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Aplicações de novas metodologias analíticas no estudo de compostos fenólicos em matrizes alimentares
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O crescente interesse no estudo dos compostos fenólicos, particularmente os ácidos fenólicos, deve-se às propriedades antioxidantes que evidenciam, acreditando-se que possam desempenhar um importante papel na prevenção de doenças cardiovasculares e do cancro. Neste sentido, é de todo o interesse o desenvolvimento de métodos analíticos capazes de determinar e quantificar os compostos fenólicos numa vasta gama de alimentos. O presente trabalho consistiu no desenvolvimento, optimização, validação e aplicação de um novo método para a determinação de ácidos fenólicos (clorogénico, ferúlico, p-cumárico e cafeíco) em produtos alimentares, recorrendo à micro-extracção adsortiva em barra com dessorção líquida, seguida de análise por electroforese capilar com detecção por rede de díodos (BAμE-LD/CE-DAD). Numa primeira abordagem, seleccionou-se o material adsorvente mais adequado para a extracção dos ácidos fenólicos, nomeadamente carvão activado, polidimetilsiloxano, co-polímero de divenilbenzeno e alguns dos seus derivados, tendo o derivado de co-polímero de divenilbenzeno com propriedades de troca aniónica e fase reversa (Oásis® MAX Sorbent) demonstrado ser o mais eficaz. Para optimização da metodologia desenvolvida (BAμE (MAX)-LD/CE-DAD), foram efectuados estudos sistemáticos a diversos parâmetros, tendo 3 h de extracção (1000 rpm; pH 6) e o uso de solução metanol/ácido fórmico (2 %) durante 15 min para retro-extracção, permitido obter recuperações compreendidas entre 35 e 40 %. O método revelou ainda, excelente linearidade (r2 > 0,99) na gama compreendida entre 0,8 e 8,0 mg/L, tendo-se alcançado limites de detecção e de quantificação entre 18 - 82 μg/L e 61 - 273 μg/L, respectivamente. Com recurso ao método da adição de padrão, a aplicação da presente metodologia a matrizes alimentares, nomeadamente chá verde, mel e sumo de frutos vermelhos, demonstrou bom desempenho analítico tendo-se verificado a ocorrência de níveis de alguns dos ácidos fenólicos estudados. A metodologia proposta (BAμE(MAX)-LD/CE-DAD), apresentou como principais vantagens a utilização de pequenas quantidades de amostra e solventes, tempo analítico reduzido e fácil manipulação, associada à rapidez, simplicidade e bom desempenho analítico.
The increasing interest in the study of phenolic compounds, particularly the phenolic acids, is due to their antioxidant properties as they play a very important role in the prevention of cardiovascular diseases and in cancer. Therefore, it is very important the development of analytical methods for the determination and quantification of phenolic compounds in a wide range of food products. The present work consisted in the development, optimization, validation and application of a new method for the determination of four phenolic acids (chlorogenic, ferulic, p-coumaric and caffeic) in food stuffs, using bar adsorptive micro-extraction and liquid desorption, followed by capillary electrophoresis with diode array detection (BAμE-LD/CE-DAD). In a first approach, several adsorbent materials more suitable for the extraction of the studied compounds were selected, namely activated carbon, polydimethylsiloxane, divinylbenzene co-polymer and its derivatives, where the anionic exchange and reverse-phase divinylbenzene co-polymer derivative (Oásis® MAX Sorbent) showed much better efficacy. To optimize the developed methodology (BAμE(MAX)-LD/CE-DAD), systematic studies were carried out for the different experimental variables, in which 3 h of extraction (1000 rpm; pH 6) and a solution of methanol/formic acid (2 %) for back-extraction during 15 min, allowing recovery yields of the studied compounds in between 35 and 40 %. This method also presented excellent linearity (r2 > 0.99) ranging from 0.8 to 8.0 mg/L, reaching limits of detection and quantification in between 18 - 82 μg/L and 61 - 273 μg/L, respectively. By using the standard addition methodology, the application of the method to food matrices, in particular green tea, honey and red fruit juices, demonstrated good performance leading to the quantification of levels of the studied compounds. The proposed methodology (BAμE(MAX)-LD/CE-DAD), presented several advantages, namely small amounts of sample and solvents used, reduced analytical time and easy manipulation, associated to a fast, simple and remarkable analytical performance.
The increasing interest in the study of phenolic compounds, particularly the phenolic acids, is due to their antioxidant properties as they play a very important role in the prevention of cardiovascular diseases and in cancer. Therefore, it is very important the development of analytical methods for the determination and quantification of phenolic compounds in a wide range of food products. The present work consisted in the development, optimization, validation and application of a new method for the determination of four phenolic acids (chlorogenic, ferulic, p-coumaric and caffeic) in food stuffs, using bar adsorptive micro-extraction and liquid desorption, followed by capillary electrophoresis with diode array detection (BAμE-LD/CE-DAD). In a first approach, several adsorbent materials more suitable for the extraction of the studied compounds were selected, namely activated carbon, polydimethylsiloxane, divinylbenzene co-polymer and its derivatives, where the anionic exchange and reverse-phase divinylbenzene co-polymer derivative (Oásis® MAX Sorbent) showed much better efficacy. To optimize the developed methodology (BAμE(MAX)-LD/CE-DAD), systematic studies were carried out for the different experimental variables, in which 3 h of extraction (1000 rpm; pH 6) and a solution of methanol/formic acid (2 %) for back-extraction during 15 min, allowing recovery yields of the studied compounds in between 35 and 40 %. This method also presented excellent linearity (r2 > 0.99) ranging from 0.8 to 8.0 mg/L, reaching limits of detection and quantification in between 18 - 82 μg/L and 61 - 273 μg/L, respectively. By using the standard addition methodology, the application of the method to food matrices, in particular green tea, honey and red fruit juices, demonstrated good performance leading to the quantification of levels of the studied compounds. The proposed methodology (BAμE(MAX)-LD/CE-DAD), presented several advantages, namely small amounts of sample and solvents used, reduced analytical time and easy manipulation, associated to a fast, simple and remarkable analytical performance.
Descrição
Tese de mestrado, Química, Universidade de Lisboa, Faculdade de Ciências, 2009
Palavras-chave
Micro-extracção adsortiva em barra (BAμE) Ácidos fenólicos Electroforese capilar (CE) Chá verde Mel Sumo de frutos vermelhos Teses de mestrado - 2009