Study on effects of addition of glycerol on the production of succinic acid by fermentation on Napier grass hydrolysate using an Actinobacillus succinogenes mutant

• Main Authors: LEE, JHIH-SING, 李志興
• Other Authors: LEE, WEN-CHIEN
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/9m3ty2

碩士 === 國立中正大學 === 化學工程研究所 === 106 === In order to reduce the emissions of the greenhouse gases and the global temperature, the use of biomass as the raw material to produce chemical and biofuel becomes a trend in most countries. Lignocellulosic feedstock like Napier grass has a great potential to be chosen as a raw material for renewable energy and biochemical production. Succinic acid is a C4 platform chemical and widely used in food, chemical and medical industry. In the recent years, as the expansion of its applications, succinic acid becomes highly demanded in the global market. In this study, we used Napier grass as the source of biomass. After alkali pretreatment, Napier grass was subjected to hydrolysis with cellulosic enzymes to gain the hydrolysate which was rich of glucose and xylose. The hydrolysate was then used as the carbon source for the production of succinic acid. When the hydrolysate of pretreated Napier grass was used as the carbon source, the fermentation by the A. succinogenes mutant resulted in producing 0.59±0.02 g succinic acid per unit gram of reducing sugar. This succinic acid yield is lower than that using glucose or glycerol as the carbon source. Also, the yield of acetic acid reached to 0.30±0.04 g/g, resulting in the reduction of the ratio of succinic acid to acetic acid (S/A) to 2.00 ± 0.20. Compare with glucose and xylose, glycerol can generate more reducing power. We hope the addition of glycerol to the medium could increase the yield of succinic acid and reduce the production of acetic acid. However, the results show that the yield of succinic acid was almost equal to the succinic acid yield contributed by all the components of the carbon source. No substantial increase in the yield of succinic acid was found and the yield of acetic acid could not be reduced. On the other hand, the fermentation time was prolonged as the proportion of additional glycerol increased; thus the productivity was also decreased. However, when the ratio of hydrolysate to glycerol is 10:1, the productivity was significantly improved. Compared with sole use of hydrolysate as the carbon sources, the addition of high-reducing-power glycerol at the ratio of 10:1 could promote the productivity of succinic acid from 0.79 ± 0.07 g/L/h to 0.84 ± 0.10 g/L/h. This result can be inferred from metabolic pathways of Actinobacillus succinogenes. When xylose was used as the carbon source, the ATP was consumed much more than the use of glucose or glycerol as the carbon source. The acetic acid was generated to match the additional ATP requirement to metabolite xylose. Because of the presence of xylose, the formation of acetic acid could not be reduced even with the addition of glycerol. Finally, compared with the fermentation on sole xylose, the fermentation on hydrolysate resulted in a slightly increase in acetic acid production, suggesting that besides xylose some unknown inhibitors in the hydrolysate could cause the formation of acetic acid.