The food industry could shortly be using a new, bio-based approach to manufacturing mannitol - the minty-tasting sugar alcohol used as a powdery coating on chewing gum, confectionery and pills - as scientists report on new method to replace the traditional chemical manufacturing method.
Researchers at the Agricultural Research Service (ARS) of the US Department of Agriculture have developed a method that uses Lactobacillus bacterium steeped in high-fructose syrup inside fermentation flasks to produce mannitol. They claim that their biobased approach is a more efficient alternative to industrial methods currently used.
"Our goal is to replace these chemical processes with biobased methods," said leading researcher Badal Saha, at ARS' National Center for Agricultural Utilisation Research, in Peoria. "We can use just about any kind of carbohydrate material containing fructose and convert it to mannitol by this method," he added.
Manufacturers currently produce mannitol by subjecting a 50-50 mixture of fructose and glucose to a nickel catalyst and high-pressure hydrogenation (HPH). But in addition to generating chemical wastes, claims Saha, HPH converts only 25-30 per cent of these sugars into mannitol. The rest is mostly sorbitol, a lower-priced sugar alcohol. Saha reports that his biobased method - since patented by the USDA - converts up to 72 per cent of fructose into mannitol.
Central to this approach is L. intermedius NRRL B-3693, a strain that possesses a powerful metabolic enzyme that enables it to free up the sugars' carbon as food. Mannitol, lactic acid and acetic acid are the byproducts of this action.
In the lab, Saha grew the Lactobacillus strain inside a fermentation flask containing a broth of fructose, glucose or other carbohydrates. Later, he refrigerated the broth and removed the bacteria's 'leftovers' - white, needle-like crystals of mannitol.
In trial runs, Saha reports that on average, the Lactobacillus strain will convert 250 grams of corn fructose to 175 grams of mannitol. Saha maintains fructose is the strain's main carbon source. But up to two thirds of it can be replaced by other sugars, including maltose and sucrose.
"With a fructose/glucose mixture of two to one (100 grams to 50 grams), we get almost 100 per cent conversion of fructose to mannitol," said Saha. "With a sucrose/fructose mixture of two to one, we get a conversion yield of 85 per cent mannitol from fructose."
Saha also compared the Lactobacillus strain's performance with 11 other bacteria, yeast and fungi. One top-performing rival, reports Saha, given 100 grams of fructose took 120 hours to convert about 73 per cent of it into mannitol. The Lactobacillus strain, given 150 grams of fructose, converted about the same amount (72 per cent) in just 15 hours.
Full findings will be published in Biotechnology and Bioengineering.