Research progress on the biosynthesis of D-lactic acid from low-value biomass materials

D-Lactic acid (D-LA) is an important biomolecule with a wide range of applications, which can be produced from renewable biomass resources by fermentation. To date, various biological techniques have been explored to improve D-LA production from biomass materials. However, there are still many challenges for fermentative DLA production stemming from the poor optical purity, low yield, and difficulties in final product separation. This paper takes an overview of the recent trends and advances in engineered strains with carefully orchestrated metabolic pathways for bio-based D-LA production. A specific emphasis is given to the construction of the D-LA process including the sugars platform, fermentation unit, and the separation and purification systems. Moreover, the recent technical trends in the production of poly (3-hydroxybutyrate-co-lactate), the bio-based polymer by engineered strains, and the emerging techniques for the transformation of CO2 into D-LA production were also discussed. D-LA's future lies in establishing innovative sustainable approaches by utilizing the inexpensive biomass substrates and the hyper-engineered strains, combined with efficient fermentation coupled with separations for high optical purity products, which are imperative to the overall economic feasibility.