Pu Zheng

Fermentative production of succinic acid from straw hydrolysate by Actinobacillus succinogenes

In this work, straw hydrolysates were used to produce succinic acid by Actinobacillus succinogenes CGMCC1593 for the first time. Results indicated that both glucose and xylose in the straw hydrolysates were utilized in succinic acid production, and the hydrolysates of corn straw was better than that of rice or wheat straw in anaerobic fermentation of succinic acid. However, cell growth and succinic acid production were inhibited when the initial concentration of sugar, which was from corn straw hydrolysate (CSH), was higher than 60 g l(-1). In batch fermentation, 45.5 g l(-1) succinic acid concentration and 80.7% yield were attained after 48 h incubation with 58 g l(-1) of initial sugar from corn straw hydrolysate in a 5-l stirred bioreactor. While in fed-batch fermentation, concentration of succinic acid achieved 53.2 g l(-1) at a rate of 1.21 g l(-1) h(-1) after 44 h of fermentation. Our work suggested that corn straw could be utilized for the economical production of succinic acid by A. succinogenes.

Succinic acid production from corn stover by simultaneous saccharification and fermentation using Actinobacillus succinogenes

Simultaneous saccharification and fermentation (SSF) technique was applied for succinic acid production by Actinobacillus succinogenes in a 5-l stirred bioreactor with corn stover as the raw material. The process parameters of SSF, including corn stover pretreatment condition, substrate concentration, enzyme loading and fermentation temperature were investigated. Results indicated that pretreating corn stover with diluted alkaline was beneficial for the succinic acid production, and succinic acid yield could be significantly increased when adding the cellulase supplemented with cellobiase. The maximal succinic acid concentration and yield could reach 47.4 g/l and 0.72 g/g-substrate, respectively. The corresponding operation conditions were summarized as follows: SSF operation at 38 °C for 48 h, diluted alkaline pretreated corn stover as substrate with concentration of 70 g/l, enzyme loading of 20FPU cellulase and 10 U cellobiase per gram substrate. This result suggested an industrial potential of succinic acid production by using SSF and corn stover.

Highly efficient biosynthesis of sucrose-6-acetate with cross-linked aggregates of Lipozyme TL 100 L

As a short chain monoester, sucrose-6-acetate (S-6-a) is a key intermediate in the preparation of an eminent sweetener (sucralose). To replace the traditional multi-step chemical route for sucralose biosynthesis, enzymatic synthesis of S-6-a was investigated, using cross-linked enzyme aggregates (CLEAs) of Lipozyme TL 100 L. The optimal CLEA preparation conditions was obtained as follows: using 33.3% (v/v) PEG600 co-precipitated with additive of D-sorbierite, then cross-linking with 1.5% (v/v) glutaraldehyde at 0 °C for 4 h. As a result, the immobilized Lipozyme had high specific bioactivity (34.64 U/g) of transesterification in non-aqueous media. With these immobilized enzymes, the optimum transesterification conditions were investigated systematically, including CLEA loading, the mole ratio of vinyl acetate versus sucrose, temperature and reaction time, etc. The results showed that the highest concentration and yield of S-6-a was 49.8 g/L and 87.46%, respectively. Further experiments showed that the resulting CLEAs also had much higher operational stability than the commercial Lipozyme TLIM. The present work has paved a new path for the large-scale bioproduction of S-6-a with immobilized lipase in the future.