Optimization study for extraction of the value-added compounds polyphenols from the waste biomass coffee silverskin in the perspective of circular economy

Coffee is one of the largest consumed drinks all over the world, generating 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. Up to now, these waste residues have no specific use. On the other hand, in recent years, coffee silverskin has attracted great attention as promising source of bioactive compounds, including valuable polyphenols as chlorogenic acids and caffeine. However, in order to valorize these valuable components, they should be isolated from the starting matrix through suitable processes, but the current conventional extraction procedures are limiting towards these possibilities. New eco-friendly, energy-efficient and effective techniques have recently gained a high interest for these purposes, due to their simplicity, shorter extraction times and reduced consumption of organic solvents. Among them, microwave-assisted extraction results particularly efficient, nowadays finding many applications 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. Maximum yield in total polyphenols of about 45 mgGAE/g, expressed as mg of gallic acid for g of starting biomass, was experimentally achieved, a promising value, thus leading to an important step forward, in the perspective of improving this waste recycling in a circular economy perspective.