Starch hydrolysis under low water conditions: a conceptual process design

A process concept is presented for the hydrolysis of starch to glucose in highly concentrated systems. Depending on the moisture content, the process consists of two or three stages. The two-stage process comprises combined thermal and enzymatic liquefaction, followed by enzymatic saccharification. The three-stage process starts with shear induced melting of starch, followed by enzymatic liquefaction and saccharification. At a low moisture content, the shear stress needed to completely melt corn starch is so high that significant enzyme inactivation cannot be avoided, which leads to a need for separating starch melting and liquefaction in two separate processing steps. Assuming the use of currently available enzymes, the final product composition was estimated to contain 69-93% glucose, starting with respectively 65% and 35% dry starch. These results showed that the formation of side-products, mainly isomaltose and isomaltotriose, increased with increasing dry matter content. Increasing the dry matter content from 35% to 65% resulted in increasing reactor productivity of 17%, while the amount of water that should be removed from the system was reduced by 87%. (c) 2005 Elsevier Ltd. All rights reserved