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Chemical description

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.



Did you know?

In the 1940s, Allene Jeanes was a scientist at the USA's Northern Regional Research Laboratory.

A soft drink company had sent her a sample of their product, which had mysteriously become thick and gooey. She soon found that a bacterium had converted the sugar in the soda to dextran. Perhaps the bacteria had come from some worker's dental plaque! She found that the bacterium could be grown in the lab in a vat of sugar solution, and make lots of dextran. During World War II, doctors tried transfusing plasma which is blood without any cells in it. It does not cause complications, and can immediately increase the blood pressure and replenish electrolytes. However, plasma can spoil easily, so it must be kept on ice all the time. In the battlefield, where do you store plasma? That's where dextran helps. It can be carried dry, quickly mixed with water and salt and transfused to the patient. It pushes up the blood pressure immediately, while the saline helps restores some electrolytes. Dextran was then purified, dried, and sent to Korea. There it would help soldiers survive the journey from battlefield to hospital, where they could be treated further.

Food Applications

Introduction to dextran as food ingredient.

Dextran was initially studied in the 1950s as food ingredient, particularly as a thickener. The US Food and Drug Administration currently lists dextran as GRAS (Generally regarded as safe) as ingredient for food and feed applications. In 2001, the European Commission approved the use of dextran in baked goods, up to levels of 5%

Bakery Products

 

The incorporation of dextran into bakery products improves softness, crumb texture and loaf volume. The addition of 2% native dextran increases the water absorption of flour dough by about 12%.


Confectionery

 

Dextrans have also been used as additives in products such as candy and ice creams. It has been used as a stabiliser for confectionery where its presence prevents crystallisation, improves moisture retention, increases viscosity and maintains flavour attributes. Its use is also proposed in soft drinks, flavour extract, milk beverages and icing.


Ice cream

 

As an edible substance, dextrans are bland odourless, tasteless and nontoxic. They are considered to have many advantages over other ice cream stabilisers. Tests performed on ice cream mixes containing 2-4% dextran indicated that it conferred beneficial properties on the product viscosity.


Cheese-making: reduced-fat cheese

 

Fat reduction is associated with many textural and functional defects in cheese. The high casein content in reduced-fat cheese imparts a firm and rubbery body and texture. EPS, in particular, Dextran, is a good candidate for reduced-fat cheese making for several reasons. It has the ability to bind water and increase the moisture in the non-fat substance with no need to modify the cheese-making protocol. This is an important function because fat reduction results in lower moisture in non-fat products.


Frozen and Dried foods

 

The favourable properties of dextran for stabilising vacuum packed, air dried, and freeze-dried or frozen foods enable its use in fish products, meat, vegetables and cheese surfaces. A film of dextran could protect food from oxidation and other chemical changes also helping to preserve texture and flavour. The increasing demand for fast food and table ready dishes in a frozen or dried state creates an opportunity for the use of dextran as a food preservative, as well as a texture, flavour and scent enhancer.


Waste water management

 

Dextran finds a wide range of application in waste water management. Many industries are searching for environmentally acceptable products for treating waste water effluent. Dextran offers many useful features like the stabilisation of alkali and acids at room temperature. It binds metal ions at an alkaline pH and is biodegradable and economical. It is used extensively in waste water treatment during the flocculation process.

Last news

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