Exploring the capabilities of gas chromatography and liquid chromatography single and tandem mass spectrometry for discriminating and characterizing marine oils by using chemometric tools

• Autor(a) principal: Zeng, Yingxu
• Data de Publicação: 2010
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/10736
• topic: Gas chromatography; Liquid chromatography; Marine oils; Domínio/Área Científica::Engenharia e Tecnologia

Assessing the capabilities of instrumental techniques for discriminating marine oils and studying the positional distribution of fatty acids on the backbone of triacylglycerols (TAG) are of vital importance from commercial, nutritional, biochemical and technological points of view. This represents a great challenge for analysts due to the wide variety of fatty acids and the complexity of naturally occurring TAG species. In this thesis, the potential of gas chromatography (GC) for discriminating full fatty acid methyl ester (FAME) profiles of marine oils (cod liver, salmon, seal and whale oils) is evaluated by means of principal component analysis (PCA). The FAME profiles from plant oils such as rapeseed, linseed and soy oils and seven different brands of omega-3 (ω-3) fatty acids supplements are also used in the discrimination process. The results from the PCA plots can reliably distinguish between plant, ω-3 fatty acids supplements, fish and marine mammal oils. By removing the contribution of the ω-3 fatty acids supplements and plant oils, it is possible to discriminate within every type of fish and marine animal oils. GC offers a rapid, simple and convenient means of discriminating marine oils from different species, brands and grades. The thesis also studies the feasibility of fingerprinting and discriminating marine oils based on their TAG profiles using liquid chromatography electrospray single and tandem mass spectrometry (LC-ESI-MS and LC-ESI-MS2) in conjunction with chemometric tools. Four kinds of profiles, including total ion chromatogram (TIC) and mass spectral profiles derived from LC-ESI-MS and LC-ESI-MS2 experiments, are examined prior to data pretreatment by component detection algorithm (CODA) to reduce the noise and background. These profiles are subsequently subjected to PCA to evaluate their performance for discriminating marine oils and plant oils. The results show that the TIC profiles derived from both LC-ESI-MS and LC-ESI-MS2 experiments turn out to be inadequate for discrimination of complex marine oils. Although the classification results are remarkably improved by using single mass spectral profiles derived from LC-ESI-MS experiments, the differentiation among seal oils of different species and qualities is not achieved. In comparison, the use of tandem mass spectral profiles from LC-ESI-MS2 experiment is demonstrated to be the best strategy for discrimination of marine oils which enables the differentiation not only between marine oils and plant oils but also among the seal oils of different species and qualities. The tandem mass spectral profiles could preferably represent the characteristics of TAG patterns, and could be used as an alternative approach for fingerprinting and detecting of adulteration of marine oils. The final aspect studied in the present thesis is the structural characterization of TAG by using LC-ESI-MS2 for identifying the positional distribution of fatty acids on the glycerol backbone in cod liver oil. A computational algorithm is developed to characterize rapidly and interpret automatically the mass spectra of the various detected TAG species. Three different solvent mixtures are used to dissolve the sample prior to the instrumental analysis. The discrepancies between the results indicate that the choice of the solvent system influences the identification of the TAG species. The results obtained by the proposed LC-ESI-MS2 approach are in agreement with those from the well established lipase method. LC-ESI-MS2 provides a suitable and powerful strategy for the structural characterization of TAG in cod liver oil.