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GM bacteria key to cheaper xylitol production?

By Anthony Fletcher , 20-Sep-2006

GM bacteria that eat hemicellulose in corn fibre could be used as a new, biobased method of making xylitol, a mint-flavoured sweetener used in chewing gum.

US Agricultural Research Service (ARS) chemist Badal Saha and collaborators developed the modified bacteria - patent-pending strains of Escherichia coli - through a cooperative agreement with zuChem of Chicago, and the Biotechnology Research and Development Corporation in Peoria, Illinois.

Under the cooperative agreement, Saha is helping zuChem develop a commercial-scale process that could cut xylitol's production costs and open the door to its manufacture from corn and other homegrown crops.

Xylitol is increasingly being used as a sugar substitute because it has one-third fewer calories, imparts a cool mint flavour, helps fight cavity-causing bacteria and can pass through the human gut without involving insulin.

The ingredient has received academic backing within Europe. Last year the Scottish Intercollegiate Guidelines Network, which provides heathcare guidelines, included xylitol in recommendations encouraging consumers to look after their teeth.

The network said that consumers should use non-sugar sweeteners, in particular xylitol, in food and drink, and should be encouraged to use sugar-free chewing gum, "particularly containing xylitol, when this is acceptable."

Food companies are increasingly looking to cash in on this factor. The billion euro market for polyols is growing at just under three per cent, compared to over 8 per cent for high intensity sweeteners. But dental benefits could open up new sales growth areas for this polyol sugar replacer.

The current problem however is that xylitol production can be expensive. Commercial-scale quantities are derived primarily from birch-wood fibres that have been subjected to a combination of acids, high pressure and temperature, chemical catalysts, and a series of separation and purification steps.

But in studies at the ARS Fermentation Biotechnology Research Unit, Saha and colleagues used an approach called metabolic pathway engineering to retool the enzyme-making machinery of E. coli bacteria so that they could convert two hemicellulose sugars - xylose and arabinose - into xylitol.

At the laboratory scale, the bacteria were kept inside special biofermentors and fed a 'broth' of corn fibres or other hemicellulose sources. The xylitol they excreted was later purified from the broth as a white, crystalline powder.

Xylitol belongs to the polyol family of sugar alcohols and is a naturally-occurring 5-carbon polyol sweetener found in a host of fruits and vegetables. As sweet as sucrose, xylitol is the sweetest of all the polyols, but is said to have no after-taste and is safe for diabetics.

In Europe a handful of polyols - sorbitol, xylitol, lactitol, mannitol, maltitiol and isomalt - have been approved by the Scientific Committee for Food (SCF) for use in foodstuffs and fall under the 'additives' label.

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