Multistage optimization of corn stover valorization for enhanced docosahexaenoic acid production via Schizochytrium limacinum fermentation

The valorization of lignocellulosic agricultural residues into high-value nutraceuticals, such as docosahexaenoic acid (DHA), represents a crucial advancement in sustainable biorefinery processes. While previous studies have predominantly focused on glucose utilization from hydrolysates for microbial product biosynthesis, the implications of residual enzymatic hydrolysis buffers—specifically sodium acetate and citrate—on microbial fermentation remain unexplored. This study systematically optimized the processing of corn stover for hydrolysate preparation. The resulting hydrolysate, which contains both glucose and acetate/citrate, was utilized for biological DHA synthesis through fermentation of Schizochytrium limacinum . NaOH-pretreated corn stover demonstrated enhanced digestibility, yielding 332.8 g glucose/kg biomass through optimized enzymatic hydrolysis. Fed-batch hydrolysis with 20% (w/v) solid loading achieved 81.0 g/L glucose concentration while maintaining 80.9% conversion efficiency. Comparative fermentation studies revealed that sodium acetate-buffered hydrolysates supported superior biomass accumulation (17.4 g/L) compared to citrate-buffered systems (16.8 g/L), both significantly exceeding control. Lipid analysis demonstrated that acetate-mediated cultivation induced maximal lipid accumulation at 58.3%, with DHA representing 26.9% of total fatty acids. Although relative DHA content showed moderate reduction, absolute titer reached 2.7 g/L through enhanced lipid biosynthesis. This multistage optimization framework establishes an efficient platform for lignocellulosic DHA production while providing new insights into buffer component effects on lipid metabolism.