Optimal dosage and recycle of cellulases for efficient biomass saccharification of cardoon and giant reed

Abstract

The deployment of sugar-based biorefineries is limited by the availability of feedstocks and by the cost of enzymes. Cynara cardunculus and Arundo donax are relevant non-food crops for the development of sugar-based biorefineries. Enzymatic hydrolysis of C. cardunculus and A. donax stalks have been optimized in terms of biocatalyst dosage and reuse. Optimal utilization of a commercial biocatalyst cocktail was achieved assessing the enzyme adsorption on the biomass slurry prior to the hydrolysis stage. The partitioning of cellulases between the liquid the substrate has been characterized for raw and pretreated biomasses. Enzyme uptakes up to 18 mg/g were recorded with 5 % biomass slurries and 0.2–3 g/L initial enzyme concentrations for both C. cardunculus and A. donax. The nearly irreversible nature of the enzyme adsorption allowed a partial recovery of the unbound biocatalyst and the polysaccharides hydrolysis by adsorbed biocatalysts. In the best condition, 89 % glucans conversion was obtained in pretreated cardoon with 4 mg/g loading of adsorbed cellulases (lower than the saturation level) and in giant reed with 13 mg/g. Notably, the residual activity of the unbound biocatalyst was sufficient to hydrolyse more than 65 and 75 % of glucans in pretreated cardoon and giant reed, respectively. The proposed method can be applied routinely to any biorefinery feedstock and both commercial and in-situ produced cocktails to minimize the enzyme dosage.