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Scientists Monitor Bt Protein in Corn Ethanol

Protein from the soil bacterium Bacillus thuringiensis has earned much praise for its environmental and economic benefits as a natural pesticide. But less well known is what happens to the protein in Bt-modified corn when processed into ethanol.

To find out, Agricultural Research Service (ARS) chemical engineer Bruce Dien and colleagues designed small-scale experiments with wet- and dry-milled Bt corn hybrids that enabled them to monitor the protein during all stages of ethanol production.

According to Dien, with ARS’ National Center for Agricultural Utilization Research in Peoria, Ill., there’s been little prior research delving into Bt’s effects on ethanol even though Bt-modified corn accounts for roughly 25 percent of the U.S. crop.

Bt corn contains genes from the bacterium for making the protein as a built-in pesticide against the larvae of European corn borers. At each stage of their experiments, Dien’s team checked for the presence and amount of the Bt protein, CRY1Ab, using an antibody-based test called an Enzyme-Linked Immunosorbent Assay.

During dry milling, they found, the use of heat to liquefy corn meal quickly destroyed the protein, and there was no detectable trace of it in either the mash or resulting ethanol. In wet-milled corn, they detected Bt in whole kernels, gluten, germ oil and fiber at concentrations of 170 to 453 parts per billion. But nothing turned up in the starch or steep liquor fraction, used to produce the ethanol.

Ethanol yields from Bt corn also matched that of non-Bt hybrids. Typical industrial ethanol yields are about 2.7 gallons per bushel via dry-milling and 2.5 gallons for wet-milled corn.

More details about these studies, including new findings on the role of corn starch on ethanol yields, appear in this month’s issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.