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1.
Development of analytical methods for simultaneous identification and determination of phenolic compounds
Milena Ivanović, 2018, doctoral dissertation

Abstract: The objective of this doctoral dissertation was to develop different analytical approaches for the extraction, separation, identification and quantitative determination of various phenolic compounds from different plants and their products. This dissertation is divided into the following four major segments, which, to some extent, can stand alone, but when it comes to the research, they are mutually very related: - Segment 1: Short-term (up to 24 h) and long-term (up to 1 month) stability studies of trans-caffeic acid (trans-CA) and trans-ferulic acid (trans-FA) dissolved in two organic solvents (methanol and tetrahydrofuran) and exposed to a range of storage conditions (temperature, organic solvents used, influence of daylight and UV irradiation) were performed for the first time. Gas chromatography with mass spectrometry (GC-MS) was used to study the degradation of the samples and structural identification of the degradation products. - Segment 2: The research within this segment focused on the optimization of a simple, fast and quantitative extraction method for the isolation of phenolic acids (PAs) from Slovenian red wine samples. Different extraction techniques were tested, and solid phase extraction (SPE) using HLB cartridges was selected as the optimal technique. For the identification and quantification of extracted analytes, the GC-MS method was optimized and validated. Different statistical and chemometrical tools were applied, and the wines were classified according to the Slovenian wine-growing regions and vine varieties. - Segment 3: The main goal within this research segment was the development of an ultrasound-assisted extraction (UAE) method for the isolation of different polyphenol classes from coriander fruits. Additionally, for the isolation of total PAs (free and bound), two analytical steps were applied: UAE alkaline hydrolysis and clean-up using SPE HLB cartridges. The response surface methodology (RSM) combined with a Box-Behnken experimental design (BBD) were used for the optimization of the alkaline hydrolysis and for increasing the extraction yields of the PAs. In this way, most influencing factors (temperature, sonication time and NaOH concentration) were studied as independent variables. Extracted PAs were determined using the previously optimized GC-MS method. - Segment 4: The main goal of this segment of the dissertation was to show the application of deep eutectic solvents (DESs) as a ‘green’ alternative to the conventional organic solvents for the isolation of phenolic compounds from plants such as Aronia melanocarpa (dried chokeberry) and Olea europaea (olive leaves). Different extraction techniques and instrumental methods were applied for the determination of phenolic profiles. Phenols from chokeberries were obtained through UAE. Furthermore, for the simultaneous identification and quantitative determination of 21 different phenolic compounds from Aronia melanocarpa, the HPLC-UV method was optimized and validated. On the other hand, microwave-assisted extraction (MAE) was used to improve the extraction yields of phenolic compounds from olive leave samples, which were subsequently determined by using validated HPLC-DAD-ESI-TOF-MS method.
Keywords: phenolic compounds, phenolic acids, extraction, GC-MS, HPLC, method optimization, deep eutectic solvents, plant material
Published in DKUM: 11.04.2018; Views: 2057; Downloads: 167
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2.
Phenols, proanthocyanidins, flavones and flavonols in some plant materials and their antioxidant activities
Mojca Škerget, Petra Kotnik, Majda Hadolin Kolar, Andreja Rižner Hraš, Marjana Simonič, Željko Knez, 2005, original scientific article

Abstract: Methanol extracts prepared from five plant materials native to the Mediterranean area, namely olive tree (Olea europaea) leaf, St. John's wort (Hypericum perforatum), hawthorn (Crataegus laevigata), oregano (Origanum vulgare) and laurel leaf (Lauris nobilis), were examined for their phenolic components. Total phenolic content was determined by the Folin-Ciocalteu method. The content of proanthocyanidins in acid-hydrolysed extracts was determined spectrophotometrically. The contents of free flavones (apigenin andluteolin) and flavonols (kaempferol, myricetin and quercetin) were determined by HPLC analysis. The time of hydrolysis of flavones, flavonols andproanthocyanidins was optimised. Antioxidant activities of apigenin, luteolin, kaempferol, myricetin, quercetin and of plant extracts were examined. Antioxidative activities were studied in sunflower oil at 98 °C, by measuring peroxide value, and in an aqueous emulsion system of -carotene and linoleic acid by measuring the absorbance of the sample. Among flavones and flavonols investigated, only myricetin inhibited oxidation of sunflower oil. All other flavones and flavonols showed pro-oxidative activity. Oppositely, in the emulsion system, only apigenin showed pro-oxidative activity while otherflavones and flavonols and plant extracts inhibited oxidation of -carotene.
Keywords: chemical processing, extraction, plant material, fenolic content, hidrolysis, antioxidants, flavones, flavonols, proanthocyanidines, oils, emulsions
Published in DKUM: 01.06.2012; Views: 2461; Downloads: 122
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