Saccharification Enzymes

When maltodextrins are saccharified by further hydrolysis using glucoamylase (SEBamyl GL) or fungal alpha-amylase, a variety of sweeteners can be produced. These have dextrose equivalents in the ranges 40-45 (maltose), 50-55 (high maltose), and 55-70 (high conversion syrup). By applying a series of enzymes including beta-amylase (SEBmalt BA), glucoamylase and pullulanase as debranching enzymes, intermediate-level conversion syrups with maltose contents of nearly 80% can be produced. A high yield of 95-97% glucose may be produced from most starch raw materials (maize, wheat, potatoes, tapioca, barley and rice).

Under industrial conditions, the equilibrium point is reached when the level of fructose is 50%. The reaction also produces small amounts of heat that must be removed continuously. To avoid a lengthy reaction time, the conversion is normally stopped at a yield of about 45% fructose. The isomerisation reaction in the reactor column is rapid, efficient and economical if an immobileised enzyme system is used. The optimum reaction parameters are a pH of about 7.5 or higher and a temperature of 55-60°C. These parameters ensure high enzyme activity, high fructose yields and high enzyme stability. However, under these conditions glucose and fructose are rather unstable and decompose easily to organic acids and coloured by-products. This problem is countered by minimising the reaction time in the column by using an immobilised isomerase in a column through which the glucose flows continuously.

The enzyme granulates are packed into the column but are rigid enough to prevent compaction. The immobilised enzyme loses activity over time. Typically, one reactor-load of glucose isomerase is replaced when the enzyme activity has dropped to 10-15% of the initial value. The most stable commercial glucose isomerases have halflives of around 200 days when used on an industrial scale. To maintain a constant fructose concentration in the syrup produced, the flow rate of the glucose syrup fed into the column is adjusted according to the actual activity of the enzyme. Thus, towards the end of the lifetime of the enzyme, the flow rate is much slower. With only one isomerisation reactor in operation, there would be great variation in the rate of syrup production over a period of several months.