Highly efficient enzymatic hydrolysis and lipid production via Cutaneotrichosporon oleaginosum from alkaline deep eutectic solvent pretreatment of corn stover

Biomass recalcitrance has been widely recognized as one of the major barriers to the successful commercialization of lignocellulosic biofuels. In this study, an alkaline choline chloride-glycerol deep eutectic solvent (DES) pretreatment of corn stover (CS) was proposed, which could efficiently disrupt the recalcitrant structure and achieve high monomeric sugar yield. Three independent variables (temperature, time, and NaOH dosage) were optimized by response surface methodology. Under the optimal pretreatment conditions (143 °C, 2.25 h, 1.06 wt% NaOH), the maximum monomeric sugar yield of pretreated CS reached 90.48% via enzymatic hydrolysis. The recycled pretreatment solution was used for four pretreatment cycles with comparable sugar yields. Pretreated CS exhibited distinct structural differences from raw CS, with Fourier transform infrared spectroscopy (FTIR) showing a marked reduction in lignin-related groups, X-ray diffraction (XRD) revealing a sharp increase in cellulose crystallinity from 35.51% to 70.28%, and scanning electron microscopy (SEM) displaying a loose, rough, porous structure. Fed-batch saccharification of the pretreated CS achieved a high solids loading of 61% (w/v) with 355.1 g/L of total sugars. Fed-batch culture of the liquid hydrolysate by Cutaneotrichosporon oleaginosum resulted in high dry cell weight (DCW), lipid concentration, and productivity of 61.8 g/L, 40.4 g/L, and 0.34 g/L/h, respectively. The lipid sample was dominated by C16–C18 fatty acids, indicating favorable biodiesel properties that conformed to EN 14214 and ASTM D6751 standards. This strategy provides a promising lignocellulose-to-lipid route, which facilitates the commercial success of micro-biodiesel production from inexpensive lignocellulosic materials. • Alkaline ChCl:Gly DES was described highly-efficient for corn stover pretreatment. • Response surface optimization realized a high monomeric sugar yield of 90.48%. • The high enzyme susceptibility was revealed by the physicochemical characteristics. • Fed-batch hydrolysis and fermentation realized high-density lipid production. • Microbial lipid from fed-batch culture showed high-quality biodiesel properties.