Amino acid-assisted enzymatic hydrolysis of corn stover for microbial lipid production by Rhodotorula toruloides

Efficient enzymatic hydrolysis of lignocellulosic biomass (LCB) is essential for maximizing the recovery of fermentable sugars for diverse biotechnological applications. However, pretreatment by-products including lignin interact with hydrolytic enzymes, blocking their access to substrates and leading to poor monomeric sugar recovery. This study evaluated the effects of all 20 exogenous amino acids (AAs) as additives to block lignin active sites and facilitate enzyme access to polysaccharide substrates for enhanced sugar recovery. The hydrolysates were subsequently tested for microbial lipid production by Rhodotorula toruloides CGMCC 2.1389 as a model application.

The study found that most AAs enhanced enzymatic hydrolysis of 1% (w/v) H₂SO₄- and Na₂CO₃-pretreated corn stover (CS), with L-proline (Pro) increasing total reducing sugar (TRS) recovery by over 20%. Lipid production by R. toruloides on the hydrolysates was verified under single-stage and two-stage culture conditions. The lipid yield reached over 17 g/100 g TRS with some AAs, despite lower titers. Moreover, the dominance of C16 and C18 fatty acids in the lipids suggest no adverse effects of AAs on the yeast's metabolism.

Exogenous AA addition during enzymatic hydrolysis enhanced sugar recovery; however, its impact on R. toruloides lipid production varies with culture conditions, where a two-stage process with nutrient limitation could be more favorable for high lipid production. While this strategy proved to be more effective for enhanced sugar recovery, future studies are expected to uncover the underlying mechanisms that drive this improvement.