Green next generation biomaterials from virtuous recovery of grape processing waste bentonite

The waste valorisation, by conversion of discharge products into novel high value-added biomaterials, represents a virtuous strategy to contribute to the ecological transition while producing social, economic and scientific repercussions. Even more, the recycle of wastes from the local resources could maximize the impact of the circular economy idea by enhancing the territorial resources and creating new products free from additional raw materials consumption. About this, the grape processing industry is an undoubted Sicilian prestige, but it also produces abundant both organic and inorganic wastes. While grape pomace has been extensively valorised in the last years, the inorganic wastes have never been considered yet. The latter are mainly the fining agents, among which bentonite is the most common one. It is a mineral clay widely used due to low cost, abundance in nature, high clarifying power and ease of separation from the fined product by sedimentation. So far, the bentonite is just an abundant waste (100g of bentonite to fine 1hL of must/wine) then the aim of this work is to recognize it as a precious source of polyphenols to be given new life by extraction. The frozen waste black bentonite was supplied by Bono&Ditta S.p.A. Once arrived at the University of Palermo it was subjected to pulverization, sieved, divided into aliquots identified as belonging to the same lot and stored at -80°C. Samples of bentonite were subjected to green extraction by maceration (1h, 25°C, constant stirring, in the dark) choosing unconventional extraction solvents among well-known and currently used hydrophilic liquid excipients for pharmaceuticals and cosmetics. They were PEGs (PEG200, PEG400, PEG600), propylene glycol and glycerine, selected due to their high solvent power toward polyphenols and biocompatibility. The coloured liquid extracts were characterized and compared in terms of antioxidant power/scavenging activity by DPPH assay, chromatographic profile and extracted amount of some representative polyphenols by HPLC-DAD analyses, total phenolic and protein contents by Folin-Ciocalteu and Bradford assays respectively. The best extract was obtained by using PEG200 and was then further studied. It resulted stable at easily achievable storage conditions (4°C, in the dark) for at least 6 months. Furthermore, it is suitable as a novel, value-added biomaterial for biomedical and cosmetic purposes as nor skin/eye irritation neither skin sensitising potential emerged by the in vitro tests, according to OECD 439/492/442E guidelines. Importantly, the “green soul” of this work is not just related to waste bentonite valorisation. The extraction procedure can be considered eco-friendly both in terms of employed technique and chosen extraction solvents. This choice perfectly fit with an industrial, easily scalable and waste-to-market approach as well as with the SDGs 12, 8 and 3 of the UN agenda 2030.