Biorefinery concept for the valorization of grapevine shoots: Study case for the Austrian variety Grüner Veltliner

Abstract

Identifying feedstocks and their integral valorization is essential for the sustainable production of chemicals, materials, fuels, and energy. Waste materials from different agricultural activities can be a potential source. Specifically, winemaking and grape crops are a source of both the large amounts and variety of residues. The grapevine shoots are the primary residue resulting from the pruning of grape crops, consisting of the stems and leaves. More than 46 thousand hectares in Austria are dedicated to grape crops, and almost half of this area corresponds to the variety Grüner Veltliner. Italian, Portuguese, and Spanish grapevine residues have been studied to produce bioactive compounds; however, the most important Austrian grape variety has not been thoroughly studied for this purpose. The grapevine shoots offer different lignocellulosic platforms and valorization strategies if the leaves and stem are evaluated separately. This work evaluated the extraction of bioactive compounds and the production of hemicellulosic sugars, lignin, and a cellulose-enriched pulp from Grüner Veltliner's grapevine shoots under a biorefinery concept. Pressurized Liquid Extraction was the selected technology for extracting bioactive compounds, and Liquid Hot Water and Organosolv were chosen for hemicellulose and lignin hydrolysis. Quercetin was the flavonoid found in higher concentrations in the leaves (10.6 mg/g of dry feedstock) and resveratrol in the stems (1.9 mg/g of dry feedstock); both components were found in higher yields than other grape varieties reported in the literature. In addition, hemicellulose and lignin hydrolysis reached yields (0.18 and 0.08 g/g of dry feedstock, respectively) in the same order of magnitude as other feedstock used for hemicellulose and lignin valorization (e.g., wheat straw). These results clearly show the potential of this under-valorized feedstock and encourage further study of the downstreaming of the intermediate products and a deeper study of the production cycle of the shoots to determine the actual available amount to be used.