Paulo J. Magalhães
University of Porto
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Featured researches published by Paulo J. Magalhães.
Journal of Chromatography A | 2010
Paulo J. Magalhães; Joana Vieira; Luís Moreira Gonçalves; João Grosso Pacheco; Luís F. Guido; Aquiles A. Barros
The aim of the present work was the development of a suitable methodology for the separation and determination of phenolic compounds in the hop plant. The developed methodology was based on the sample purification by adsorption of phenolic compounds from the matrix to polyvinylpolypyrrolidone (PVPP) and subsequent desorption of the adsorbed polyphenols with acetone/water (70:30, v/v). At last, the extract was analyzed by HPLC-DAD and HPLC-ESI-MS/MS. The first phase of this work consisted of the study of the adsorption behavior of several classes of phenolic compounds (e.g. phenolic acids, flavonols, and flavanols) by PVPP in model solutions. It has been observed that the process of adsorption of the different phenolic compounds to PVPP (at low concentrations) is differentiated, depending on the structure of the compound (number of OH groups, aromatic rings, and stereochemistry hindrance). For example, within the phenolic acids class (benzoic, p-hydroxybenzoic, protocatechuic and gallic acids) the PVPP adsorption increases with the number of OH groups of the phenolic compound. On the other hand, the derivatization of OH groups (methylation and glycosylation) resulted in a greatly diminished binding. The use of PVPP revealed to be very efficient for adsorption of several phenolic compounds such as catechin, epicatechin, xanthohumol and quercetin, since high adsorption and recovery values were obtained. The methodology was further applied for the extraction and isolation of phenolic compounds from hops. With this methodology, it was possible to obtain high adsorption values (>or=80%) and recovery yield values (>or=70%) for the most important phenolic compounds from hops such as xanthohumol, catechin, epicatechin, quercetin and kaempferol glycosides, and in addition it allows the identification of about 30 phenolic compounds by HPLC-DAD and HPLC-ESI-MS/MS.
Journal of Chromatography A | 2010
Luís Moreira Gonçalves; Paulo J. Magalhães; Inês Maria Valente; João Grosso Pacheco; Pavel Dostálek; David Sýkora; José A. Rodrigues; Aquiles A. Barros
In this work, a recently developed extraction technique for sample preparation aiming the analysis of volatile and semi-volatile compounds named gas-diffusion microextraction (GDME) is applied in the chromatographic analysis of aldehydes in beer. Aldehydes-namely acetaldehyde (AA), methylpropanal (MA) and furfural (FA)-were simultaneously extracted and derivatized with 2,4-dinitrophenylhydrazine (DNPH), then the derivatives were separated and analyzed by high-performance liquid chromatography with spectrophotometric detection (HPLC-UV). The identity of the eluted compounds was confirmed by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass-spectrometry detection in the negative ion mode (HPLC-APCI-MS). The developed methodology showed good repeatability (ca. 5%) and linearity as well as good limits of detection (AA-12.3, FA-1.5 and MA 5.4microgL(-1)) and quantification (AA-41, FA-4.9 and MA 18microgL(-1)); it also appears to be competitive in terms of speed and cost of analysis.
Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment | 2010
Luís Moreira Gonçalves; João Grosso Pacheco; Paulo J. Magalhães; José A. Rodrigues; Aquiles A. Barros
An automated flow injection analysis (FIA) system, based on an initial analyte separation by gas-diffusion and subsequent determination by square-wave voltammetry (SWV) in a flow cell, was developed for the determination of total and free sulfur dioxide (SO2) in wine. The proposed method was compared with two iodometric methodologies (the Ripper method and a simplified method commonly used by the wine industry). The developed method displayed good repeatability (RSD lower than 6%) and linearity (between 10 and 250 mg l−1) as well as a suitable LOD (3 mg l−1) and LOQ (9 mg l−1). A major advantage of this system is that SO2 is directly detected by flow SWV.
Journal of Natural Products | 2013
Raquel Costa; Rita Negrão; Inês Maria Valente; Ângela Castela; Delfim Duarte; Luísa Guardão; Paulo J. Magalhães; José A. Rodrigues; João Tiago Guimarães; Pedro Gomes; Raquel Soares
Type 1 diabetes mellitus is responsible for metabolic dysfunction, accompanied by chronic inflammation, oxidative stress, and endothelium dysfunction, and is often associated with impaired wound healing. Phenol-rich food improves vascular function, contributing to diabetes prevention. This study has evaluated the effect of phenol-rich beverage consumption in diabetic rats on wound healing, through angiogenesis, inflammation, and oxidative stress modulation. A wound-healing assay was performed in streptozotocin-induced diabetic Wistar rats drinking water, 5% ethanol, and stout beer with and without 10 mg/L xanthohumol (1), for a five-week period. Wounded skin microvessel density was reduced to normal values upon consumption of 1 in diabetic rats, being accompanied by decreased serum VEGF-A and inflammatory markers (IL-1β, NO, N-acetylglucosaminidase). Systemic glutathione and kidney and liver H2O2, 3-nitrotyrosine, and protein carbonylation also decreased to healthy levels after treatment with 1, implying an improvement in oxidative stress status. These findings suggest that consumption of xanthohumol (1) by diabetic animals consistently decreases inflammation and oxidative stress, allowing neovascularization control and improving diabetic wound healing.
Talanta | 2010
João Grosso Pacheco; Inês Maria Valente; Luís Moreira Gonçalves; Paulo J. Magalhães; José A. Rodrigues; Aquiles A. Barros
A membraneless extraction module (MLEM) for the sample preparation of volatile compounds and its use for the chromatographic analysis of vicinal diketones in beer are reported. The extraction process is based on the same principles of gas diffusion (GD) and pervaporation (PV); however it does not use a membrane. This module has a lower chamber where the sample continuously flows, while volatile compounds evaporate to the headspace. Inside the module there is a suspended small reactor, where a small volume of a suitable acceptor solution is placed. This extraction module was tested in the determination of vicinal diketones (VDKs) in beer (CV=5%; LOD=4 microg L(-1)), showing applicability with real samples. Several parameters of the extraction process, such as temperature, sample flow and extraction time, were studied and optimized. This module proved to be a good tool for the sampling of volatile compounds, since the extraction is made without using a membrane avoiding all the robustness problems related with its use.
Acta Horticulturae | 2013
Paulo J. Magalhães; Luís Moreira Gonçalves; Luís F. Guido; Mrša Vladimir; T Kincl; Tomáš Brányik; Pavel Dostálek
Xanthohumol, a prenylated chalcone from hops and beer, is a phenolic compound that has received considerable attention in recent years. This compound has a range of interesting biological properties that may have therapeutic utility: anti-inflammatory, antioxidant, antilipoperoxidative activities as well as antiangiogenic, antiproliferative and apoptotic effects, mainly assessed in vitro studies that reasonably suggest a potential chemopreventive activity. Phenomenon how xanthohumol affects brewing yeast’s metabolism, yeast viability and vitality were studied during the production of a xanthohumol enriched beer (10 mg/L xanthohumol). The results showed that yeast viability was slightly decreased by xanthohumol, but on the other hand yeast vitality in the xanthohumol enriched brewing trials was slightly better. The content of higher alcohols and esters was similar to the control in all the xanthohumol enriched brewing trials. In laboratory scale experiment about effect of xanthohumol on brewing yeast growing was done. No effect of xanthohumol on yeast growth was detected. Due to the fact that yeast viability was slightly decreased by xanthohumol, experiment with zymolyase was done. Yeast cells cultivated with xanthohumol are significantly more sensitive to zymolyase treatment.
Natural Product Communications | 2009
Paulo J. Magalhães; Daniel O. Carvalho; J.M. Cruz; Luís F. Guido; Aquiles A. Barros
Journal of Chromatography A | 2007
Paulo J. Magalhães; Luís F. Guido; José M. Cruz; Aquiles A. Barros
Journal of The Institute of Brewing | 2008
Paulo J. Magalhães; Pavel Dostálek; José M. Cruz; Luís F. Guido; Aquiles A. Barros
Food Research International | 2011
Paulo J. Magalhães; Suzete M. Almeida; Ana R.M. Carvalho; Luís Moreira Gonçalves; João Grosso Pacheco; J.M. Cruz; Luís F. Guido; Aquiles A. Barros