Using Bacteria To Make a Sweet, Minty-Tasting 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
an agent to add body to foods.
Mannitol is produced naturally by certain plants, though not to a degree
that satisfies humankind's myriad uses for it. Now, rather than chemically
manufacturing mannitol, a Peoria, Illinois, scientist is using a Lactobacillus
bacterium steeped in high-fructose syrup to do the job inside fermentation
Agricultural Research Service
chemist Badal Saha developed the biobased approach as a more efficient
alternative to industrial methods now used. "Our goal is to replace
these chemical processes with biobased methods," says Saha, at
ARS' National Center for Agricultural Utilization Research, in Peoria.
"We can use just about any kind of carbohydrate material containing
fructose and convert it to mannitol by this method," he adds.
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, says Saha, HPH
converts only 25-30 percent of these sugars into mannitol, which sells
for $3.32 a pound. The rest is mostly sorbitol, a lower-priced sugar
alcohol (73 cents a pound).
In a paper accepted for publication in Biotechnology and Bioengineering,
Saha reports that his biobased method converts up to 72 percent of fructose
Central to this approach is L. intermedius NRRL B-3693, a strain
the scientist chose from 72 other bacteria specimens in ARS' Culture
Collection, also in Peoria.
Nature endowed this strain with 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 grows the Lactobacillus strain inside a fermentation
flask containing a broth of fructose, glucose, or other carbohydrates.
Later, he refrigerates the broth and removes the bacteria's "leftovers"white,
needle-like crystals of mannitol.
In trial runs, he observed that on average, the Lactobacillus
strain will convert 250 grams of corn fructose to 175 grams of mannitol.
Saha says fructose is the strain's main carbon source. But up to two
thirds of it can be replaced by other sugars, including maltose and
"With a fructose/glucose mixture of 2 to 1 (100 grams to 50 grams),
we get almost 100 percent conversion of fructose to mannitol,"
says Saha. "With a sucrose/fructose mixture of 2 to 1, we get a
conversion yield of 85 percent mannitol from fructose."
Saha also compared the Lactobacillus strain's performance with
11 other bacteria, yeast, and fungi. One top-performing rival given
100 grams of fructose took 120 hours to convert about 73 percent of
it into mannitol. The Lactobacillus strain, given 150 grams of
fructose, converted about the same amount (72 percent) in just 15 hours.
Such speed may bolster its commercial prospects: USDA has patented
the strain along with Saha's methods of using it, and a company is now
collaborating with him to further evaluate the technology.By Jan
Suszkiw, Agricultural Research Service Information Staff.
This research is part of Quality and Utilization of Agricultural
Products, an ARS National Program (#306) described on the World Wide
Web at www.nps.ars.usda.gov.
Badal C. Saha is with the USDA-ARS National Center for Agricultural Utilization Research, 1815 N. University St., Peoria, IL 61604; phone (309) 681-6276, fax (309) 681-6427.
"Using Bacteria To Make a Sweet, Minty-Tasting Compound" was published in the March 2003 issue of Agricultural Research magazine.