Optimization of down-stream for cellulases produced under solid-state fermentation of coffee husk

This work systematically studies the downstream process of the solid state fermentation (SSF) of a mixture of coffee husk and wood chips, inoculated with compost, for cellulase production. Downstream of SSF (at pilot scale) remains as one of the less studied stages of the process, being critical in technical, environmental and economic terms. In this study, the specific downstream points considered were: (i) enzyme extraction yield, in terms of extraction ratio solid:solvent, agitation mode and solvent type; (ii) enzymatic activity recovery of the lyophilised extract and (iii) efficiency of consecutive extractions. Results indicate a maximum activity recovery of 108 ± 30% in the extraction performed at ratio 1:5 solid-solvent, in static mode and with distilled water. Statistical analysis revealed a high dispersion of the results and needs to be considered to extract consistent conclusions in any downstream of SSF. Lyophilisation demonstrated to be an adequate technology for enzymatic activity preservation. Regarding consecutive extractions, yield recovery in the first and second extraction maintain a similar value. In a framework of a zero-waste enzyme production process, different strategies have been tested for the remaining solid after extraction. Respirometric tests reveal that it is possible to aerobically stabilize the remaining solid obtaining a compost like material, whereas anaerobic digestion resulted in low methane yields (51 ± 3 mL methane g−1 VS)