Dextran, a microbial fermentative hydrocolloid, is a linear polysaccharide made of many glucose molecules joined as chains of varying length. It was the first industrial polysaccharide produced by lactic acid bacteria (LAB) and is also one of the first water soluble gums known to man. Additionally, dextran is one of the first microbial polysaccharides to be commercialised and to be approved for use in food.
The Dextran polysaccharide chain is lengthened using the enzyme dextran sucrose, which sequentially adds glucose units to the molecule chain. The biosynthesis of dextran has been demonstrated in numerous bacteria, especially in Streptococcus mutans, Leuconostoc mesenteroides ssp. mesenteroides and Leuconostoc mesenteroides ssp. dextranicum. Leuconostoc produces the enzyme dextran sucrase and secretes it into the culture medium in the presence of sucrose. This enzyme, dextran sucrase, then synthesises dextran from the sucrose substrate. Dextran is an extremely versatile compound and it wide potential uses are favoured by the different properties of the polymer such as; (i) neutral and water soluble, (ii) stable for more than 5 yr., (iii) biocompatibile: Dextran can be safely consumed and (iv) is biodegradable.
Dextran has applications in several fields. It is used especially in biochemistry as a support for filtration chromatography on a Sephadex type gel. Furthermore, dextran is applied in the food industry to increase the texture of food products such as yoghurts, cream desserts, milk-based drinks and salad dressings
A fragment of the dextran structure is shown in figure 1.