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Localização e simulação de som tridimensional

Azevedo, Joaquim Amândio Rodrigues
Fonte: Faculdade de Engenharia da Universidade do Porto Publicador: Faculdade de Engenharia da Universidade do Porto
Tipo: Dissertação de Mestrado
Publicado em //1994 POR
Relevância na Pesquisa
95.54%

The combination of neural estimates in prediction and decision problems

Freitas, Paulo Sérgio Abreu
Fonte: Universidade de Lisboa: Faculdade de Ciências Publicador: Universidade de Lisboa: Faculdade de Ciências
Tipo: Tese de Doutorado
Publicado em //2008 ENG
Relevância na Pesquisa
95.5%
In this dissertation, different ways of combining neural predictive models or neural-based forecasts are discussed. The proposed approaches consider mostly Gaussian radial basis function networks, which can be efficiently identified and estimated through recursive/adaptive methods. Two different ways of combining are explored to get a final estimate – model mixing and model synthesis –, with the aim of obtaining improvements both in terms of efficiency and effectiveness. In the context of model mixing, the usual framework for linearly combining estimates from different models is extended, to deal with the case where the forecast errors from those models are correlated. In the context of model synthesis, and to address the problems raised by heavily nonstationary time series, we propose hybrid dynamic models for more advanced time series forecasting, composed of a dynamic trend regressive model (or, even, a dynamic harmonic regressive model), and a Gaussian radial basis function network. Additionally, using the model mixing procedure, two approaches for decision-making from forecasting models are discussed and compared: either inferring decisions from combined predictive estimates, or combining prescriptive solutions derived from different forecasting models. Finally...

inVídeo: uma aplicação de vídeo interactivo sobre a Internet

Marques, Eduardo Miguel Dias
Fonte: Faculdade de Engenharia da Universidade do Porto Publicador: Faculdade de Engenharia da Universidade do Porto
Tipo: Dissertação de Mestrado
Publicado em //2004 POR
Relevância na Pesquisa
115.56%
A utilização de vídeo e áudio sobre a Internet tem ganho nos últimos anos um interesse crescente. Na verdade, o interesse não é recente, mas os limites tecnológicos de variadíssimas ordens impediam o desenvolvimento e a utilização alargada de aplicações com media ricos. Os avanços nas tecnologias relacionadas com, por exemplo, a compressão, as redes e as ferramentas multimédia possibilitaram o desenvolvimento e o funcionamento, de uma forma alargada, de sistemas multimédia. O trabalho apresentado nesta dissertação descreve a especificação e a implementação de um sistema de formação à distância, designado inVídeo, que utiliza o vídeo como elemento central. O sistema tem como objectivo proporcionar formação por intermédio de uma aplicação que permite a visualização paralela de um vídeo com imagens ou animações, acompanhada com outros dados, como texto e acesso a ficheiros que podem ser descarregados. O enquadramento para esta aplicação surgiu das necessidades de formação contínua de um centro hospitalar, todavia a aplicação foi desenvolvida para poder ser utilizada noutras instituições. A especificação passou pela descrição do problema e sua modelação utilizando um método para o desenvolvimento de aplicações interactivas...

Sensores de pressão em fibra óptica para o estudo dos fenómenos da percolação da água em solos

Freitas, Norberto Bruno Serrão de
Fonte: Universidade da Madeira Publicador: Universidade da Madeira
Tipo: Dissertação de Mestrado
Publicado em 24/01/2013 POR
Relevância na Pesquisa
115.6%
Dada a necessidade de obtermos sistemas monitorizados com elevada precisão, de grande durabilidade e resistentes às condições atmosféricas, surgiu a possibilidade de aplicação das fibras ópticas como sensores para monitorização de pressão. Nesse contexto, as fibras “hetero-core” (fibra óptica composta por uma fibra multimodo entre duas fibras ópticas monomodo) e a utilização de lentes GRIN (“GRaded INdex”) em conjunto com superfícies reflectoras permitem a determinação da pressão e são objecto de estudo desta dissertação. Em termos de aplicação, o objectivo principal desta tese de mestrado foi de proporcionar o projecto e desenvolvimentos da medida de pressão em 48 pontos para um tanque de estudo dos fenómenos de percolação da água nos solos e que é pertencente à Secção de Geotecnia do Departamento de Engenharia Civil da Faculdade de Engenharia da Universidade do Porto. Inicialmente, foi caracterizado um sistema contendo uma fibra “hetero-core” à qual foi aplicada uma curvatura, com auxílio de uma carruagem micrométrica. Este sistema permitiu a simulação do mesmo efeito de aplicação de pressão à fibra “hetero-core”. Na configuração seguinte, usou-se um OTDR (“Optical Time Domain Reflectometer”) para visualização e registo das perdas encontradas durante o processo de dobrar e esticar da fibra “hetero-core”. Ao longo deste registo...

Validação do sistema absoluto para a determinação da massa volúmica de líquidos

Jacinto, Sérgio Miguel Ferreira
Fonte: Faculdade de Ciências e Tecnologia Publicador: Faculdade de Ciências e Tecnologia
Tipo: Dissertação de Mestrado
Publicado em //2012 POR
Relevância na Pesquisa
75.57%
Dissertação para obtenção do Grau de Mestre em Engenharia Mecânica; A metrologia aplica-se a qualquer grandeza determinada. O rigor das dimensões de qualquer peça mecânica é fundamental, sendo que em nenhum processo de fabrico é possível obter as dimensões exatas previamente estabelecidas. Assim antes de qualquer processo de fabrico deve ser conhecida a grandeza do erro tolerável. Para evitar erros no processo de fabrico, deve existir um controlo orientado para o processo, evitando assim a rejeição de produtos fabricados que não respeitem as normas estabelecidas. Na engenharia mecânica, desde a fase de projeto, passando pela precisão e exatidão do processo produtivo, até à manutenção de sistemas, a metrologia é fundamental para garantir a qualidade do serviço. No setor da metalomecânica, qualquer empresa necessita de rigor e exatidão na sua atividade. Assim o Instituto Português da Qualidade é a entidade responsável pela normalização, certificação e metrologia, disseminando a qualidade de produtos e serviços prestados em Portugal. Após aquisição de uma nova célula de medição de massa volúmica de líquidos para substituir a já existente, desgastada devido à utilização e tempo de vida...

Teorias de aprendizagem: pré-concepções de alunos da área de exatas do ensino superior privado da cidade de São Paulo

Gomes,Rolfi Cintas; Costa,Rogério Homem da; Neves,Alexandre Aparecido; Schimiguel,Juliano; Silveira,Ismar Frango; Amaral,Luiz Henrique
Fonte: Programa de Pós-Graduação em Educação para a Ciência, Universidade Estadual Paulista (UNESP), Faculdade de Ciências, campus de Bauru. Publicador: Programa de Pós-Graduação em Educação para a Ciência, Universidade Estadual Paulista (UNESP), Faculdade de Ciências, campus de Bauru.
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 PT
Relevância na Pesquisa
95.65%
Este trabalho busca analisar as preferências de aprendizagem de alunos de cursos superiores na área de Ciências Exatas, de maneira a verificar que aspectos das principais teorias de aprendizagem se tornam mais adequados a este perfil de aluno. Para isso, foram observados os principais elementos das Teorias de Ensino e Aprendizagem Comportamentalista, Construtivista, Sociointeracionista, Racionalista e Significativa, e sintetizados em um formulário de perguntas de múltipla escolha. Foi estudado um grupo de alunos de uma Universidade da cidade São Paulo, sendo 26 alunos do primeiro ano do curso de Ciência da Computação e 22 alunos de Engenharia Mecânica, formando uma população de 48 alunos. Os resultados desta pesquisa são explicitados e algumas considerações a respeito são apresentadas neste artigo.

Solid phase microextraction, mass spectrometry and metabolomic approaches for detection of potential urinary cancer biomarkers: a powerful strategy for breast cancer diagnosis

Silva, Catarina L.; Passos, Mário; Câmara, José S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /01/2012 ENG
Relevância na Pesquisa
75.46%
A sensitive assay to identify volatile organic metabolites (VOMs) as biomarkers that can accurately diagnose the onset of breast cancer using non-invasively collected clinical specimens is ideal for early detection. Therefore the aim of this study was to establish the urinary metabolomic profile of breast cancer patients and healthy individuals (control group) and to explore the VOMs as potential biomarkers in breast cancer diagnosis at early stage. Solid-phase microextraction (SPME) using CAR/PDMS sorbent combined with gas chromatography–mass spectrometry was applied to obtain metabolomic information patterns of 26 breast cancer patients and 21 healthy individuals (controls). A total of seventy-nine VOMs, belonging to distinct chemical classes, were detected and identified in control and breast cancer groups. Ketones and sulfur compounds were the chemical classes with highest contribution for both groups. Results showed that excretion values of 6 VOMs among the total of 79 detected were found to be statistically different (p < 0.05). A significant increase in the peak area of (−)-4-carene, 3-heptanone, 1,2,4-trimethylbenzene, 2-methoxythiophene and phenol, in VOMs of cancer patients relatively to controls was observed. Statiscally significant lower abundances of dimethyl disulfide were found in cancer patients. Bioanalytical data were submitted to multivariate statistics [principal component analysis (PCA)]...

Relationship between antioxidant capacity and total phenolic content of red, rosé and white wines

Paixão, Neuza; Perestrelo, Rosa; Marques, José .; Câmara, José S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /04/2007 ENG
Relevância na Pesquisa
75.46%
Phenolic compounds are one of the most important quality parameters of wines, since they contribute to wine organoleptic characteristics such as colour, astringency, and bitterness. Furthermore, several studies have pointed out that many show biological properties of interest, related to their antioxidant capacity. This antioxidant activity has been thoroughly studied and a wide variety of methods have been developed to evaluate it. In this study, the antioxidant activity of commercial Terras Madeirenses Portuguese wines (Madeira Island) was measured by three different analytical methods: [1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTSradical dot+)) radical cation decolourisation, and ferric reducing/antioxidant power (FRAP) for the evaluation of reducing power (PR) and correlate them with the total phenolic content determined with the Folin–Ciocalteu’s reagent using gallic acid as a standard. The total polyphenol concentration was found to vary from 252 to 1936 mg/l gallic acid equivalents (GAE). The antiradical activity varied from 0.042 to 0.715 mM Trolox equivalents and the antioxidant capacity varied from 344 to 1105 mg/l gallic acid equivalents (GAE). For the reduction power we obtained 3.45–3.86 mM quercetin equivalents.

Comparative study of the whisky aroma profile based on headspace solid phase microextraction using different fibre coatings

Câmara, J. S.; Marques, J. C.; Perestrelo, R. M.; Rodrigues, F.; Oliveira, L.; Andrade, P.; Caldeira, M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /05/2007 ENG
Relevância na Pesquisa
75.46%
A dynamic headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to ion trap mass spectrometry (GC–ITMS) method was developed and applied for the qualitative determination of the volatile compounds present in commercial whisky samples which alcoholic content was previously adjusted to 13% (v/v). Headspace SPME experimental conditions, such as fibre coating, extraction temperature and extraction time, were optimized in order to improve the extraction process. Five different SPME fibres were used in this study, namely, poly(dimethylsiloxane)(PDMS),poly(acrylate)(PA),Carboxen-poly(dimethylsiloxane)(CAR/PDMS),Carbowax-divinylbenzene(CW/DVB)and Carboxen-poly(dimethylsiloxane)-divinylbenzene (CAR/PDMS/DVB). The best results were obtained using a 75 m CAR/PDMS fibre during headspace extraction at 40◦C with stirring at 750rpm for 60min, after saturating the samples with salt. The optimised methodology was then appliedtoinvestigatethevolatilecompositionprofileofthreeScotchwhiskysamples—BlackLabel,BallantinesandHighlandClan.Approximately seventy volatile compounds were identified in the these samples, pertaining at several chemical groups, mainly fatty acids ethyl esters, higher alcohols, fatty acids, carbonyl compounds...

Screening of volatile composition from portuguese multifloral honeys using headspace solid-phase microextraction-gas chromatography–quadrupole mass spectrometry

Pontes, M.; Marques, J. C.; Câmara, J. S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /11/2007 ENG
Relevância na Pesquisa
75.46%
The volatile composition from four types of multifloral Portuguese (produced in Madeira Island) honeys was investigated by a suitable analytical procedure based on dynamic headspace solid-phase microextraction (HS-SPME) followed by thermal desorption gas chromatography–quadrupole mass spectrometry detection (GC–qMS). The performance of five commercially available SPME fibres: 100 μm polydimethylsiloxane, PDMS; 85 μm polyacrylate, PA; 50/30 μm divinylbenzene/carboxen on polydimethylsiloxane, DVB/CAR/PDMS (StableFlex); 75 μm carboxen/polydimethylsiloxane, CAR/PDMS, and 65 μm carbowax/divinylbenzene, CW/DVB; were evaluated and compared. The highest amounts of extract, in terms of the maximum signal obtained for the total volatile composition, were obtained with a DVB/CAR/PDMS coating fibre at 60 °C during an extraction time of 40 min with a constant stirring at 750 rpm, after saturating the sample with NaCl (30%). Using this methodology more than one hundred volatile compounds, belonging to different biosynthetic pathways were identified, including monoterpenols, C13-norisoprenoids, sesquiterpenes, higher alcohols, ethyl esters and fatty acids. The main components of the HS-SPME samples of honey were in average ethanol, hotrienol...

Multivariate analysis for the classification and differentiation of Madeira wines according to main grape varieties

Câmara, J. S.; Alves, M. A.; Marques, J. C.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /02/2006 ENG
Relevância na Pesquisa
85.47%
In order to differentiate and characterize Madeira wines according to main grape varieties, the volatile composition (higher alcohols, fatty acids, ethyl esters and carbonyl compounds) was determined for 36 monovarietal Madeira wine samples elaborated from Boal, Malvazia, Sercial and Verdelho white grape varieties. The study was carried out by headspace solid-phase microextraction technique (HS-SPME), in dynamic mode, coupled with gas chromatography–mass spectrometry (GC–MS). Corrected peak area data for 42 analytes from the above mentioned chemical groups was used for statistical purposes. Principal component analysis (PCA) was applied in order to determine the main sources of variability present in the data sets and to establish the relation between samples (objects) and volatile compounds (variables). The data obtained by GC–MS shows that the most important contributions to the differentiation of Boal wines are benzyl alcohol and (E)-hex-3-en-1-ol. Ethyl octadecanoate, (Z)-hex-3-en-1-ol and benzoic acid are the major contributions in Malvazia wines and 2-methylpropan-1-ol is associated to Sercial wines. Verdelho wines are most correlated with 5-(ethoxymethyl)-furfural, nonanone and cis-9-ethyldecenoate. A 96.4% of prediction ability was obtained by the application of stepwise linear discriminant analysis (SLDA) using the 19 variables that maximise the variance of the initial data set.

Impact of forced-aging process on Madeira Wine flavor

Silva, Hugo Oliveira e; Pinho, Paula Guedes de; Machado, Beatriz P.; Hogg, Tim; Marques, J. C.; Câmara, José S.; Albuquerque, F.; Ferreira, António C. Silva
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Publicado em /11/2008 ENG
Relevância na Pesquisa
85.48%
The aim of this study was to determine the optimal temperature and baking time to obtain a Madeira wine considered typical by an expert panel. For this purpose simultaneous descriptive analyses of typical Madeira wines were performed, and seven descriptors were selected: “dried fruit”, “nutty”, “musty”, “baked”, “oak”, “mushroom”, and “brown sugar”. Up to 10 odor-active zones were the most frequently cited by the members of the GC-olfactometry panel as corresponding to the panel’s descriptors. The odor importance of each of the zones reported by the GC-O analysis was ranked by AEDA. Three odor zones were identified as common to both Malvasia and Sercial wines and had retention indices (RI) of 1993 (“brown sugar” and “toasted”), 2151 (“brown sugar”), and 2174 (“nutty”, “driedfruits”);sotolonwasidentifiedasresponsibleforthislastaroma.Severalmoleculeswereselected to be quantified on baked wines on the basis of AEDA results and expected Maillard volatiles, such as sotolon, furfural, 5-methylfurfural, 5-ethoximethylfurfural, methional, and phenylacetaldehyde. It was observed that typicity scores were positively correlated with the concentrations of sotolon and sugar and baking time and negatively with the fermentation length.

Content in metallic ions of wines from the Madeira and Azores archipelagos

Pérez Trujillo, Juan P.; Conde, José E.; Pérez Pont, Maria L.; Marques, José C.; Câmara, José S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /01/2011 ENG
Relevância na Pesquisa
85.47%
This study determines for the first time Na, K, Ca, Mg, Fe, Cu, Zn, Mn, Sr, Li and Rb contents in wines from the archipelagos of Madeira and Azores (Portugal). The greater part of the mean content for the different parameters fell within the ranges described in the literature, except for sodium whose higher content may be due to the effect of marine spray. ANOVA was used to establish the metals with significant differences in mean content between the wines from both archipelagos, between table and liquor wines of Madeira, and between wines of Pico and Terceira Islands from the Azores archipelago. Principal component analysis shows differences in the wines according to the wine-making process and/or the equipment employed. Stepwise linear discriminant analysis achieves a good classification and validation of wines according to the archipelago of origin, and the island in the case of Azores wines.

Profiling allergic asthma volatile metabolic patterns using a headspace-solid phase microextraction/gas chromatography based methodology

Caldeira, M.; Barros, A. S.; Bilelo, M. J.; Parada, A.; Câmara, J. S.; Rocha, S. M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /06/2011 ENG
Relevância na Pesquisa
85.49%
Allergicasthmarepresentsanimportantpublichealthissuewithsignificantgrowthovertheyears,especially in the paediatric population. Exhaled breath is a non-invasive, easily performed and rapid method forobtainingsamplesfromthelowerrespiratorytract.Inthepresentmanuscript,themetabolicvolatile profiles of allergic asthma and control children were evaluated by headspace solid-phase microextraction combined with gas chromatography–quadrupole mass spectrometry (HS-SPME/GC–qMS). The lack ofstudiesinbreathofallergicasthmaticchildrenbyHS-SPMEledtothedevelopmentofanexperimental design to optimize SPME parameters. To fulfil this objective, three important HS-SPME experimental parameters that influence the extraction efficiency, namely fibre coating, temperature and time extractions were considered. The selected conditions that promoted higher extraction efficiency corresponding to the higher GC peak areas and number of compounds were: DVB/CAR/PDMS coating fibre, 22◦C and 60min as the extraction temperature and time, respectively. The suitability of two containers, 1L Tedlar® bags and BIOVOC®, for breath collection and intra-individual variability were also investigated. The developed methodology was then applied to the analysis of children exhaled breath with allergicasthma(35)...

New method for determination of (E)resveratrol in wine based on microextraction using packed sorbent and ultra-performance liquid chromatography

Gonçalves, João; Câmara, José S.
Fonte: Wiley-VCH Publicador: Wiley-VCH
Tipo: Artigo de Revista Científica
Publicado em /06/2011 ENG
Relevância na Pesquisa
95.48%
An ultra-fast and improved analytical methodology based on microextraction by packed sorbent (MEPS) combined with ultra-performance LC (UPLC) was developed and validated for determination of (E)-resveratrol in wines. Important factors affecting the performance of MEPS such as the type of sorbent material (C2, C8, C18, SIL, and M1), number of extraction cycles, and sample volume were studied. The optimal conditions of MEPS extraction were obtained using C8 sorbent and small sample volumes (50–250mL) in one extraction cycle (extract–discard) and in a short time period (about 3 min for the entire sample preparation step). (E)-Resveratrol was eluted by 1 250mL of the mixture containing 95% methanol and 5% water, and the separation was carried out on a highstrength silica HSS T3 analytical column (100 mm 2.1 mm, 1.8mm particle size) using a binary mobile phase composed of aqueous 0.1% formic acid (eluent A) and methanol (eluent B) in the gradient elution mode (10 min of total analysis). The method was fully validated in terms of linearity, detection (LOD) and quantification (LOQ) limits, extraction yield, accuracy, and inter/intra-day precision, using a Madeira wine sample (ET) spiked with (E)-resveratrol at concentration levels ranging from 5 to 60mg/mL. Validation experiments revealed very good recovery rate of 9575.8% RSD...

Effectiveness of different solid-phase microextraction fibres for differentiation of selected Madeira island fruits based on their volatile metabolite profile: identification of novel compounds

Pereira, João; Pereira, Jorge; Câmara, José S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /01/2011 ENG
Relevância na Pesquisa
85.47%
A headspace solid-phase microextraction (HS-SPME) procedure based on five commercialised fibres (85 μm polyacrylate – PA, 100 μm polydimethylsiloxane – PDMS, 65 μm polydimethylsiloxane/divinylbenzene – PDMS/DVB, 70 μm carbowax/divinylbenzene – CW/DVB and 85 μm carboxen/polydimethylsiloxane – CAR/PDMS) is presented for the characterization of the volatile metabolite profile of four selected Madeira island fruit species, lemon (Citrus limon), kiwi (Actinidia deliciosa), papaya (Carica papaya L.) and Chickasaw plum (Prunus angustifolia). The isolation of metabolites was followed by thermal desorption gas chromatography–quadrupole mass spectrometry (GC–qMS) methodology. The performance of the target fibres was evaluated and compared. The SPME fibre coated with CW/DVB afforded the highest extraction efficiency in kiwi and papaya pulps, while in lemon and plum the same was achieved with PMDS/DVB fibre. This procedure allowed for the identification of 80 compounds, 41 in kiwi, 24 in plums, 23 in papaya and 20 in lemon. Considering the best extraction conditions, the most abundant volatiles identified in kiwi were the intense aldehydes and ethyl esters such as (E)-2-hexenal and ethyl butyrate, while in Chicasaw plum predominate 2-hexenal...

Contribuições da análise textual dos discursos para o ensino em ambientes virtuais; Contributions of the textual analysis of speeches for the teaching in the virtual enviroments

Marquesi, Sueli Cristina
Fonte: Universidade de São Paulo. Faculdade de Filosofia, Letras e Ciências Humanas Publicador: Universidade de São Paulo. Faculdade de Filosofia, Letras e Ciências Humanas
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Formato: application/pdf
Publicado em 16/12/2013 POR
Relevância na Pesquisa
75.55%
O presente artigo tem por objetivo principal discutir aspectos teóricos da Análise Textual dos Discursos que orientam uma metodologia de aprendizagem autônoma por alunos universitários. Tomando por base, principalmente, estudos desenvolvidos por Adam (2008), será discutida uma unidade temática de conteúdo teórico da área de Ciências Exatas, em que sequências explicativas e descritivas constroem-se de forma a proporcionar a interação entre o texto veiculado em ambiente virtual e o aluno e, consequentemente, facilitam-lhe a aprendizagem de um conteúdo totalmente novo. Para tanto, trar-se-á para a discussão atividades destinadas a alunos de Engenharia de uma universidade brasileira, componentes de uma disciplina trabalhada a distância. A metodologia em discussão estabelece o diálogo entre uma questão central do ensino em ambientes virtuais de aprendizagem – a interação pela linguagem – e o papel que o aluno, nesses ambientes, assume: um leitor/autor que constrói sentidos e transfere conhecimentos.; The present paper aims at discussing theoretical aspects of Textual Analysis of Speeches which guide an autonomous learning methodology for university students. Having as a theoretical ground, mainly, the studies developed by Adam (2008)...

Solid phase microextraction as a reliable alternative to conventional extraction techniques to evaluate the pattern of hydrolytically released components in Vitis vinifera L. grapes

Perestrelo, Rosa; Caldeira, Michael; Câmara, José S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /06/2012 ENG
Relevância na Pesquisa
85.48%
In present research, headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–qMS), was evaluated as a reliable and improved alternative to the commonly used liquid–liquid extraction (LLE) technique for the establishment of the pattern of hydrolytically released components of 7 Vitis vinifera L. grape varieties, commonly used to produce the world-famous Madeira wine. Since there is no data available on their glycosidic fractions, at a first step, two hydrolyse procedures, acid and enzymatic, were carried out using Boal grapes as matrix. Several parameters susceptible of influencing the hydrolytic process were studied. The best results, expressed as GC peak area, number of identified components and reproducibility, were obtained using ProZym M with b-glucosidase activity at 35 °C for 42 h. For the extraction of hydrolytically released components, HS-SPME technique was evaluated as a reliable and improved alternative to the conventional extraction technique, LLE (ethyl acetate). HS-SPME using DVB/CAR/PDMS as coating fiber displayed an extraction capacity two fold higher than LLE (ethyl acetate). The hydrolyzed fraction was mainly characterized by the occurrence of aliphatic and aromatic alcohols...

Characterization of volatile substances in apples from rosaceae family by headspace solid‐phase microextraction followed by GC‐qMS

Ferreira, Liseth; Perestrelo, Rosa; Caldeira, Michael; Câmara, José S.
Fonte: WILEY-VCH Verlag GmbH & Co. KGaA Publicador: WILEY-VCH Verlag GmbH & Co. KGaA
Tipo: Artigo de Revista Científica
Publicado em /03/2009 ENG
Relevância na Pesquisa
85.49%
The volatile composition of different apple varieties of Malus domestica Borkh. species from different geographic regions at Madeira Islands, namely Ponta do Pargo (PP), Porto Santo (PS), and Santo da Serra (SS) was established by headspace solid-phase microextraction (HS-SPME) procedure followed by GC-MS (GC-qMS) analysis. Significant parameters affecting sorption process such as fiber coating, extraction temperature,extractiontime,sampleamount,dilutionfactor,ionicstrength,anddesorption time,wereoptimizedanddiscussed.TheSPMEfibercoatedwith50/30 lmdivinylbenzene/carboxen/PDMS (DVB/CAR/PDMS) afforded highest extraction efficiency of volatile compounds, providing the best sensitivity for the target volatiles, particularly whenthesampleswereextractedat508Cfor30 minwithconstantmagneticstirring. A qualitative and semi-quantitative analysis between the investigated apple species has been established. It was possible to identify about 100 of volatile compounds amongpulp(46,45,and39),peel(64,60,and64),andentirefruit(65,43,and50)inPP, PS,andSSapples,respectively.Ethylesters,terpenes,andhigheralcoholswerefound tobethemostrepresentativevolatiles. a-Farnesene,hexan-1-olandhexyl2-methylbutyratewerethecompoundsfoundinthevolatileprofileofstudiedappleswiththelargestGCarea...

Optimisation of stir bar sorptive extraction and liquid desorption combined with large volume injection-gas chromatography–quadrupole mass spectrometry for the determination of volatile compounds in wines

Coelho, Elisabete; Perestrelo, Rosa; Neng, Nuno R.; Câmara, José S.; Coimbra, Manuel A.; Nogueira, J. M. F.; Rocha, Sílvia M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /06/2008 ENG
Relevância na Pesquisa
85.48%
Stir bar sorptive extraction and liquid desorption followed by large volume injection coupled to gas chromatography–quadrupole mass spectrometry (SBSE–LD/LVI-GC–qMS) had been applied for the determination of volatiles in wines. The methodology was optimised in terms of extraction time and influence of ethanol in the matrix; LD conditions, and instrumental settings. The optimisation was carried out by using 10 standards representative of the main chemical families of wine, i.e. guaiazulene, E,E-farnesol, β-ionone, geranylacetone, ethyl decanoate, β-citronellol, 2-phenylethanol, linalool, hexyl acetate and hexanol. The methodology shows good linearity over the concentration range tested, with correlation coefficients higher than 0.9821, a good reproducibility was attained (8.9–17.8%), and low detection limits were achieved for nine volatile compounds (0.05–9.09 μg L−1), with the exception of 2-phenylethanol due to low recovery by SBSE. The analytical ability of the SBSE–LD/LVI-GC–qMS methodology was tested in real matrices, such as sparkling and table wines using analytical curves prepared by using the 10 standards where each one was applied to quantify the structurally related compounds. This methodology allowed, in a single run...