High-value compounds obtained from grape canes (Vitis vinifera L.) by steam pressure alkali extraction

Abstract

The main by-product generated by the wine industry is the grape canes derived from the pruning process. The aim of the current work was the valorisation of this highly polyphenolic lignocellulosic material, by alkali extraction methodology avoiding alcoholic solvents use.In lignocellulosic by-products valorisation, it is important to take into account the variability of the raw material. In the case of vine pruning this may be due to the different varieties used, the geographical area, the climate, or the processing. It is, however, important to develop a global strategy for valorisation, from a biorefinery and circular economy point of view. In this work, the grape canes were characterised, before and after the extraction process, by Fourier transform infrared spectroscopy – attenuated total reflectance (FTIR-ATR) spectroscopy. Changes in cellulose crystallinity, hemicellulose content and structural conformation of proteins, due to the alkali thermal extraction process were identified and evaluated. For the first time, a steam pressure alkali extraction method was used on this material. The products were characterised by FTIR-ATR and Matrix Assisted Laser Desorption Ionisation-Time of Flight (MALDI-TOF) mass spectrometry. The presence of high-value compounds such as stilbene oligomers and condensed tannins was demonstrated in the extracts. The work shows the viability of the steam pressure alkali extraction, a simple and environmentally friendly method, for grape cane valorisation.