The Dextran Story

The dextran molecule rotates polarised light three times as much as sucrose and therefore its presence in the cane juice, even in minute amounts, leads to false polarimetric (pol) readings. A farmer delivering dextran-contaminated cane could, since the cane is valued on the basis of the pol measurement, receive higher payment than a farmer who has produced good cane. In addition to this, the bad cane will continue to cause problems with further financial losses in the factory, refinery and during the trade of the product at all stages.

The bacteria capable of producing dextran from sucrose are mainly Leuconostoc species and are ubiquitous in the soil. They enter the cane at sites of exposed tissue caused by machine harvesting, cutting, burning, freezing and via disease and pests. Wet muddy cane is the most at risk.

Any delay in the "kill to mill" time will allow the bacteria to proliferate and the dextran levels will soar as a result.

The name dextran represents a group of related polymers whose structures and properties can vary widely depending on the source organism and environmental factors such as sucrose concentration, pH, temperature and aeration (Imrie and Tilbury, 1972).


This family of molecules are formed from chains of glucose units, varying greatly in size and the degree of branching. They are usually soluble in water but insoluble in alcohol. The latter trait is often exploited for the purpose of crude detection tests. The presence of dextran in the juice acts firstly to increase the viscosity. This leads to "gumming" of the factory machinery and formation of a slimy layer that blocks filter cloths.

The viscosity also leads to reduced heat transfer and slowing of evaporation rates.

The effect dextran has on the crystallisation process can be dramatic by preventing the extension of lateral faces, leading to needle shaped crystals (Muller, 1981).

The insolubility of dextran in alcohol means that sugars and syrups containing it are unsuitable for the production of alcoholic beverages.

The conventional remedy to any problem caused by dextran in process is the addition of the enzyme dextranase, which will hydrolyse the large dextran molecules into smaller oligosaccharide products. This is an expensive treatment largely because of the cost of the enzyme.

Without accurate knowledge of the quantities of dextran present in the process, it is impossible to gauge the correct amount of dextranase required.

Dextran detection is, and long has been, dominated by two equally questionable techniques, namely the haze and the Roberts (Keniry et al., 1969 and Roberts, 1983 respectively) tests. Both tests exploit the dextran's tendency to precipitate out of solution in alcohol. These current industry standards for dextran quantification, have long been proved unreliable and inaccurate as well as non-specific, costly and time consuming (Kubik et al., 1994, DeStefano and Irey, 1986, Curtin and McCowage, 1986, and Brown and Inkerman, 1992).

Many alternative tests have been proposed and investigated, often as modifications on the theme of alcohol precipitation with various chemical and/or enzymatic inclusions. Although these tests are often arguably more reproducible and accurate, they are generally expensive and labour intensive to perform; hence, they are unattractive to the majority of sugar technologists.

There is a long-standing need for a fast, accurate, simple and inexpensive method for the detection and quantification of dextran.

The Optical Activity DASA System is it ...

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DeStefano, R. P. and Irey, M. S. (1986). Measuring dextran in raw sugars – historical perspective and state of the art. J. American Society Sugar Cane Technologists, 6, 112-120.
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