Chemist Badal Saha
(left), technician Greg Kennedy (center) and student aide Ohiole Ake stand next
to a biofermentor where sugar alcohols including xylitol are produced by
bacteria or yeasts. Click the image for more information about
High-Tech Microbes Could Bolster Production of
Natural Sweetener By
Jan Suszkiw September 18, 2006
Genetically engineered bacteria that eat hemicellulose in corn fiber
and other sources could set the stage for a new, biobased method of making
xylitol, a mint-flavored sweetener used in chewing gum, toothpaste, mouthwash
and other products.
Agricultural Research Service (ARS) chemist
Saha and collaborators developed the modified bacteriapatent-pending
strains of Escherichia colithrough a cooperative agreement with
zuChem, Inc., of Chicago, and the
Biotechnology Research and Development
Corporation in Peoria, Ill.
Xylitol is produced naturally by many fruits and vegetables, and even
to some degree by the human body. It is used as a sugar substitute because it
has one-third fewer calories, imparts a cool mint flavor, helps fight
cavity-causing bacteria, and can pass through the human gut without involving
Commercial-scale quantities are derived primarily from birch-wood
fibers that have been subjected to a combination of acids, high pressure and
temperature, chemical catalysts, and a series of separation and purification
steps. But the process is expensive, and the resulting xylitol must be
imported, primarily from Finland and China, notes Saha, who works at the ARS
Center for Agricultural Utilization Research in Peoria.
In studies at the center's
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
sugarsxylose and arabinoseinto xylitol. At the laboratory scale,
the bacteria were kept inside special biofermentors and fed a "broth" of corn
fibers or other hemicellulose sources. The xylitol they excreted was later
purified from the broth as a white, crystalline powder.
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 in the Unites States from corn and other homegrown
ARS is the U.S. Department of
Agriculture's chief scientific research agency.