The discovery of glucose syrup was made during the Napoleonic wars when Europe was suffering from a naval blockade by the British. A lack of sugar from the West Indies inspired many a chemist to look for ways of synthesizing a sweet alternative.
An overview
Glucose syrups, often called glucose or corn syrups in the USA, are products obtained by the hydrolysis of starch. They contain varying amounts of glucose monomer, dimer, oligosaccharides, and polysaccharides, depending on the syrup and the manufacturing process. Some products may contain very little glucose and may not even be made from corn. Additionally, reversion products, which are other sugars produced during manufacture, may be present in small amounts and can cause off-flavors. Glucose syrup is a purified concentrated aqueous solution of nutritive saccharides obtained from starch. Maltodextrins and hydrolysates are the terms used for glucose syrups with a dextrose equivalent (DE) of below 20 and above 80 DE, respectively. The process of hydrolysis using an acid is still a valuable tool in the manufacture of glucose syrups, although continuous systems are now routinely used. The enzyme industry has also led to advancements in glucose syrup manufacture, and various combination methods are used to create custom syrups for specific purposes.
Protein removal
Starch granules have protein in their structure, and the amount of protein varies depending on the source of starch. This protein content is unwanted because it causes browning reactions during the hydrolysis process and storage of glucose syrups. Some sources of starch, such as wheat starch, have particularly high protein content, which can cause processing difficulties. During the hydrolysis process, the protein is released and removed through a rotary vacuum filter charged with diatomaceous filter-aid. To aid filtration, a fine water mist is sprayed onto the filter-aid, and a knife edge is used to remove the spent filter-aid and protein to prevent blocking of the filter and reduced filtration rates. However, pentosans in wheat starch can hinder this process.
Carbon refining
Carbon treatment is an important step in cleaning up glucose syrups to remove off-flavours and colours. Bone charcoal is used to make the carbon, which can be in powdered or granular form. In the traditional process, powdered charcoal was added to the syrup and then removed using filters. Now, a continuous process with granular carbon is used, where syrup flows through large vertical columns and spent carbon is periodically replaced with fresh material. Granular carbon can be reactivated through heating, but this process is expensive and less effective compared to powdered carbon.
Ion exchange chromatography
The goal of the ion exchange process is to remove mineral ions from glucose syrup to lower the ash content from 0.35-0.5% to approximately 0.01%. This makes the syrup more stable and gives it a longer shelf life by removing colored bodies formed by Maillard reactions during syrup manufacture. The process involves two separate columns, a cation exchange and an anion exchange resin, in series. The resistivity of the glucose syrup is measured to monitor the column quality. Some users argue that higher mineral content syrups taste better and have specific uses, but manufacturers claim that lower mineral content syrups provide better stability and consistency. Finally, the syrup is evaporated to a solids content ranging from 72% to 81%.
Conclusion
Taking into account the above process manufacturing parameters and within the definition of what is termed glucose syrup as opposed to maltodextrin or hydrolysate, we can conclude that syrups manufactured from various sources by the same processes to the same DE will have comparable physical and chemical properties.