeutic approaches.