Combined antioxidant-biofuel production from coffee silverskin.

Biorefinery concept asks for an integrated processing approach to exploit all biomass components. The self-sustainability target may be approached if molecules characterized by high added value and fermentable sugars are produced simultaneously. In the present study, sequential (i) mild hydrothermal pretreatment to produce antioxidants and (ii) NaOH pretreatment to produce a fermentable sugar solution were carried out on coffee silverskin. Twenty-minute treatment and biomass to liquid ratio 1:30 (g mL-1 ) were identified as optimal operating conditions to extract bioactive compounds characterized by antioxidant activity (22.2 mgGAE /gCSS ; 13.9 mgTE /gCSS ). Twenty-minutes and biomass to liquid ratio of 1:20 (g mL-1 ) were identified as optimal operating conditions to maximize sugar recovery and ABE production (solvent yield YABE/Sugars and ABE productivity of 0.21 g g-1 and 0.12 g L-1  h-1 were obtained, respectively). The study marks the highly economic potential of the process aimed to exploit the CSS as feesdstock for antioxidant and biofuel production.