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

Coffee is one of the most consumed drinks all over the world with a production higher than 10 million tons in 2018, generating, every year, the largest amount of wastes during the coffee beans processing. Among these by-products, coffee silverskin (CS) is one of the most interesting compounds generated as a waste of the roasting process. Today, it has been estimated that for 100 tons of coffee as final product, 0.8 tons of CS are produced. Up to now, these residues have no special use, being mostly discharged in landfill or burned. On the other hand, in the last years, CS has attracted great attention as a promising source of bioactive compounds, including polyphenols and caffeine. However, in order to valorize them, they should be isolated from the starting matrix through suitable extraction processes. On this basis, the aim of the present research is the investigation and the optimization of the solid-liquid extraction from CS of polyphenols responsible for the antioxidant activityadopting microwave irradiation. The influence of the main reaction parameters, such as temperature, extraction time and composition of the solvent, 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 and this study represents a step forwardin the perspective of recycling and circular economy.