Fermentation of Enzymatic Hydrolysate from Hydro-organo Pretreated Eucalyptus Globulus to Carotenoids and Triglycerides by the Red Yeast Rhodosporidium Toruloides

The transition towards a circular bioeconomy demands the integration of efficient lignocellulosic biomass pretreatment with a high-performing cell factory. In this study, Eucalyptus globulus residues were valorised through a sequential process combining an innovative hydro-organo pretreatment and enzymatic hydrolysis to efficiently release second-generation fermentable sugars. The resulting hydrolysate, rich in glucose and xylose, was subsequently employed as a carbon source for the oleaginous red yeast Rhodosporidium toruloides DSM 10134. Process optimisation, with particular emphasis on the carbon-to-nitrogen (C/N) ratio, enabled the coproduction of microbial oil and high-value carotenoids. Under the optimised process conditions, enzymatic hydrolysis reached 99 mol% and 95 mol% for glucose and xylose, respectively. Notably, at a C/N ratio of 60 g g-1, R. toruloides exhibited promising performance, achieving oil titers of 7.4 g L-1 alongside carotenoid production of 194 mg L-1. These findings highlight the potential of integrating chemical and biological processes to drive the transition towards a circular bioeconomy.