Cascade strategies for the full valorisation of Garganega white grape pomace towards bioactive extracts and bio-based materials

Agro-waste reduction and reuse are among the current main social challenges. In this perspective, the present research was aimed at the complete valorisation of Garganega grape pomace by recovering bioactive phenol extracts and by testing the solid fibre extract residues in composite formulation for packaging applications. The pomace was derived from white wine production, therefore, respect to red pomace, it was promptly removed from must after pressing, and its exploitation can be particularly interesting and valuable as still rich in active compounds. Phenol extracts were obtained both via solvent-based and pressurised liquid extractions and their phytochemical compositions were compared in terms of total amount of phenols, flavonoids, flavanols, anthocyanins, hydroxycinnamic acids, and reducing sugars. Antioxidant activity and detailed phenol profiles were also achieved. The highest phenol yield was obtained via solvent-based extraction with 75% acetone (v/v), solid/liquid ratio 1:5, 2h incubation at 50°C (77.9 gGAeq/kgDW). The fibrous solid residue of the extraction was characterized via thermogravimetric analysis and used for composite preparation by melt mixing with the renewable and biodegradable PHBV polymer through a green approach (solvent-less process). The composites resulted thermally stable at high temperatures, showing initial degradation processes only at temperatures higher than 250°C. Differential scanning calorimetry analyses were carried out to study melting and crystallization phenomena, while mechanical properties were investigated by tensile tests. The materials finally showed properties similar to those of the matrix. The bio-composites can be considered as an alternative to plain PHBV, since they are less expensive and ecofriendlier thanks to a reduced polymeric content, and they could represent a suitable way for full agro-waste exploitation.