Biorefinery strategy for winery waste: a multi-step process based on “green” pressurized fluids

Winemaking generates a significant amount of waste. Grape marc, the main solid residue, constitutes 20-25% of the pressed grapes and approximately 8-9 million tons are produced globally each year1. The huge amounts, combined with the seasonal nature of the winemaking process, pose significant disposal, management, and environmental challenges. In this context, the biorefinery concept for the sequential utilization of a biomass to obtain multiple products gained great interest. Generally, different chemical, physical and biological techniques are exploited and combined to maximize the biomass valorisation and economic profits. However, the integration and maintenance of multiple types of equipment make the economic feasibility of this approach challenging2. A more feasible and effective approach could be the exploitation of a single versatile technology. A novel biorefinery strategy to sequentially extract multiple compounds using green pressurized fluids was investigated. The multi-step extraction process involved three sequential phases: a) lipids extraction using supercritical CO2 (SC-CO2); b) polyphenols extraction using a hydroalcoholic mixture at subcritical state; c) polysaccharides extraction using subcritical water (SCW). The solid residue from each step were used as the raw material for the subsequent step. All the extracts were quantified, chemically characterized, and compared with conventional ones. The SC-CO2 achieved extraction yields comparable with conventional solvent extraction, with the advantages of ensuring a faster and free-solvent process3. The 50% ethanol-water mixture at subcritical state increased 1.5-fold the polyphenols content, and the kinetic curves pointed out a 4-fold decrease in extraction time4. Furthermore, the SCW led to a 4-fold increase of polysaccharides content compared to conventional extraction, with a remarkable 30-fold decrease in process time. Appropriate scalability studies, based on mathematical modelling, and techno-economic evaluations are now necessary to effectively assess the potential transferability of this biorefinery strategy to an industrial scale.