Use bacteria to make a sweet, minty compound.

Even if you haven't heard of mannitol, chances are you've eaten this minty-tasting sugar alcohol as a powdery coating on chewing gum, candies or pills. It's also used as a low-calorie sweetener, a diuretic and as an agent that adds body to foods.

Mannitol is produced naturally by certain plants, though not to a degree that satisfies our many uses for it. Now, rather than chemically manufacturing mannitol, USDA-ARS scientists are using a Lactobacillus bacterium steeped in high-fructose syrup to do the job inside fermentation flasks.

The researchers developed the bio-based approach as a more efficient alternative to industrial processes now used. Their goal is to replace the chemical processes with bio-based methods. They can use just about any kind of carbohydrate material containing fructose and convert it to mannitol using this technique.

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, HPH converts only about 30% of these sugars into mannitol, which sells for $3.32 per pound. The rest is mostly sorbitol, a lower-priced sugar alcohol at $0.73 per pound.

The new bio-based method converts up to 72% of fructose into mannitol. Central to this approach is L. intermedius NRRL B-3693, a strain the scientists chose from 72 other bacteria specimens in the ARS Culture Collection. The researchers grow the Lactobacillus strain inside a fermentation flask containing a broth of fructose, glucose or other carbohydrates. Later, they refrigerate the broth and remove the bacteria's "leftovers"--white, needle-like crystals of mannitol.

In trial runs the scientists observed that, on average, the Lactobacillus strain will convert 250 grams of corn fructose to 175 grams of mannitol. 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 2 to 1 (100 grams to 50 grams), the researchers obtain almost 100% conversion of fructose to mannitol. With a sucrose-fructose mixture of 2 to 1, they find a conversion yield of 85% mannitol from fructose.

The scientists also compared the Lactobacillus strain's performance with 11 other bacteria, yeast and fungi. One top-performing rival--Lactobacillus sp. Y-107--was given 100 grams of fructose and took 120 hours to convert about 73% of it into mannitol. The Lactobacillus strain, given 150 grams of fructose, converted about the same amount--72%--in just 15 hours. Such speed may bolster commercial prospects. The USDA has applied for a patent on the strain along with methods of using it, and a company is evaluating the technology.

Further information. Badal Saha, USDA-ARS National Center for Agricultural Utilization Research, 1815 N. University St., Peoria, IL 61604; phone: [phone]; fax: [phone]; email: [e-mail].