doktorska disertacija
Valentina Metličar (Author), Alen Albreht (Mentor), Helena Prosen (Thesis defence commission member), Bojana Boh (Thesis defence commission member), Ester Heath (Thesis defence commission member)

Abstract

V okviru doktorskega dela smo identificirali in kvantificirali karotenoide v ekstraktih listov v različnih rastnih fazah dveh invazivnih tujerodnih rastlinskih vrst – japonski dresnik (Fallopia japonica Houtt) in češki dresnik (Fallopia x bohemica). Karotenoidni profili so bili za obe rastlinski vrsti zelo podobni. Ugotovili smo, da se količina prostih ksantofilov in karotenov v jesensko obarvanih listih bistveno zmanjša, po drugi strani pa smo pokazali, da se pojavijo nove ksantofilne spojine – ksantofilni estri maščobnih kislin. Zeleni listi obeh preučevanih dresnikov predstavljajo bogat in trajnosten naravni vir bioaktivnih karotenoidov, predvsem β-karotena (69–97 mg/100g s.m.) in prostega luteina (97–144 mg/100g s.m.), ki bi jih lahko uporabili za pripravo prehranskih dopolnil. Obstaja pa težava. Ker so karotenoidi izven rastlinske matrice zelo nestabilni in v prisotnosti povišane temperature, svetlobe, oksidantov, kislin ali kovin hitro razpadejo, je njihova uporaba omejena. Navdih za reševanje tega problema smo dobili s posnemanjem naravnih procesov, namreč, estrenje fotosintetskih ksantofilov naj bi v jeseni med drugim povečalo njihovo kemijsko stabilnost. V ta namen smo razvili prvo okolju prijazno in ekonomsko upravičljivo sintetsko platformo, kjer smo uporabili zelene, GRAS in obnovljive reagente ter topila. V β-pinenu kot reakcijskem topilu in pri sobni temperaturi ter atmosferskem tlaku smo s kombinacijo 5 modelnih ksantofilov in 11 strukturno in elektronsko različnih kislinskih anhidridov pripravili 55 različnih ksantofilnih estrov. Pokazali smo, da se estrenje lahko izvede tudi brez topila in z uporabo ekstrakta odpadnega rastlinskega materiala zelenih listov japonskega dresnika in olupkov avokada, ki predstavljata bogat obnovljiv vir luteina oziroma anteraksantina. Sintetizirane spojine smo očistili in jih okarakterizirali na podlagi podatkov pridobljenih s pomočjo HPLC-PDA-MSn in HRMS. Od 55 spojin jih je bilo 22 prvič uspešno sintetiziranih. Uspešnost povečanja kemijske stabilnosti ksantofilov preko estrenja smo preverili na 13 različnih luteinskih diestrih, ki smo jih sintetizirali bodisi iz čistega luteina bodisi iz ekstrakta zelenih listov japonskega dresnika. Vsak luteinski diester smo ločeno izpostavili posameznemu stresnemu pogoju: povišani temperaturi (60 °C), svetlobi (UV-A), oksidantu (H2O2) in kislemu okolju. Na podlagi sistematične stabilnostne študije smo prvi pokazali povezavo med kemijsko stabilnostjo, kemijsko strukturo in okoljem luteinskih estrov, v katerem se nahajajo. Od vseh pripravljenih estrov so se za najbolj obetavne izkazali lutein di(2,2-dimetilpropanoat), lutein di(2-metilpropanoat) in lutein di(3- metilbutanoat), saj so bili, ne glede na izbrani stresni pogoj, 1,4–20-krat bolj stabilni v primerjavi s prostim luteinom. Ugotovili smo, da lahko matrica rastlinskega ekstrakta močno vpliva na stabilnost ksantofilov (pozitivno ali negativno), odvisno od stresnega pogoja in tipa estra. Listi japonskega dresnika torej predstavljajo odpadek, ki na trajnosten način omogoča pripravo potencialnih izdelkov z visoko dodano vrednostjo – ksantofilnih estrov s povečano kemijsko stabilnostjo.

Keywords

japonski dresnik;Fallopia japonica Houtt;ksantofili;estrenje;ksantofilni estri;stabilnostne študije;kromatografije;HPLC;HPTLC;GC;masna spektrometrija;doktorske disertacije;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UL FKKT - Faculty of Chemistry and Chemical Technology
Publisher: [V. Metličar]
UDC: 547.979.8:543.544:543.51(043.3)
COBISS: 103075843 Link will open in a new window
Views: 311
Downloads: 24
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Other data

Secondary language: English
Secondary title: Stabilization of carotenoids isolated from invasive alien plant species and characterization of their preparations
Secondary abstract: Carotenoids in mature (green) and senescing leaves of invasive alien plant species Japanese (Fallopia japonica Houtt) and Bohemian (Fallopia x bohemica) knotweed were identified and quantified. Both plants showed similar pigment profiles.The amount of free xanthophylls and carotenes was significantly lower in senescing leaves in comparison to green leaves. On the other hand new xanthophyll compounds appeared in senescing leaves – xanthophyll fatty acid esters. Particularly green leaves of both studied knotweeds represent a rich and sustainable natural source of bioactive carotenoids, mainly β-carotene (69–97 mg/100g D.W.) and xanthophyll lutein (97–144 mg/100g D.W.), thus exploitation of these invaders can be used for the production of high added-value products. However, due to carotenoids chemical structure, they are very unstable outside of the plant matrix and they degrade fast in the presence of elevated temperature, light, oxidants, acids and metals. We found an inspiration to solve this problem in nature itself, where in autumn xanthophylls are converted into more chemically stable xanthophyll esters. To this end, we developed the first environmentally friendly and economically viable synthetic platform, where overall green, renewable, GRAS and recyclable materials were used. The synthesis was carried out in β-pinene as the reaction solvent and at ambient conditions (room temperaure, Atmospheric pressure), where 55 different xanthophyll esters (combining 5 model xanthophylls with 11 structurally and electronically distinct acid anhydrides) were prepared. We have shown that esterification can be performed also without use of a solvent and by exploitation of a waste plant material, e.g. extract of green leaves of Japanese knotweed or avocado peels, which represent rich renewable source of lutein and anteraxanthin, respectively. The synthesized compounds were purified and characterized by means of HPLC-PDA-MS and offline HRMS. Out of 55 compounds, 22 were successfully synthesized for the first time. The efficiency of our approach to achieve higher chemical stability of xanthophylls via esterification was tested on 13 different lutein diesters, which were synthesized either from pure lutein or from green leaves extract of Japanese knotweed. Each individual lutein diester was separately examined at each individual stress conditions: elevated temperature (60 °C), light (UV-A), oxidant (H2O2) and acidic environment. Based on systematic stability studies, we were first to identify a relationship between the chemical stability, chemical structure and the environment by which lutein esters were surrounded. Of all the prepared lutein esters, lutein di(2,2-dimethylpropanoate), lutein di(2-methylpropanoate) and lutein di(3- methylbutanoate) proved to be the most stable. They showed to be 1,4–20 times more stable than free lutein, regardless of the chosen stress condition. Depending on the stress condition the plant matrix can strongly (positively or negatively) affect the stability of an individual xanthophyll. The green leaves of Japanese knotweed, therefore, represent a suitable plant waste material that enables the preparation of potential high value-added products – xanthophyll esters with increased chemical stability.
Secondary keywords: Japanese knotweed;carotenoids;xanthophylls;esterification;xantophyll esters;stability;chromatography;mass spectrometry;Karotenoidi;Disertacije;Univerzitetna in visokošolska dela;
Type (COBISS): Doctoral dissertation
Study programme: 1000381
Thesis comment: Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo
Pages: XV f., 120 str.
ID: 14900676