This presumably was due to the transportation
rate of glucose was faster than that of glycerol in R. arrhizus.
Therefore, in the co-fermentation, when glucose existed, R.
arrhizus could assimilate glucose rapidly for growth and fumaric
acid production, and higher biomass could be obtained when glucose
was depleted. Under higher biomass, the assimilation of glycerol
might be accelerated. As a consequence, the fumaric acid
production was enhanced finally. Although the production of
fumaric acid in co-fermentation was a little lower than that in glucose
fermentation (80 g/L), the price of crude glycerol was far less
than glucose, indicating that the co-fermentation strategy might
provide a more cost-effective way for fumaric acid fermentation.
Currently, the price of crude glycerol (20%, Jiangsu Kate New Energy Co., Ltd, China) in Chinese market is about CNY300/t, while
the glucose (90%, Jinan Guoshi Weiye Chemical Co., Ltd, China) is
CNY3200/t. By the co-fermentation, glycerol could partly replace
glucose for fumaric acid production, and the production cost of
fumaric acid (based on the cost of the carbon source input) was
reduced by approximately 14% as compared to the fermentation
using glucose (80 g/L) as carbon source.