Extraction of stilbenes from grape cane waste and their possible applications

Abstract

Vine pruning residues constitute a significant fraction of vitivinicultural waste; in fact, depending on the variety and training system, they can reach 1-5 tons/ha/year. Currently, these wastes are underutilized, as they are left in the vineyard or composted. After cutting, however, if they are stored at room temperature, a strong synthesis of stilbenes is activated in the canes, in particular of resveratrol, which reaches its maximum concentration 2-3 months after harvest (reaching concentrations of up to 2.5 mg/g of dry weight). Grinding the shoots and extracting them with a hydroalcoholic solution (70% ethanol) which is then evaporated under vacuum, allows us to obtain a crude extract very rich in resveratrol. The extract also contains high quantities of Ɛ-viniferin, a dimer of resveratrol. Stilbenes belong to the class of phytoalexins, which are plant defense molecules, and in fact both resveratrol and viniferin show antifungal properties. A study performed on Vitis vinifera both in vitro and in vivo has demonstrated the possibility of using the grape cane extract, without the need for further purification, as a natural antifungal product. In particular, it has been shown that the application of the extract (titrated at 100µg/ml of resveratrol) has both a preventive and curative effect against Botrytis cinerea, but other studies have highlighted a certain potential also against Plasmopara viticola. With these premises, approximately 25 kg of shoots could provide the quantity of extract sufficient to treat one hectare of vineyard. In addition, the grape cane extract, if compared with the root extract of Polygonum cuspidatum, a plant known in traditional Chinese medicine and which is currently the main source from which resveratrol is obtained (4 mg/g dry weight), is simpler, with a reduced number of different compounds, so a possible purification step is also simpler to obtain pure molecules that could also be used in the food or cosmetic sectors. Further studies will be needed to test alternative and more sustainable extraction solvents.