VALORIZATION OF WOODY BIOMASS FOR THE PRODUCTION OF CAROTENOIDS BY MICROBIAL FERMENTATION

Carotenoids are important molecules employed as food additives for human, but also in the feed, cosmetic and pharmaceutical fields. Up to 90% of carotenoids derive from chemical manufacturing of petrochemical origin, while the remaining fraction is extracted from natural sources, mainly edible, as carrots and palm oil fruits for β-carotene. Therefore, there is an increasing need for alternative sources not in competition with the food sector. In this scenario, we developed an integrated pipeline where the naturally oleaginous and carotenogenic yeast Rhodosporidium (Rhodotorula) toruloides, thanks to its ability to metabolize both pentose and hexose sugars (typically derived from lignocellulosic biomasses), produces valuable carotenoids (e.g., β-carotene, torulene) from residual biomasses. Different types of biomasses considered residues have been deployed for the purpose. Since one of the goals of NFBC is the valorization of urban biodiversity, in this work we focused on the use of leftovers from the pruning of a public park in the metropolitan area of Milan (Lombardy, Italy). Specifically, bark (B) and wood (W) residues have been collected from mulberry trees (M) and sessile oaks (S), obtaining four different woody materials (here shortened in MTB, MTW, SOB and SOW). To the best of our knowledge, such biomasses are used here for the first time in the development of a biorefinery approach implementing microbial cell factories. The biomass is initially physically pretreated and then processed by the use of enzymatic cocktails to release sugars from the lignocellulosic matrix. The obtained hydrolysate is then deployed as a medium for the growth of R. toruloides and carotenoids production in a separate hydrolysis and fermentation (SHF) setting. The produced carotenoids are then extracted and quantified by flow-injection analysis coupled with mass spectrometry (FIA-MS), in order to evaluate differences in the amount and ratio of the obtained molecules when using different biomasses. This work shows the potential of biodiversity scouting to develop biorefineries with different outcomes, to be tailored for special market requests. Further investigations will evaluate cellular features on the yeast during the fermentation, in order to provide insights useful both for the improvement of the knowledge of metabolic pathways in R. toruloides and the optimization of carotenoids production from these woody biomasses.