Liquefaction Enzymes

Maize starch is the most widespread raw material used, followed by wheat, tapioca and potato. As native starch is only slowly degraded using alpha-amylases, a suspension containing 30-40% dry matter needs first to be gelatinised and liquefied to make the starch susceptible to further enzymatic breakdown. This is achieved by adding a temperature-stable alpha-amylase to the starch suspension. The mechanical part of the liquefaction process involves the use of stirred tank reactors, continuous stirred tank reactors or jet cookers. In most plants for sweetener production, starch liquefaction takes place in a single-dose, jet-cooking process. The alpha-amylase SEBstar HTL or Starzyme HT 120Lis added to the starch slurry after pH adjustment, and the slurry is pumped through a jet cooker. Here, live steam is injected to raise the temperature to 105°C, and the slurry's subsequent passage through a series of holding tubes provides the five-minute residence time necessary to fully gelatinise the starch. The temperature of the partially liquefied starch is then reduced to 90-100°C by flashing, and the enzyme is allowed to further react at this temperature for one to two hours until the required DE is obtained. The enzyme hydrolyses the alpha-1,4-glycosidic bonds in pregelatinised starch, whereby the viscosity of the gel rapidly.