Enzymatic hydrolysis of liquefied corn starch in a membrane bioreactor

The overall objective of this project was to develop and optimize a membrane reactor for the continuous saccharification of liquefied corn starch by glucoamylase. The effects of enzyme concentration, substrate concentration and residence time on starch conversion were studied. Increasing the concentration of enzyme (AMG 200L, NOVO Laboratories) increased conversion at all substrate levels studied (1-30% w/v) up to an enzyme level of 6 g/L, but appeared to be unaffected at higher enzyme concentrations. Substrate conversions of 95% or greater were consistently obtained at substrate-to-enzyme ratios (S:E) of 25-50 w/w. Lower S:E ratios enhanced the reversion reaction and lowered the glucose content of the product stream. At equivalent substrate and enzyme concentrations, conversions were 15-22% greater as the residence time was increased from 2 to 3 hours.A residence time distribution study showed that the membrane reactor could be modelled as a continuous stirred tank reactor (CSTR). Thermal inactivation of the enzyme, membrane poisoning and mechanical shear did not have a significant effect on the long-term activity of the membrane reactor. The membrane reactor was operated for up to 30 hours at steady-state with no decrease in glucose output.A model was developed based on Michaelis-Menten kinetics coupled with a mass balance equation for a CSTR to predict the membrane reactor's performance. The key determinant of reactor performance was a modified space time parameter that included all the variables affecting the reactor performance. The model was satisfactory within the range of expected commercial operating parameters.The continuous membrane reactor developed in this project was capable of producing a glucose syrup from liquefied corn starch at much lower residence times (2-3 hours) and a higher dextrose equivalent (DE) than current commercial practice. Substrate up to 30% w/v could be processed with minimal operational problems, due to the high levels of conversion obtained in the membrane reactor. Productivities of the continuous reactor were 10 to 20 times greater than those obtained in batch reactors.U of I OnlyETDs are only available to UIUC Users without author permissio