Circular economy and integrated supply chains for exploitation of the waste biomass coffee silverskin to valuable antioxidant polyphenols

Coffee is one of the largest consumed drinks all over the world generating, every year, a very significant amount of wastes during the beans processing. Among these by-products, coffee silverskin is a very interesting waste product deriving from the roasting process. Today, it has been estimated that 0.8 tons of coffee silverskin are produced on 100 tons of final coffee. Up to now, these waste residues have no specific use, being mostly discharged in landfill or burned. On the other hand, in recent years, coffee silverskin has attracted great attention as promising source of bioactive compounds, including polyphenols and caffeine. However, in order to valorize these valuable components, they should be isolated from the starting matrix through suitable processes and, in this regard, recently, several extraction methods with different complexity, cost and yield have been applied. Among them, microwave-assisted extraction results particularly efficient, nowadays garnered increasing interest in various fields. On this basis, the aim of the present research is the investigation and the optimization of the solid-liquid extraction of valuable antioxidant polyphenols from coffee silverskin, under microwave irradiation. The influence of the main reaction parameters, such as temperature, extraction time and composition of the solvent, consisting of a binary mixture of water/ethanol, has been assessed, also employing statistical modeling. The achieved polyphenols yields are higher than those reported in the literature, thus leading to an important step forward, in the perspective of improving this waste recycling in a circular economy perspective.