Exploitation of cardoon roots inulin for polyhydroxyalkanoate production

Cynara cardunculus, cardoon, is a biorefinery crop with an overwhelming role in the bioplastic scenario. This work explored the use of inulin extracted from cardoon roots as a feedstock for polyhydroxyalkanoates (PHA) production. Cardoon roots from both spring and winter seasons were subjected to two protocols consisting of an autoclave extraction followed by i) an ethanol precipitation and further lyophilization or ii) lyophilization directly. The resulting extracts were characterized for recovery yield (from 11.6 to 16 g of inulin per 100 g of roots), purity grade (from 64% to 97%) and molecular weight distribution, the latter being affected by both seasonal variability and the extraction method. The performances of two PHA producers, Cupriavidus necator and Burkholderia cepacia, were compared in Simultaneous Saccharification and Fermentation of spring inulin extracts obtained with the two protocols, exploring the effect of controlled addition of fungal inulinase PlaI. Up to 2 g/L of polyhydoxybutyrate (PHB) polymer was produced in the best feeding condition, with both strains found able to metabolize the main phenolic acids coextracted with inulin. Diversity in polymer yields were observed, with evidence of the synthesis of PHB polymers characterized by different molecular weight distributions depending on the type of feeding and microorganism employed. The proposed processes are placed in the frame of the circular economy approaches applied to the valorization of cardoon biomass in the bioplastic field.