Highly efficient consolidated bioprocessing of starch-rich raw wet herbal extraction residues into single cell oil by oleaginous yeast Lipomyces starkeyi.

The valorization of herbal extraction residues (HERs) into biofuels and chemicals is critical to the sustainable development of the traditional Chinese medicine industry. In this study, four starch-rich powdered HERs, namely Radix isatidis residue (RIR), Radix paeoniae alba residue (RPAR), Kudzu root residue (KRR), and Ginkgo biloba residue (GBR), were directly converted into single cell oil (SCO) by the oleaginous yeast Lipomyces starkeyi via consolidated bioprocessing (CBP) for the first time. The CBP strategy outperformed the conventional separate hydrolysis and fermentation (SHF) approach, featuring substantially simplified procedures and achieving 33.46%-87.42% higher SCO production. Notably, raw wet HERs could also be directly utilized for efficient SCO production via CBP, and supplementation with a small amount of cellulase further enhanced SCO production significantly. When L. starkeyi was directly cultured in 100 g/L raw wet RIR, RPAR, KRR, and GBR with the addition of 1 FPU/g cellulase, the final SCO titers reached 11.90 g/L, 12.20 g/L, 13.90 g/L, and 17.65 g/L, respectively. Fatty acid composition analysis and biodiesel property assessment confirmed that these SCOs were promising substitutes for biodiesel production. This study proposes a highly integrated process for direct SCO production from raw wet HERs. The strategy significantly streamlines the operational workflow by eliminating energy-intensive drying, mechanical size reduction and separate pretreatment and enhances SCO production, holding great potential to improve the economic performance of the HERs-to-SCO conversion route.