| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 1.94 MB | Adobe PDF |
Advisor(s)
Abstract(s)
O objectivo deste trabalho residiu na comparaĆ§Ć£o da capacidade antioxidativa de diferentes compostos fenĆ³licos. Os estudos foram efectuados com base na avaliaĆ§Ć£o da temperatura de induĆ§Ć£o de oxidaĆ§Ć£o do Ć”cido linoleico. No inĆcio do trabalho realizou-se o estudo da estabilidade tĆ©rmica e termo-oxidativa do Ć”cido linoleico e dos diversos antioxidantes: Ć”cidos protocatecuico e homo-protocatecuico e dos Ć©steres metĆlico, etĆlico e propĆlico do Ć”cido protocatecuico. A estabilidade tĆ©rmica foi estudada desde os 25ĀŗC atĆ© aos 400ĀŗC, em atmosfera de azoto e a estabilidade termo-oxidativa foi avaliada desde os 25ĀŗC atĆ© aos 220ĀŗC, em atmosfera de oxigĆ©nio. Depois de estudar e optimizar as condiƧƵes de anĆ”lise e o mĆ©todo de preparaĆ§Ć£o das amostras, foi analisada a oxidaĆ§Ć£o do Ć”cido linoleico na presenƧa dos antioxidantes mencionados. Os resultados obtidos mostraram que, em comparaĆ§Ć£o com os Ć©steres, os compostos Ć”cidos sĆ£o antioxidantes mais eficazes. Nos Ć”cidos observa-se que a introduĆ§Ć£o de um grupo CH2 entre o anel aromĆ”tico e o grupo Ć”cido aumenta a eficĆ”cia do poder antioxidante da espĆ©cie quĆmica. No respeitante ao poder estabilizante dos esteres do Ć”cido protocatecuico, o aumento do nĆŗmero de Ć”tomos de carbono do radical do grupo Ć©ster tem um efeito difĆcil de caracterizar no que concerne Ć capacidade antioxidativa. O Ć©ster com o maior radical (radical propilo) tem mais capacidade para evitar o aumento da velocidade de oxidaĆ§Ć£o medida pelo pico do termograma diferencial, mas ao mesmo tempo a temperatura de induĆ§Ć£o de oxidaĆ§Ć£o indica que o Ć©ster com maior radical apresenta menor capacidade para estabilizar o Ć”cido linoleico. Foi, ainda estudado o efeito que a concentraĆ§Ć£o do antioxidante e o mĆ©todo de preparaĆ§Ć£o das amostras tinham na estabilidade do Ć”cido linoleico. No caso dos Ć”cidos verificou-se que o aumento para o dobro da concentraĆ§Ć£o do antioxidante resultava num aumento em 21ĀŗC da temperatura de induĆ§Ć£o da oxidaĆ§Ć£o. Avaliou-se, tambĆ©m, a utilizaĆ§Ć£o de termogramas diferenciais para a caracterizaĆ§Ć£o da acĆ§Ć£o antioxidativa.
The aim of this work was to compare the anti-oxidative capacity of different phenolic compounds. The study has been based on the evaluation of linoleic acid oxidation induction temperature. In the beginning of the work, the thermal and thermo-oxidative stability of linoleic acid and the different antioxidants was determined: protochatechuic acid, homoprotochatechuic acid, and methylic, ethylic and propylic esters of protochatechuic acid. The thermal stability was analyzed from 25ĀŗC to 400ĀŗC, in nitrogen atmosphere, while thermo-oxidative stability was evaluated from 25ĀŗC to 220ĀŗC, in oxygen atmosphere. After studying and optimizing the analysis conditions and the sample preparation method, the linoleic acid oxidation in the presence of the different antioxidants was evaluated. The results showed that acids seem to be more efficient when compared with esters. Was demonstrated that, in acids, a CH2 group between the aromatic ring and the acid group increases the anti-oxidative power of the chemical species. Among the esters of protochatechuic acid, itās difficult to characterize the effect of increasing the carbon atom number (of the radical of ester group) on the antioxidative capacity. The propylic ester, which is the longer one, exhibited a better capacity to avoid the increase of oxidation speed, when measured the peak temperature of the differential thermogram. But, simultaneously, the oxidation induction temperature indicates that the ester with longer radical shows less capacity to stabilize the linoleic acid. The effect that the concentration and the sample preparation method had on the linoleic acid stability was investigated. Phenolic acids showed that the increase for the double of concentration resulted in the improvement of 21ĀŗC on the oxidation induction temperature. The use of differential thermograms for the characterization of antioxidative action was evaluated in this work.
The aim of this work was to compare the anti-oxidative capacity of different phenolic compounds. The study has been based on the evaluation of linoleic acid oxidation induction temperature. In the beginning of the work, the thermal and thermo-oxidative stability of linoleic acid and the different antioxidants was determined: protochatechuic acid, homoprotochatechuic acid, and methylic, ethylic and propylic esters of protochatechuic acid. The thermal stability was analyzed from 25ĀŗC to 400ĀŗC, in nitrogen atmosphere, while thermo-oxidative stability was evaluated from 25ĀŗC to 220ĀŗC, in oxygen atmosphere. After studying and optimizing the analysis conditions and the sample preparation method, the linoleic acid oxidation in the presence of the different antioxidants was evaluated. The results showed that acids seem to be more efficient when compared with esters. Was demonstrated that, in acids, a CH2 group between the aromatic ring and the acid group increases the anti-oxidative power of the chemical species. Among the esters of protochatechuic acid, itās difficult to characterize the effect of increasing the carbon atom number (of the radical of ester group) on the antioxidative capacity. The propylic ester, which is the longer one, exhibited a better capacity to avoid the increase of oxidation speed, when measured the peak temperature of the differential thermogram. But, simultaneously, the oxidation induction temperature indicates that the ester with longer radical shows less capacity to stabilize the linoleic acid. The effect that the concentration and the sample preparation method had on the linoleic acid stability was investigated. Phenolic acids showed that the increase for the double of concentration resulted in the improvement of 21ĀŗC on the oxidation induction temperature. The use of differential thermograms for the characterization of antioxidative action was evaluated in this work.
Description
Mestrado em Engenharia QuĆmica
Keywords
Antioxidantes fenĆ³licos Temperatura de induĆ§Ć£o da oxidaĆ§Ć£o Calorimetria diferencial de varrimento
Citation
Publisher
Instituto PolitƩcnico do Porto. Instituto Superior de Engenharia do Porto