Green valorisation of defatted waste of Cynara cardunculus L. to single cell oil and high-quality lignin

In recent years a growing interest has been directed to 3rd-generation biomass, such as the infesting plant species Cynara cardunculus (cardoon). It is a very common variety in the center of Italy and in the Mediterranean region. Cardoon offers a wide spectrum of potential applications, being a rich source of fibers, oil and bioactive compounds. The cultivation of this perennial herbaceous biomass shows significant advantages, such as good adaptability to climate change and growth on marginal or uncultivated lands with modest inputs, including moderate irrigation and minimal need of nutrients. The seeds of the flower are exploited for oil production for food and bio-diesel supply chains. The nonedible lignocellulosic residues can undergo pretreatments that favour further exploitation of this biomass [1,2]. In this study, the steam exploded defatted cardoon was used as feedstock for the production of sugars-rich hydrolysates by enzymatic hydrolysis. Two different commercial enzymatic mixture Cellic® CTec2 and Cellic® CTec3 were tested at different dosages (15, 30, 45 FPU/g glucan) and in the presence of different biomass loadings (2, 5, 10 wt%). The hydrolysates obtained under optimised reaction conditions (Cellic® CTec3, 30 FPU/g glucan, 2 or 5 wt% biomass loading, 72 h) were then fermented to new generation oil by the two oleaginous yeasts Lipomyces starkeyi DSM 70296 and Cryptococcus curvatus DSM 70022. The lipid contents of 45 and 60 wt% and the lipids yields of 20 and 24 wt% were reached, respectively. The single cell oils profile was similar to that of food oils usually employed for the production of biodiesel. Finally, in order to valorise all the fractions of cardoon, a green extraction protocol was optimised in order to recover high quality organosolv lignin from exploded cardoon suitable for material applications such as dielectric for organic thin film devices and bio-based component for functional coatings (Fig. 1). Different green solvents were tested, such as EtOH, EtOH:NH3 1:1, EtOH:H2O 1:1, MeTHF, MeTHF:EtOH:NH3 1.6:0.2:0.2, in an orbital shaker at 55 °C, 90 min, 50 g/L biomass loading, agitation speed 250 rpm. The lignin yield extracted by EtOH, EtOH:NH3 and MeTHF was around 10 wt% respect to the exploded cardoon and around 30% respect to the lignin content. Figure 1 – Schematic representation of the implemented biorefinery scheme. 1. Raspolli Galletti, A. M., Licursi, D., Ciorba, S., Di Fidio, N., Coccia, V., Cotana, F., Antonetti, C. Catalysts, 2021, 11, 1082-1100. 2. Di Fidio, N., Antonetti, C., Raspolli Galletti, A. M. Proceeding 29th EUBCE, 2021.