Chemical characterization and biological activities of spent coffee ground and coffee silverskin: possible reuse as nutraceuticals and ingredients for fertilizer products

Worldwide, around 10 million tons of coffee are consumed each year, producing many tons of coffee by-products such as spent coffee grounds (SCG) and coffee silverskin (CS). Therefore, various applications have been proposed for SCG and CS valorisation, as they are a good source of nutrients and bioactive compounds such as soluble dietary fibre, protein, minerals, fat, caffeine and polyphenols [1-4]. In our research group, the two matrix have been fully chemically characterize in terms of polyphenols, fat and fatty acid profile, volatiles, cholesterol-lowering phytosterols, and vitamins [1-4]. For the first time the content of polyphenols and phytosterols have been monitored also in all the coffee production chain, starting from green coffee, to CS, roasted coffee, SCG and espresso coffee to have a complete view of theirs evolution. From a biological point of view, the most interesting results are on SH-SY5Y cells that showed a higher effectiveness of CS and SCG extracts in protecting cells against H2O2-induced oxidative stress by upregulating endogenous antioxidant enzymes such as thioredoxin reductase, heme-oxygenase 1, NADPH quinone oxidoreductase, and glutathione reductase. The water extract of CS and SCG were the most effective in counteracting lipopolysaccharide-induced neuroinflammation in microglial BV-2 cells by strongly reducing the expression of proinflammatory mediators through the modulation of the TLR4/NF-κB pathway. Moreover, the hydroalcoholic and methanolic SCG and CS extracts were shown to be the most active against all selected enzymes such as tyrosinase, α-glucosidase, α-amylase and α-cholinesterases. CS and SCG are rich in fibres, lipids, alkaloids, nitrogen compounds, minerals, polyphenols and these residues are potentially useful in the context of fertilization. The fertilizer formulation was carried out using all compounds of natural origin to improve the C/N ratio by means of a wet granulation process. Once obtained, the fertilizer was used to grow salad seedlings inside a climatic chamber and after 12 weeks, a 20% improvement in seedling growth and an increase in leaf area was achieved. The nutritional composition of salad growth with the help of fertilizer and non treated one will be studied.