Inhibitors derived from wheat straw hydrolysate can affect the production of succinic acid by Actinobacillus succinogenes

Abstract

Lignocellulosic biomasses are promising source of fermentative sugars for the production of succinic acid. The lignocellulosic matrix must be pretreated to make the sugars available for the fermentation, but the most tested operative conditions can generate inhibitors as acetic acid, furans, phenolic compounds. Inhibitors remained an obstacle for the implementation of succinic acid production starting from recalcitrant biomasses as wheat straw. Batch tests were performed at two starting concentrations of strain, sugars (glucose, glucose and xylose) and inhibitors (acetic acid and furfural) by comparing the fermentation in standard broth medium and hydrolysate. Notwithstanding the presence of acetic acid (52.5 mg/L) and furfural (15 mg/L), succinic acid was obtained at 9*10⁻² ± 7*10⁻³ g/L by starting from wheat straw hydrolysate that contained glucose (1.1 g/L), xylose (0.4 g/L) and without additional nitrogen source. Therefore, the study highlighted that a more concentrated inoculum was able to reduce the synergistic effect of inhibitors at their highest concentrations. The results obtained may contribute to improve succinic acid production from the biomasses that have been under-exploited but abundantly available, as wheat straw, for which solutions must be found to solve the problem of inhibitors production or to mitigate its effect on the fermentation process.