3.1.2. Stilbene Composition

The stilbene concentration (Rsv and Vf) as affected by each treatment is shown in Table 3. First of all, we determined that the variety influenced the stilbene content. In fact, untreated Negramaro vine shoot extracts contained a higher concentration of Rsv compared to Primitivo (5249.4 vs. 1861.3 mg kg−<sup>1</sup> DW), while the latter had a higher concentration of Vf (1531.6 vs. 600.1 mg kg−<sup>1</sup> DW).

It was evident that the drying treatment accounted for some variations in the Rsv and Vf concentrations, according to what we observed for TPC (Table 2). With respect to the Primitivo vine shoots, the drying at 50 ◦C for 24 h determined the reduction of Rsv (1663.8 ± 16.3 mg kg−<sup>1</sup> DW) and Vf (1356.8 ± 10.0 mg kg−<sup>1</sup> DW) when compared to the untreated vine shoots (1861.3 ± 9.8 mg kg−<sup>1</sup> DW for Rf and 1531.6 ± 89.1 mg kg−<sup>1</sup> DW for Vf). Minor differences were observed when comparing the other two treatments with the untreated sample: the Rsv concentration increased by only 6.6% after the treatment at 70 ◦C for 15 min and decreased slightly after the treatment at 80 ◦C for 10 min (1763.4 ± 98.3 mg kg−<sup>1</sup> DW); after the treatment at 70 ◦C for 15 min and 80 ◦C for 10 min,

the concentration of Vf increased by 13% and 5.6%, respectively. Thus, no significant differences were found between the concentrations of Vf after these two treatments. In regards to Negroamaro, significant differences were found among the treatments, with the untreated sample showing the highest Rsv (5249.4 ± 129.8 mg kg−<sup>1</sup> DW) and Vf concentrations (600.1 ± 79.0 mg kg−<sup>1</sup> DW) (Table 3).

**Table 3.** The stilbene concentrations in Primitivo and Negramaro vine shoot extracts. The means and standard deviation (*n* = 2) are represented in the same column and different letters for each variety indicate significant differences (*p* < 0.05).


Overall, these results sugges<sup>t</sup> that the heat pre-treatments either left unchanged or caused a decrease in the stilbene concentration. In particular, the treatments with lower temperatures and longer times led to a significant reduction in Rsv and Vf. Most likely, the use of high temperatures may promote the degradation of some compounds, as reported by Piñeiro et al. [39]. In that case, in most of the selected vine shoots (from 15 grape cane varieties), the total stilbene concentration was significantly higher for freeze-dried extracts than for oven-dried extracts (40 ◦C for 15 days). However, our results are in contrast with those from Sánchez-Gómez et al. [40], who showed that the thermal treatment led to Rsv concentrations from 6 to 14 times higher than those in the control/no heat treated samples, depending on the vine variety (Airén and Moscatel grape canes).

To the best of our knowledge, this is the first report on the effect of these timetemperature drying parameters on the vine shoot stilbenes contents of Italian vine varieties.

### *3.2. Evaluation of Different Italian Varieties*

Considering the results previously obtained, no heat treatment was applied to characterize the stilbene contents in the vine shoots of the investigated Italian varieties. Indeed, in absence of clear advantages, the heat-treatment results are a waste of energy, incompatible with the requests for sustainable processes.

### 3.2.1. Total Phenolic Content and Antioxidant Activity

The total phenolic contents of the vine shoots are given in Table 4. Vine shoots from the Sangiovese variety showed the lowest TPC, which was approximately 60% lower than Palieri, the variety with the highest content. These results agree with previous studies [50,51]. In fact, Çetin et al. [51], in evaluating the chemical composition of ten different Turkish grape canes varieties, showed that the total phenolic content changed significantly according to the varieties (in a range from 25.36 ± 1.62 to 36.56 ± 2.67 mg GAE g<sup>−</sup><sup>1</sup> DW). Similarly, according to Dorosh et al. [50], the amount of total phenolic content in Tinta Roriz vine shoot extracts (32.6 ± 2.1 mg GAE g<sup>−</sup><sup>1</sup> DW) was 1.6 fold higher than the value obtained from the Touriga Nacional variety (20.1 ± 0.6 mg GAE g<sup>−</sup><sup>1</sup> DW), for the same extraction time and ultrasound extraction technique. These results were in agreemen<sup>t</sup> with those from a previous study that also presented a summary table showing the results from selected published papers examining the phenolic compounds of vine shoots extractions [48].


**Table 4.** The total phenolic content and antioxidant activity of vine shoot extracts from 23 different Italian varieties. Means and standard deviation (*n* = 2) are represented in the same column and data followed by different letters indicate statistically significant differences according to the Fisher test (*p* < 0.05). For sample codes, see Table 1.

Table 4 shows the antioxidant properties of the extracts from the vine shoots of the Italian varieties evaluated. The antioxidant activity showed statistically significant differences among the varieties with the same tendency as that previously described for TPC. As reported in Table 5 and as previously demonstrated, antioxidant activity correlates with the total phenolic content of grape cane extracts [52]. These results were quite consistent with those provided by the DPPH assay, since the Palieri, Montepulciano, and Notardomenico vine shoot extracts showed the highest antioxidant capacity (112.1 ± 0.6, 111.6 ± 0.8, and 115.2 ± 1.2 μmol TE g<sup>−</sup><sup>1</sup> DW, respectively) and, at the same time, the highest total phenolic content. Additionally, according to the ABTS assay, the Montepulciano vine shoot extracts had the highest antioxidant activity (156.4 ± 0.8 μmol TE g<sup>−</sup><sup>1</sup> DW). It is very difficult to compare the results obtained from this characterisation with those from other studies because most of those used different assays to evaluate the antioxidant activity. Nevertheless, some researchers have compared the antioxidant activity of vine shoot extracts of different varieties [45,49,50]. For example, Guerrero et al. [18] found significant differences in the antioxidant activity of the vine shoots from 22 grape varieties (including *Vitis vinifera sativa*, *Vitis vinifera sylvestris,* and hybrid direct producers), measured using the oxygen radical absorbance capacity (ORAC) assay (range from 1700 to 5300 μmol, Trolox equivalent g<sup>−</sup><sup>1</sup> DW).
