**1. Introduction**

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> Stilbenoids are a natural family of polyphenolic compounds that exist both as monomers and as oligomers, with a diphenyl ethylene group oriented in cis or trans configurations [1]. These compounds have gained interest not only for their several biological activities, but also for their complex structural conformation [2]. Numerous studies show that the beneficial properties of stilbenes for human health include protective effects against cancer (as they inhibit cell proliferation) [3], diabetes [4], neurodegenerative diseases such as Alzheimer's disease [5], and coronary heart disease [6]. They are also used as multifunctional ingredients in cosmetics [7]. Recently, the possibility of developing drugs against COVID-19 using natural stilbene compounds has been evaluated [8]. In addition, stilbenes are used in agriculture as alternative anti-phytopathogenic substances [9,10].

> Stilbenes are mainly synthesized by plants as phytoalexins in response to biotic and abiotic stress (e.g., pathogens, ultraviolet irradiation, heavy metal ions, mechanical damage, frost, thermal treatment, or ozone) [11]. Their distribution is very heterogeneous in the plant kingdom [12]. In fact, stilbenes have been isolated and identified in at least 72 plant species belonging to 31 genera and 12 families, including *Vitaceae,* in which these compounds are present in lignified stem tissue, in grape berries and in wines [11,13,14]. Several reviews have indicated that winery wastes and by-products are rich in stilbenes, which have been extracted and applied in multiple fields based on their beneficial properties [15,16].

**Citation:** Noviello, M.; Caputi, A.F.; Squeo, G.; Paradiso, V.M.; Gambacorta, G.; Caponio, F. Vine Shoots as a Source of *Trans*-Resveratrol and *ε*-Viniferin: A Study of 23 Italian Varieties. *Foods* **2022**, *11*, 553. https://doi.org/10.3390/foods11040553

Academic Editor: Maria Cecilia do Nascimento Nunes

Received: 16 December 2021 Accepted: 14 February 2022 Published: 15 February 2022

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The cultivation of vines is widespread: in 2020, the world area under vine cultivation for all purposes (wine and juices, table grapes, and raisins) was estimated at 7.3 million hectares (Mha), of which 3.3 Mha are in the European Union. Italy has an area under vine cultivation of 719 thousand hectares, an increase of over 0.8% from 2019 [17]. Consequently, the wine-growing sector produces many and various wastes, generated from agricultural practices (e.g., vine shoots, leaves, stems) as well as from the winemaking process (e.g., grape stalks, pomace, wine lees). In particular, vine shoots (also called grapevine canes) are the most significant vine waste material from a quantitative point of view, with a weight of 2–5 tonnes per hectare per year, depending on density of plantation, climate, vigour of the vine, and other agronomical factors [18].

Vine shoots have a very low economic value; in fact, they are burned [19] or incorporated into the soil to promote the degradation of organic matter and reduce the need for organic fertilizers [20]. Some other possible applications of this material include the production of pulp paper [21], solid biofuels [22], or the possibility of obtaining activated carbon [23]. Recently, attention has shifted to the possibility of using vine shoots in the agrifood industry, in a circular economy perspective. One of the possible applications studied is their use as an alternative to oak chips as an enological coadjuvant to improve the sensorial profile of wines, [24,25]. Moreover, recent studies have shown that vine shoots are rich in bioactive compounds, such as stilbenes, that make this by-product an untapped source of these compounds with important antioxidant, anti-microbial, and anti-aging properties and multiple possible applications [15]. Up to 41 stilbenes have been found in vine shoots and among these, *trans*-resveratrol (Rsv) and *ε*-viniferin (Vf) are the most abundant [15,26]. Several studies tested stilbene-enriched vine shoot extracts as a preservative in wine in order to reduce the use of SO2 in winemaking [15,27].

The concentration and composition of stilbenes in vine shoots are subject to extreme variability due to many intrinsic and extrinsic factors. These factors include the variety and geographical area of origin [28–30], vineyard age [31], or climate conditions [32]. Considering the variety analysed in literature, vine shoots of Pinot Noir and Gewurztraminer have been reported as those with the highest content of stilbenes [15,18,29,30]. On the other hand, the extrinsic factors include the extraction method [26], storage time and temperature of the vine shoots, or various pre-treatments, such as the cutting length or thermal treatments, before stilbenes extraction [32–38]. Despite the available reports, the literature does not clarify univocally the effects of these heat treatments on stilbene quantities [26,39,40]. Moreover, it is well known that the low-temperature/long-time heat treatments, mostly adopted for vine shoots, generally led to a higher reduction of the nutritional values of foods than the high-temperature/short-time heat treatments [41]. A previous work proved that treatments applied to Coratina olive cultivar leaves at high temperatures and short times did not cause a reduction of the phenolic compounds [42]. Consequently, investigations on the effect of the temperature-time conditions are necessary to preserve these compounds and increase the extraction yields.

The aim of this study was twofold: (i) select the most appropriate vine shoots treatment before stilbene extraction (untreated, dried at 50 ◦C for 24 h, dried at 70 ◦C for 15 min, dried at 80 ◦C for 10 min) using two testing varieties (Primitivo and Negroamaro); (ii) study the variability of the total phenolic content and the Rsv and Vf amounts of vine shoots from 23 Italian varieties. To the best of our knowledge, the stilbene contents of vine shoots from these Italian varieties has not been studied yet.
