Optimization of antioxidants extraction from coffee silverskin, a roasting by-product, having in view a sustainable process

• Silverskin, a coffee roasting by-product, is a source of natural antioxidants.
• Solvent, temperature and time highly affected the antioxidants extraction yields.
• Flavonoids, tannins and total phenolics contents of extracts were determined.
• Antioxidant activity of extracts was determined using two complementary methods.
• The use of a hydroalcoholic mixture (1:1) at 40 °C for 60 min provided the best extraction yields.

Coffee silverskin is a major roasting by-product that could be valued as a source of antioxidant compounds. The effect of the major variables (solvent polarity, temperature and extraction time) affecting the extraction yields of bioactive compounds and antioxidant activity of silverskin extracts was evaluated. The extracts composition varied significantly with the extraction conditions used. A factorial experimental design showed that the use of a hydroalcoholic solvent (50%:50%) at 40 °C for 60 min is a sustainable option to maximize the extraction yield of bioactive compounds and the antioxidant capacity of extracts. Using this set of conditions it was possible to obtain extracts containing total phenolics (302.5 ± 7.1 mg GAE/L), tannins (0.43 ± 0.06 mg TAE/L), and flavonoids (83.0 ± 1.4 mg ECE/L), exhibiting DPPH scavenging activity (326.0 ± 5.7 mg TE/L) and ferric reducing antioxidant power (1791.9 ± 126.3 mg SFE/L). These conditions allowed, in comparison with other “more effective” for some individual parameters, a cost reduction, saving time and energy.