Starch
As early as the beginning of the 19th century, the German chemist Kirchhoff discovered that by boiling starch with acid, it could be converted into a sweet­tasting substance which mainly consisted of glucose.

Kirchhoff was looking for a replacement for cane sugar, which could not be supplied to Europe due to a blockade during the Napoleonic wars. However, Kirchhoff's product did not provide a complete solution to the shortage of sugar, partly because glucose is only about two­thirds as sweet as cane or beet sugar and partly because the yield using his technique was not very high.

Nevertheless, since then acid has been used to a great extent for the breakdown of starch into glucose. This technique does, however, have a number of drawbacks: formation of undesirable by­products, poor flexibility (the end­product can only be changed by changing the degree of hydrolysis) and finally, the necessity for equipment capable of withstanding acid used at temperatures of 140-150°C. In all these respects, enzymes are superior to acid.

The DE value (dextrose equivalent) is used as an indication of the degree of hydrolysis of a syrup. The DE value of starch is zero and that of dextrose is 100. Syrups with DE values from 35-43 are still widely produced by acid hydrolysis despite the drawbacks mentioned above. However, due to the formation of by­products, it is difficult to produce low­ and high­DE syrups of a high quality.

In the last 30 years, as new enzymes have become available, starch hydrolysis technology has been transformed. There has been a big move away from acid and today the vast majority of starch hydrolysis is performed using enzymes.

Furthermore, in the 1970s, an enzyme technique made possible the production of a syrup as sweet as sucrose - high fructose syrup. The production of this syrup has significantly boosted the growth of the starch industry in certain countries.

The starch industry is indisputably the second largest area of application for enzymes after detergent enzymes.

Enzymatic starch conversion
Depending on the enzymes used, syrups with different compositions and physical properties can be obtained from starch. The syrups are used in a wide variety of foodstuffs: soft drinks, confectionery, meats, baked products, ice cream, sauces, baby food, canned fruit, preserves, etc.

There are three basic steps in enzymatic starch conversion - liquefaction, saccharification and isomerization. In simple terms, the further a starch processor proceeds, the sweeter the syrup that can be obtained.

Liquefaction
Firstly, there is a liquefaction process. By using bacterial alpha­amylase on its own, a 'maltodextrin' is obtained which mainly contains different oligosaccharides and dextrins. Maltodextrins are only slightly sweet and they usually undergo further conversion.

Saccharification
Most starch treated with bacterial alpha­amylases is made sweeter using an amyloglucosidase, otherwise known as a glucoamylase.

This process is called saccharification and the amyloglucosidase can theoretically hydrolyze starch completely to glucose. In practice, a little maltose and isomaltose is produced too.

A pullulanase is a debranching enzyme that can also be used to aid saccharification. Fungal alpha­amylases can also be added in order to produce syrups with a higher maltose content, which have high fermentability and a relatively high sweetness. A high maltose content can also be obtained by using beta­amylase or Maltogenase,Ô possibly in combination with a pullulanase. A syrup produced by beta­amylase has virtually no dextrose while a syrup produced by Maltogenase contains no maltotriose.

Isomerization
Going one step further, a proportion of the glucose can be isomerized into fructose, which is about twice as sweet as glucose. An immobilized glucose isomerase is used and if it were not for this enzyme, it would not be possible to convert glucose into fructose with high yields and with few by­products. In the 1970s, Novo developed the glucose isomerase Sweetzyme^® - the first immobilized enzyme to be produced on an industrial scale. Immobilizing the isomerase enables it to be used continuously for several months.

The products of isomerization that have so far assumed the greatest importance contain approximately 42% fructose/54% glucose and 55% fructose/41% glucose. These are known as 'high fructose (corn) syrup', 'isosyrup', 'isoglucose' or 'starch sugar' depending on the end­use. They are as sweet as ordinary cane or beet sugar and have the same energy content. In many cases, a total replacement of sugar is possible without any noticeable change in the character of the product. In the USA, for example, high fructose syrup has more or less replaced the sugar previously used in the manufacture of beverages, dairy products, baked products and canned foods.

Syrups with a higher fructose content than 42% are obtained by a non­enzymatic treatment of the high fructose syrup. Pure fructose is about 40% sweeter than sugar.

Sugar
Starch is a natural component of sugar cane. When the cane is crushed, some of the starch is transferred into the cane juice where it remains throughout subsequent processing steps. Part of the starch is degraded by natural enzymes already present in the cane juice, but if the concentration of starch is too high, starch may be present in the crystallized sugar (raw sugar). If this is to be further processed to refined sugar, starch concentrations beyond a certain level are unacceptable because the filtration of the sugar solution will be too difficult.

In order to speed up the degradation of starch, it is general practice to add concentrated enzymes during the evaporation of the cane juice.

Due to its extreme thermal stability, Novo Nordisk's Termamyl^® may be added at an earlier stage of the multi­step evaporation than conventional enzymes. Termamyl is therefore the product preferred for starch degradation.

Another polysaccharide, dextran, is not a natural component of sugar cane, but it is sometimes formed in the sugar cane by bacterial growth. This happens in particular when the cane is stored under adverse conditions (high temperatures and high humidity). Dextran has several effects on sugar processing: clarification of the raw juice becomes less efficient, filtration becomes difficult, heating surfaces become 'gummed up', which affects heat transfer, and finally, crystallization is impeded resulting in lower sugar yields.

These problems may be overcome by adding a dextran­splitting enzyme at a suitable stage of the process. Novo Nordisk supplies a fungal enzyme called Dextranase for this application.

It should be added that dextran problems may also be encountered in the processing of sugar beets, although the cause of the dextran is different. In this case, dextran is usually a problem when the beets have been damaged by frost. The cure, however, is the same: treatment with a dextranase preparation.