Continuous enzymatic liquefaction of starch for saccharification

Abstract

A process was explored for continuous enzymatic liquefaction of corn starch at high concentration and subsequently saccharification to glucose. The process appears to be quite efficient for conversion of starch to glucose and enzymatic liquefaction and should be readily adaptable to industrial fermentation processes. Preliminary work indicated that milled corn or other cereal grains also can be suitably converted by such a process. Essentially, the process involved incorporation of a thermostable, bacterial alpha-amylase for liquefaction and, subsequently, of a glucoamylase into the continuous mixer under conditions conductive to rapid enzymatic hydrolyses. Also studied was the effect on substrate liquefaction of variable such as starch concentration (40-70 degrees ), level of alpha-amylase (0.14-0.4%, dry starch basis), temperature (70-100 degrees C), pH (5.8-7.1), and residence time (6 and 12 min). The degree of liquefaction was assessed by determining (1) the Brookfield viscosity, (2) the amount of reducing groups, and (3) the rate and extent of glucose formed after glucoamylase treatment. Best liquefaction process conditions were achieved by using 50-60% starch concentration, at 95 degrees C, with 0.4% alpha-amylase, and a 6-min residence period in the mixture. Under these conditions, rate and extents of glucose obtained after glucoamylase treatment approached those obtained in longer laboratory batch liquefactions. The amount of glucose formed in 24h with the use of 0.4% glucoamylase was 86% of theory after a 6-min continuous liquefaction, compared to 90% for a 30-min laboratory batch liquefaction (95 degrees C, 0.4% alpha-amylase).