**1. Introduction**

Viticulture consists of the set of agronomic techniques that are used for the cultivation of the vine. From planting vines to their removal, viticulture embraces every aspect of the grape plant's life. The cultivation of vineyards is one of the most important and essential phases of the wine making process [1–3]. The first evidence of Sicilian viticulture seems to date back to the 2nd millennium BC. Influenced by the various dominations that have occurred on the island, Sicilian viticulture is today characterized by a complexity of native cultivars [4]. Sicily, with 17.5% of the national production, is the Italian region with the largest wine-growing area. In recent decades, Sicilian wines have experienced a growing expansion in the international market [5]. Indeed, since the early 1990s, Sicilian wine producers have understood the need to increase the quality of their production to compete with the market challenges of the global market [6]. Over 60% of the production is focused on quality wines with 24 PDO (Protected Designation of Origin) and 7 PGI (Protected Geographical Indication) certifications. Among the best-known and autochthonous ones are Nero D'Avola, Frappato, Nerello, Grillo, Catarratto, Carricante, and Marsala [6].

The wide organoleptic variety of these wines—from the more alcoholic and full-bodied ones to the fresher, elegant, and fragrant ones—is due not only to the grape variety, but to the different pedoclimatic conditions of the Sicilian Island [7]. The Mediterranean climate, in fact, is characterized by hilly and coastal areas with mild winters and low rainfall and hot summers, and sometimes it is sultry and ventilated, while the mountainous and inland areas are affected by a continental climate, which is cold and rigid, especially on the Etna and Madonie mountains, which strongly determines the daily and seasonal temperature variations [8]. The characteristics and production of the different cultivars are

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also influenced by the differences in the composition of the soils of the different areas [9]. For example, the lava soils of Etna are optimal for the Carricante and Nerello vines, and the calcareous and clayey soils are optimal for the Nero d'Avola vines, while those of tuff give a sugary charge and a refined aroma to the white wines, in particular to the Grillo [9].

The Grillo is a white grape variety that is famous above all for its role in the Marsala fortified wines of the island [10]. It is still widely planted in western Sicily, with there being a cultivated area of 6300 ha, despite the fall in the trend of Marsala, and it is now most commonly used in a variety of still white wines, both varietal and blended types [11]. Grillo adapts well to the hot and dry Sicilian climate and shows adequate resistance to downy mildew. Its high sugar levels and the ease with which it oxidizes make it a good option for fortification. Grillo can produce wines with an alcohol content that reaches 15/16◦ vol. [12]. In recent years, as the focus has shifted from quantity to quality, the Sicilian producers of it, thanks to the improvement of viticultural and vinicultural techniques, have begun to revisit the Grillo wines. This has produced Grillo wines of a grea<sup>t</sup> organoleptic thickness, savoury, and fragrance that are more pleasant than the rather earthy styles that were previously available. Furthermore, Grillo has the vocation of being particularly predisposed to aging for years or even decades [13].

In this regard, the present study aimed to investigate the possibility of using the total content of polyphenols as an indicator of the shelf-life of Grillo wines.

In the scientific literature, there are some studies on the subject, for example Arena et al. (2021) showed that the phenolic content in Malvasia delle Lipari wine varies over time (6 months of monitoring) and with the storage temperature (30, 35, and 45 ◦C), and that this aspect was not influenced by the colour of the glass bottle [14]. Diaz-Maroto et al. (2020) showed that after 12 months of bottle storage, a significant loss of the phenolic compounds was observed in all of the analyzed samples [15]. The same trend was found by Castellanos et al. (2021), but they also highlighted that after 12 months of storage, no changes in the phenolic content were reported [16]. Therefore, the studies on the subject do not show a univocal trend of the phenolic content during storage, so there is a bibliographic gap in the variation of these compounds in white wines during the aging period.

In this context, our research aimed to perform a polyphenolic characterization of the Grillo wines that were produced by a selected winery in the years 2011–2021 using an optimized RP-HPLC-DAD method. The data that were obtained were then processed by a chemometric analysis. In addition, the soluble solids content (SSC) and pH were determined due to their importance as quality indices in winemaking. The SSC are mainly organic sugars, such as glucose, sucrose, and fructose, which affect the taste and transparency of the wine. The pH was used as the measure of its acidity, which is due to the inclusion of organic acids such as lactic acid, malic acid, and others. Furthermore, the pH is an important parameter of complicated biochemical changes during fermentation and winemaking (e.g., degradation of some nutrients or formation of by-products) [17–21].

#### **2. Materials and Methods**

#### *2.1. Reagents and Standard Solutions*

All reagents used were analytical grade. The acetonitrile, methanol, and formic acid were provided by Merck (Darmstadt, Germany). The water was obtained from a Milli-Q water purification system (Millipore, Bedford, MA, USA). The standards of gallic acid (r2 = 0.9981), p-hydroxybenzoic acid (r2 = 0.9995), and ferulic acid (r2 = 0.9999) were from Sigma-Aldrich (St. Louis, MO, USA). The standard stock solutions of polyphenols were prepared in methanol and stored at 4 ◦C in the dark.
