Glucose Syrup | production of high fructose syrup

Glucose syrup is a concentrated aqueous solution of glucose maltose and other nutritive saccharides from edible starch. Glucose or dextrose sugar is found in nature in sweet fruits such as grapes or honey. It is less sweet than sucrose (cane sugar). Glucose syrup is used in large quantities in fruits, liquors, crystallized fruits, bakery products, pharmaceuticals, and brewery products.

Production of glucose syrup Glucose syrup production from cassava can be subdivided into the following process areas of liquefaction, saccharification, and purification.

Native starch consists of microscopic granules having a complex internal structure. At room temperature, these granules are insoluble in water. However, if a starch slurry is heated above 60 oC, the granules will swell and eventually rupture. This results in a dramatic increase in viscosity. At this point, the starch has been “gelatinized”. The gelatinized starch is now susceptible to attack by amylase enzymes. In practice, cassava starch in gelatinized and partially hydrolyzed very rapidly in one step (see flow chart) by heat-stable amylase. This step is called liquefaction. The partially degraded starch chains called dextrins are suitable starting materials for the later steps in syrup production.

Liquefaction

A starch slurry is made with 30-35% dry solids and its pH is adjusted to 6.0-6.4. Calcium is added using calcium hydroxide or calcium chloride. Calcium ions stabilize the enzyme. A heat-stable a-amylase (Novo’s Termamyl 120L) is mixed into the slurry, then the slurry is instantaneously heated to 100 oC and held at this temperature for 10 min before it is cooled to 90 oC. This temperature is maintained for 1-3 h to further hydrolyze the starch.

At the end of this step, the starch has been converted to dextrins with a dextrose equivalent (DE) between 8 and 15. (The physical properties of the syrup vary with the DE and the method of manufacture.) DE is the total reducing sugar in the syrup expressed as dextrose on a dry weight basis.

Saccharification

After liquefaction, the pH is reduced to between 4.2 and 4.5 and the solution is cooled to 60 oC. A glucomylase (Novo’s AMG 300L) is added immediately. The reaction time for saccharification is usually between 24-48 h depending on enzyme dose. Glucoamylase releases single glucose units from the ends of dextrin molecule. Syrups of 95% glucose or higher are manufactured, e.g., a typical 98 DE syrup could have the sugar profile as shown in the flow chart.