Caracterización de compuestos fenólicos en matrices vegetales del alto consumo mediante técnicas analíticas avanzadas

Resumen

SUMMARY This doctoral thesis, entitled ¿Characterization of phenolic compounds in highly consumed vegetables matrices by using advanced analytical techniques¿, consists of two main sections: the Introduction and the Experimental Section. The first section offers an overview of the Mediterranean diet and its key foods (mainly fruits and vegetables) and their importance as highly-consumed plant foods and also as good sources of bioactive compounds and phytochemicals, with a special focus on the phenolic compounds. Finally, the analytical tools used to characterize phenolic compounds are described, including high-performance liquid chromatography (HPLC) and ultra-high-performance liquid chromatography (UPLC) coupled to different detectors such as UV-visible (UV-vis) and electrospray ionization (ESI) mass spectrometry (MS) with time-of-flight (TOF) and quadrupole time-of-flight (QTOF) analyzers, are described. The experimental section is divided in five chapters as follows: Chapter 1 demonstrates a powerful analytical method to separate and characterize the phytochemical compounds in whole pods of three cultivars of green bean (Phaseolus vulgaris). Fresh green beans, the immature pods of any type of common beans, are very low in calories and contain no saturated fat. Nevertheless, this vegetable is a very good source of vitamins, minerals, and plant-derived phytochemicals. In this sense, an extraction method has been used to isolate the phytochemical compounds from the study sample using an aqueous-methanolic solvent, followed by HPLC separation coupled to TOF-MS. The proposed method characterized a total of 72 phytochemical compounds, 54 being reported in green beans for the first time, by using the retention time, the data generated by TOF-MS, and the literature. The cultivar Strike was found to be richer in flavonoids compared to other cultivars analyzed. Chapter 2 Cucumber (Cucumis sativus L.), a highly consumed crop, is rich in phenolic compounds. Due to the low amount of data on cucumber, concerning to these compounds, a simple and rapid method to characterize the phenolic compounds present in an extract of the edible part using HPLC¿ESI-QTOF-MS was developed. Thus, based on the accuracy mass data together with the fragmentation pattern, the full scan run generated by QTOF-MS proved to be a useful tool for tentatively characterizing 73 phenolic compounds in the extract of the matrix studied, marking the first comprehensive characterization of phenolic compounds in cucumber. Chapter 3 describes a comprehensive characterization of phenolic and other phytochemical compounds in an extract of the edible part of watermelon which is a highly cultivated and consumed fruit especially in summer times. Thus, the use of HPLC-ESI-QTOF-MS was useful to detect 71 phenolic compounds from different families such as phenolic acids, flavonoids, iridoids, coumarins and lignan using the MS and MS/MS data provided by the QTOF-MS, together with the data taken from the relevant literature on the same botanical family. In addition, watermelon flesh was shown to contain an array of diverse phytochemical components. This is the first report available to characterize individual phenolic and other phytochemical compounds in watermelon. Chapter 4 concerns the characterization of an extract of artichoke (Cynara scolymus) using of HPLC-DAD-ESI-QTOF-MS as a separation and detection method in negative ionization mode. Artichoke is low in calories and fat, but is a rich source of dietary fiber, vitamins, minerals and antioxidant phenolic compounds. Thus, the proposed analytical technique has proven to be useful to characterize 61 phenolic and other polar compounds, 33 being phenolic compounds with their isomers, which have been tentatively characterized in artichoke for the first time, namely: 3 hydroxybenzoic acids, 17 hydroxycinnamic acids, 4 lignans, 7 flavones, 2 flavonols, and one phenol derivative. Furthermore, a total of 28 isomers of previously described phenolics have also been detected. Finally, chapter 5 shows a deep comprehensive profiling of the ¿non-targeted¿ phytochemical compounds present in the hydro-methanolic extract of three cultivars of lettuce, namely, baby, romaine, and iceberg. Thus, an UPLC-ESI-QTOF-MS method was used as a powerful tool to ensure the wide detection of phytochemical compounds from different families with highly deviating properties. In this sense, the proposed method tentatively characterized a total 171 compounds belonging to various structural classes, many of which are reported for the first time in lettuce, phenolics being the most abundant compounds among the phytochemicals characterized.