Production of L-malic acid from sugarcane molasses using Aspergillus niger

Sugarcane molasses is a viscous waste liquid produced after the refining of sugarcane juice. The effective utilization of sugarcane molasses has significant potential for producing compounds by microorganisms. This study explored the influences of different carbon sources on the L-malic acid titer of A. niger , identifying sucrose as the optimal carbon source. Based on this, the sucB gene encoding sucrose hydrolase was overexpressed, and the engineered strain A. nige r RG0081 was constructed for effective producing the L-malic acid from sucrose. To further reduce costs, sugarcane molasses was used instead of sucrose. Additionally, the fermentation conditions of A. nige r RG0081 were optimized using response surface analysis to determine the optimal concentrations of sugarcane molasses, peptone, K 2 HPO 4 , and MgSO 4 ·7 H 2 O. Finally, fermentation of RG0081 was conducted in a 5-L fermenter, the titer of L-malic acid reached 110.72 ± 1.21 g/L. Our investigation provides a low-cost approach for the conversion of sugarcane molasses into L-malic acid. • First engineered strain of A. niger for efficient L-malic acid production from sugarcane molasses, reducing substrate costs compared to glucose-based systems. • Overexpression of sucB enhanced sucrose hydrolysis efficiency by 2.1-fold, enabling 110.72 g/L L-malate titer in a 5-L fermenter. • Sustainable valorization of sugarcane waste offers a scalable and eco-friendly alternative to petroleum-derived malic acid synthesis.