Platform molecule from sustainable raw materials; case study succinic acid

Hydrolysis of lignocellulose to succinic acid: a review of treatment methods and succinic acid applications

Succinic acid (SA) is an intermediate product of the tricarboxylic acid cycle (TCA) and is one of the most significant platform chemicals for the production of various derivatives with high added value. Due to the depletion of fossil raw materials and the demand for eco-friendly energy sources, SA biosynthesis from renewable energy sources is gaining attention for its environmental friendliness. This review comprehensively analyzes strategies for the bioconversion of lignocellulose to SA based on the lignocellulose pretreatment processes and cellulose hydrolysis and fermentation principles and highlights the research progress on acid production and SA utilization under different microbial culture conditions. In addition, the fermentation efficiency of different microbial strains for the production of SA and the main challenges were analyzed. The future application directions of SA derivatives were pointed out. It is expected that this research will provide a reference for the optimization of SA production from lignocellulose.

Isolation and screening of microorganisms for high yield of succinic acid production

This study involves the isolation of succinic acid (SA)-producing microorganisms from different samples, including the rumen, sludge, soil, and wastewater. For primary screening, 29 isolates exhibited a zone of clearance around the colony, indicating acid production. For secondary screening using thin-layer chromatography, only two isolates symbolized SA production according to their R_f values. These two isolates were further identified as Bacillus velezensis and Enterococcus gallinarum by phylogenetic analysis using the neighbor-joining method. The high SA concentrations of 50.2 and 66.9 g/L were produced by B. velezensis and E. gallinarum with an SA yield of 0.836 and 1.12 g/g glucose, respectively. The high SA concentration from these newly isolated strains was achieved with a low formation of unwanted acids compared with those from Actinobacillus succinogenes ATCC 55618. Moreover, E. gallinarum was cultured in palm oil mill wastewater (POMW) and molasses, which were cheap substrates. The high SA production of 73.9 g/L with low other acids (the ratio of SA to total acids = 0.917) was achieved using POMW and molasses (80:20) as substrates.

Well Knowledge of the Physiology of Actinobacillus succinogenes to Improve Succinic Acid Production

The anaerobic fermentation of glucose and fructose was performed by Actinobacillus succinogenes 130Z in batch mode using three different volume of bioreactors (0.25, 1 and 3 L). The strategy used was the addition of MgCO3 and fumaric acid (FA) as mineral carbon and the precursor of succinic acid, respectively, in the culture media. Kinetics and yields of succinic acid (SA) production in the presence of sugars in a relevant synthetic medium were investigated. Work on the bench scale (3 L) showed the best results when compared to the small anaerobic reactor’s succinic acid yield and productivity after 96 h of fermentation. For an equal mixture of glucose and fructose used as substrate at 0.4 mol L−1 with the addition of FA as enhancer and under proven optimal conditions (pH 6.8, T = 37 °C, anaerobic condition and 1% v/v of biomass), about 0.5 mol L−1 of SA was obtained, while the theoretical production of succinic acid was 0.74 mol L−1. This concentration corresponded to an experimental yield of 0.88 (mol-C SA/mol-C sugars consumed anaerobically) and a volumetric productivity of 0.48 g-SA L−1 h−1. The succinic acid yield and concentration obtained were significant and in the order of those reported in the literature.