## 4 Conclusions  
In this work, the development of green circular protocol for the valorization of grape stalks has been carried out by applying process intensification technologies. Firstly, US  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **Biomass** & **LevA** & **LevA** & **Conversion (\%) a** \\  & & **Molar Yield (\%)** & **Ponderal Yield (\%)** & **Conversion (\%) a** \\ \hline
1 & This work & ChLevA Delignified GS & 85.1 & 60.9 & 68.5 \\
2 & This work & Untreated GS & 68.6 & 49.1 & 79.0 \\
3 & Reference [25] & PHTP b & n.d. c & 63.0 & 78.0 \\ \hline \end{tabular}  
*. Related to ponderal yields. b. PHTP: post-harvest tomato plant. c. non-determined.  
\end{table}
Table 3: Conversion of grape stalks (GS) to levulinic acid (LevA). Reaction conditions (considering previous work [25]): 225 \({}^{\circ}\)C, 2 min, 40 bar N\({}_{2}\). MW-assisted radiation (2.45 GHz, 1500 W).  
assisted delignification with NaDESs was performed. ChLevA afforded yields higher than 70% in a 60 min treatment, in contrast to alkaline conditions and the others ChCl-based NaDES. This step also led to the recovery of the pertinent lignin framework, as well as the liquid fractions rich in antioxidants, thus enabling the consideration of exploiting GS as a source of biologically active compounds (BACs). In this context, the obtained crude fraction from the delignification with ChLAGly (120 min treatment) showed the best scavenging power. Finally, the remaining cellulose-rich fraction was converted under MW to obtain LevA, with molar yields around 85% in a 100% selective transformation. This LevA could be used to regenerate ChLevA, which can efficiently delignify GS in a circular protocol towards the full biomass valorization. This work paves the way to a bio-refinery based on winemaking wastes by means of green protocols with enabling technologies, which supposes a valuable achievement in terms of sustainability due to the large number of by-products generated during the winemaking process. The present novel cascade protocol is well-suited for the full valorization of agricultural lignocellulosic waste.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12157417/s1](https://www.mdpi.com/article/10.3390/app12157417/s1)]([https://www.mdpi.com/article/10.3390/app12157417/s1](https://www.mdpi.com/article/10.3390/app12157417/s1)), Table S1: Fiber analysis for grape stalks (GS) according to the National Renewable Energy Laboratory (NREL) procedure. Figure S1: GC-MS analyses of the liquid fraction obtained after lignin isolation from GS delignification via UAE (40 kHz, 200 W): alkaline delignification (a), ChLAGly (b) and ChLevA (c) at 120 min treatment. Figure S2: HPLC chromatograms of the liquid fraction obtained after lignin isolation from GS delignification via UAE (40 kHz, 200 W): ChLAGly (a) and ChLevA (b) at 120 min treatment; Figure S3: GC-MS (a) and NMR (CDCl\({}_{3}\), 600 MHz) (b) analyses for the transformation to levulinic acid (LevA) from GS. Reaction conditions detailed in Table 3. References [50, 51, 52] are cited in the supplementary materials.  
Conceptualization, S.T. and M.S.-R.; Methodology, M.S.-R. and F.M.; Formal analysis, F.M. and M.S.-R.; Investigation, E.C.G.; Resources, A.M. and G.C.; Data curation, M.S.-R.; Writing--original draft preparation, M.S.-R. and E.C.G.; Writing--review and editing, S.T. and G.C.; Supervision, S.T. and A.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The data presented in this study are available in Supplementary Materials.  
This work was supported by the University of Turin (Ricerca locale 2021).  
The authors declare no conflict of interest.