Circular dipptides in food and drinks (Doctoral thesis)

Μπρατάκος, Σωτήριος Μ.

Diketopiperazines (DKPs) are cyclic dipeptides which have been detected in a variety of natural products, especially in thermally treated or fermented foods and beverages, providing a metallic bitter taste. DKPs, mainly due to their characteristic heterocyclic system, have been reported to exhibit a broad spectrum of biological activities including antimicrobial, antiviral, antitumor, antihyperglycaemic and antimutagenic. The purpose of this study was to develop a liquid chromatography method for separation and identification of DKPs in complex matrices (i.e. food and beverages) as well as a high resolution mass spectrometry method providing accurate full scan MS and MSn data in order to investigate the fragmentation pattern and confirm the chemical formula and structure of DKPs containing aromatic amino acids. Our results which were supported by in silico DFT energy calculations, revealed different and common fragmentation pathways as well as a series of characteristic fragment ions which are representative of the amino acid residues. The role of MSn was signified by the results since it provided a clear picture of the fragmentation cascades. The obtained fragments are diagnostic and could be used to distinguish cyclic dipeptides in different matrices. In the present study, several DKPs were identified in seven different Greek varieties of processed olives using HR-LC-MSn. The identification of DKPs in olive samples was achieved by comparison of their retention time and fragmentation pattern with reference DKP standards. The MSn spectra were identical to confirm the presence of specific compounds because their results associate both fragmentation pattern and fragments’ intensity. Nine compounds were found out of a total of 19 standard DKPs. The most prominent diketopiperazine was the cyclo(Phe-Phe) followed by and cyclo(Phe-Pro). Furthermore, four cyclic dipeptides, 2.5-diketopiperazines (DKPs) were found in fifteen bottled wines produced from different grape varieties. These compounds were detected for the first time in wine, and their chemical identification was achieved through comparison of their physical and chemical data with that obtained through chemical synthesis.
Alternative title / Subtitle: σύνθεση, αναλυτικός προσδιορισμός και ταυτοποίηση της μοριακής δομή τους
composition, determination and identification of molecular species
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
Subject classification: Τρόφιμα
Keywords: Δικετοπιπεραζίνες,Χρωματογραφία,GC-MS,LC-MS,Τρόφιμα,Diketopiperazines,Cromatography,Foods
Appears in Collections:Διδακτορικές Διατριβές

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