Supervisors info:
Ανδρεάνα Ν. Ασημοπούλου, Αναπληρώτρια Καθηγήτρια στην Εφαρμοσμένη Οργανική Χημεία - Φυσικά Προϊόντα, Εργαστήριο Οργανικής Χημείας, Τμήμα Χημικών Μηχανικών Α.Π.Θ.
Summary:
Wine is one of the most popular beverages in the world. Different analytical techniques have been developed for the determination of several constituents in wine samples and grapes. Regulatory agencies are demanding improved methods to ensure compliance with labelling, safety requirements and wine authenticity. In that frame, robust analytical methods have been developed in recent years to enable wines’ authenticity, but also to improve the winemaking process and technology. The application of modern analytical spectroscopic techniques on the determination of constituents of grapes, must and wine, continue to present tremendous challenges. In this study, the profiling of grapes and must constituents was performed. In particular, grapes from Muscat of Alexandria variety, as well as grape must sampled at different days of alcoholic fermentation were analysed by an untargeted LC-HRMS profiling method and Raman spectroscopy. The aim of this work was to obtain a comprehensive profile of the metabolites present in the samples, to identify them and monitor their differentiation among vineyards, grape ripening periods and throughout the alcoholic fermentation period.
Grapes were collected from three vineyards from Lemnos island, Greece, while the grape must samples were kindly donated by the winery of the Agriculture Cooperative of Lemnos. An UHPLC method, utilizing an UPLC C18 column, in hyphenation with Ion Trap-Orbitrap hybrid mass spectrometer in positive ESI mode was performed. Several secondary metabolites were identified (phenols, stilbenes, amino acids) and their peak area was monitored in all samples. Multivariate analysis was performed to reveal trends in the samples in relation to sampling location or ripeness.
Furthermore, Raman spectroscopy was utilized to investigate its potential in wine analysis. The near infrared laser line at 785 nm, from the available wavelengths at 515, 633 and 785 nm, was best suited for excitation of the Raman spectra in our case. The resulting signals indicated specific fingerprints of sugars (fructose and glucose in particular), ethanol and water. Using standard compounds, the conversion of sugars to ethanol was monitored and a semi-quantification of these compounds was performed.
An analysis was, also, carried out by ultraviolet visible (UV-VIS) spectroscopy to obtain a full spectroscopic view of the samples.
Lastly, the sediments which emerged after the centrifugation of the grape must samples were analyzed by ultraviolet spectroscopy (ATR-FT-IR) to investigate their components.
Keywords:
wine, profiling, UHPLC-HRMS, Raman spectroscopy
