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1.
Simultaneous GC-MS determination of free and bound phenolic acids in Slovenian red wines and chemometric characterization
Milena Ivanović, Maša Islamčević Razboršek, Mitja Kolar, 2016, original scientific article

Abstract: Several phenolic acids (PAs), caffeic, vanillic, syringic, p-coumaric and ferulic acid, found in Slovenian red wines were studied using gas chromatography and mass spectrometry (GC-MS). For isolation of the PAs from wine samples, solid phase extraction (SPE) using hydrophilic modified styrene - HLB cartridges was used. The bound PAs were extracted after basic hydrolysis and o-coumaric acid was used as the internal standard (ISTD). The method developed was validated and the linear concentration range for all analytes was from 1 to 100 mg L$^{-1}$ with correlation coefficients above 0.999. We show that the method is repeatable (RSD<2%), recoveries were above 96%, and LOD and LOQ values were acceptable. In all of the wine samples tested, caffeic and p-coumaric acid were determined to be the predominant PAs (17-72 mg L$^{-1}$), while other compounds were found in lower concentrations. Principal Component Analysis (PCA) and Cluster Analysis (CLU) were used to study differences between wines related towards varieties and Slovenian wine regions. The results demonstrate that variety has more influence on PAs content than wine regions in Slovenian red wines.
Keywords: phenolic acids, Slovenian red wines, gas chromatography, mass spectrometry, PCA, CLU
Published: 25.08.2017; Views: 533; Downloads: 194
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2.
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: 11.04.2018; Views: 659; Downloads: 65
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