Acid hydrolysis of sucrose in sweet sorghum syrup followed by succinic acid production using a genetically engineered Escherichia coli

Abstract

Acid hydrolysis of sucrose was studied as a method to convert sucrose in sweet sorghum syrup into glucose and fructose before fermentation with the genetically engineered succinic acid-producing Escherichia coli strain AFP184. Successful hydrolysis of sucrose in sweet sorghum syrup was achieved without noticeable formation of degradation products using moderate temperatures, 65–85 °C, with 0.24–0.48 M HCl in less than 30 min. The measured sucrose hydrolysis rates were lower than previously reported for sweet sorghum molasses. The E. coli strain AFP184 consumed all the sugars (glucose and fructose) in the sweet sorghum syrup hydrolysate. The products were predominately succinic and acetic acid. The final concentration of succinic acid was 27 g/L, but the organism was shown to produce higher levels of succinic acid (60 g/L), when grown under optimal conditions on pure glucose. Note that the fermentation results during scale-up should be seen as preliminary, as initial sugar content, aeration, agitation, and duration of initial aerobic growth phase were not optimized. Thus, improved results closer to those experienced with glucose are expected.