Chemical and sensory characterization of DOCG wines from Marche region (Italy).

The present thesis work has been divided into two main chapters. The objective of the first and principal project was to perform the chemical and sensorial characterization of the five DOCG wines produced in Marche region, with the aim to valorise a product of excellence that is worldwide exported and appreciated. The chemical characterization has been performed by taking into account the fundamental classes of compounds able to contribute to the organoleptic characteristics of wines, being volatile and phenolic substances, minerals and organic acids. This has been carried out to try to identify those molecules which could be used as markers to assess Marche region DOCG wines authenticity. The sensorial analysis of wine samples has been performed with the aim to describe their organoleptic features and to find the possible correlation with the chemical fingerprint discriminating one DOCG over the other and thus, further valorising a product of excellence of Marche region. This was carried out by taking into consideration also the DOCGs subgroups. Indeed, for “Offida” DOCG, “Pecorino”, “Passerina” and “Rosso” have been considered and, in the same way, for “Vernaccia di Serrapetrona” DOCG the two typologies “sweet” and “dry” were included. Furthermore, in order to obtain a sampling that was more representative of the wine market in the region, 18 wine samples (2-3 for every DOCG) were collected considering the wineries with higher sales. The analysis of the volatile substances was performed due to their importance in defining wine aroma. This was carried out by using a new developed solid-phase microextraction method coupled to gas chromatography-mass spectrometry (SPME-GC-MS) analysis. Extraction by SPME includes two steps: a direct immersion followed by head space with the use of an overcoated-fiber. By the analysis of the 18 wine samples, it was possible to detect and identify 50 volatile compounds and, in order to better investigate the results, they were divided into six different groups, according to the chemical class (ethyl esters, other esters, alcohols, acids, terpenes and others). The predominant classes of compounds were ethyl esters, followed by alcohols, even if the composition was quite variable among DOCGs. Moreover, the analyses underlined the presence of compounds which were associated to characteristics scents of the samples investigated, or which could be possibly used as authenticity markers for DOCG wines investigated. For example, the high presence of ethyl esters in “Verdicchio di Matelica” was able to explain the yellow pulp fruity aroma perceived by the panel during the sensorial analysis. The analysis of short and medium chain free fatty acids was performed by using a new developed and validated liquid-liquid extraction procedure followed by gas chromatography coupled to flame ionization detection (LLE-GC-FID) analysis. This class of compounds is of huge importance when considering the wine quality and the method permitted the quantification of acetic, propionic, isobutyric, isovaleric, hexanoic and octanoic acids. The main differences raised between the composition of white and red wines, the first being more enriched in hexanoic and octanoic acid, while the latter in acetic, propionic, isobutyric and isovaleric acids. For every analyte, the AOV (active olfactory value) was also calculated to assess the compounds that may play an active role in the aroma of the samples investigated. Interestingly, for every analyte (with except for propionic acid) AOV values >1 were obtained, meaning that these analytes may actually take part to the overall aroma of DOCG wines. Concerning the phenolic profile, it was assessed by performing high performance liquid chromatography coupled to tandem mass-spectrometry (HPLC-MS/MS) analyses and a total of 37 compounds were detected and quantified. As expected, red wines were much more enriched in polyphenols when compared to white DOCG wines. The different statistical approaches evidenced the presence of some peculiarities able to discriminate wines made with same grape variety, or wines produced in close geographical areas. As an example, “Offida Rosso” and “Cònero” which are produced with a minimal amount of 85 % of Montepulciano grape variety showed a similar polyphenolic profile. At the same time, “Offida Rosso” showed the highest concentration of vanillic acid, which makes this compound a possible authenticity marker of this wine typology. When considering minerals, among the 40 elements quantified by inductively coupled plasma-mass spectrometry (ICP-MS) analysis, five were selected, being considered the ones not consistently altered by oenological practises (and thus, more linked to the soil composition of origin). These elements were Sr, B, Ba, Li and Mn, but, when performing different statistical approaches, a clear discrimination did not raise between wines produced in different part of the region, which can be due to the relatively small production geographical area. Regarding organic acids, six compounds were identified by HPLC coupled with diode array detector (HPLC-DAD) analysis with an analytical method which is currently under optimization. In particular, tartaric, isocitric, shikimic, lactic, succinic, citric and malic acids were identified and quantified. The statistical analyses of samples underlined a difference in the concentrations of acids when comparing white and red DOCGs. White wines were generally enriched in tartaric and isocitric acid, with the first being the main responsible of wine acid taste. As expected, red wines showed higher concentrations of lactic and malic acids, but also of succinic acid. Shikimic acid, which is considered to be able to discriminate grape varieties, showed characteristic concentrations. At the same time, every DOCG was characterized by a peculiar organic acid profile, which should be better investigated to confirm its usefulness to assess their authenticity. Finally, through the sensorial analysis it was possible to point out features able to characterize the 5 DOCGs with distinctive organoleptic profiles. Indeed, for example, “Verdicchio di Matelica Riserva” and “Castelli di Jesi Verdicchio” were described by the typical anise aroma and were the samples more enriched in methyl salycilate, which is a compound able to give the particular note. Also, some differences raised between the two “Offida” white wines (“Pecorino” and “Passerina”), which were described by different scents. Also differences between red wines raised, being the “Cònero” and “Offida Rosso” described by diverse aspect and scents. Finally, “Vernaccia di Serrapetrona” wines were the ones more described by tertiary aromas, such as cinnamon scents. In this project, both the chemical fingerprint and the sensorial analysis were able to underline substantial differences between the five DOCG wines produced in the region and, by further confirmations, their chemical fingerprints could be used in the future to assess their authenticity. In order to do that, further developments should be performed, by considering both more wineries and different vintages. Also, the sensorial analysis should be performed by following quantitative methods. Indeed, by selecting a panel of judges and by training the panel to describe the sensory characteristics of the DOCG wines investigated, a more reliable correlation could be performed able to fully characterize the sensorial and chemical profile of these wines of excellence. The second part of the thesis regards the project that was carried out during the period January-June 2022, in the Laboratorio de Análisis Aroma y Enología (LAAE) at the University of Saragozza (Spain). The study was focused on the optimization of a solid-phase extraction (SPE) procedure in order to concentrate and isolate five polyfunctional mercaptans from wine. These compounds are known to play essential roles in the organoleptic characteristics of wines. In particular, in this study, the five mercaptans considered were 4-mercapton-4-methyl-2-pentanone, furfurylthiol, benzyl mercaptan, 3-mercaptohexanol and 3-mercapto hexyl acetate, which are known to be amongst the most abundant in wine. The SPE procedure has been optimized by taking into consideration all the steps involved (loading of the sample, cleaning, washing and final elution) and by also exploiting the CuCl salt to form strong Cu(I)-S complexes that were found to be essential for the retention of mercaptans in the sorbent phase. Finally, an SPE procedure was optimized which enabled to obtain very pure extract. The conditions for the final extract analysis are still under optimization through stir bar sorptive extraction (SBSE) coupled to a thermal desorption system (TC-GC-GC-MS) aimed to lower the sensitivity of the method and to proceed with the subsequent validation.