See related story- New Faculty Members Focus on Bioprocessing
But farmers in the future may look at these and other crops a bit differently if researchers in the College of Agriculture and Life Sciences are successful in efforts to increase the value of crops through bioprocessing.
“ We need to add value to our agricultural commodities,” says Dr. Mike Boyette, Philip Morris professor of biological and agricultural engineering. Bioprocessing appears to hold promise as one method of adding that value. And cotton, sweetpotatoes and tobacco appear to be among the crops most suited to bioprocessing.
Removing cotton from a cotton plant was once a backbreaking physical activity. Now, of course, it’s done by machine, which is more efficient. But it’s still not perfect. Cotton pickers do not pick all the cotton in a field.
A recently harvested cotton field looks, in Boyette’s words, “like somebody needs to harvest again.” Cotton bolls that the picker missed typically litter the field, while the stalks of the plants on which the bolls grew remain in the field, and immature cotton bolls that have not yet opened cling to the stalks.
Since the fall of 2002, when Lenoir County farmer Kendall Hill delivered a load of cotton field residue to Weaver Labs, where Boyette’s office is located, Boyette has been working to find a value-added use for what he calls cotton stalks. Hill suggested compressing the residue so that it might be turned into fire logs. Boyette tried that, but it didn’t work. Without a binder, the material wouldn’t remain compressed, and adding a binder made the process too costly.
Boyette is a resourceful researcher who tends to think not only outside the box, but outside his department, which is where he began looking for things to do with cotton residue.
The cotton in the residue has long fibers, and Boyette thought that because of that characteristic it might be possible to make paper from the material. He contacted Dr. Hou-min Chang in N.C. State’s Department of Wood and Paper Science, who agreed to experiment with the material. Chang was able to make a heavy paper out of the material, and may continue to work with the residue as more material becomes available this year.
At the same time, Boyette contacted Dr. Behnam Pourdeyhimi, director of the Nonwoven Cooperative Research Center in the College of Textiles, to see if Pourdeyhimi might have any ideas. Pourdeyhimi began working with the material and was able to make mats that Boyette thinks could be used on construction sites to control erosion.
Making such mats, which are required at many construction sites, is a $100 million a year industry, Boyette says, and most of the mats now used are made from aspen or coconut. Boyette thinks cotton residue mats could well be competitive with those now used. And with roughly a million acres of cotton, North Carolina should be able to supply plenty of material.
It should also be possible to process the residue, then ferment it to produce ethanol, and Dr. Ratna Sharma, assistant professor of biological and agricultural engineering, is working on this (see related story-- New Faculty Members Focus on Bioprocessing).
Dr. Craig Yencho, associate professor of horticultural science, calls the sweetpotato a “starch factory par excellence.” That’s one reason Yencho and others see unrealized potential in sweetpotatoes.
Indeed, Yencho is working with Ken Pecota, horticultural science researcher, and Dr. Bryon Sosinski, research assistant professor of horticultural science and director of the Genome Research Laboratory, on several fronts to add value to sweetpotatoes.
In addition to starch content, Yencho says sweetpotatoes “are capable of producing tremendous amounts of biomass in a short period with relatively few chemical inputs.” Large amounts of biomass and starch are key elements in one of the more intriguing projects on which Yencho, Pecota and Sosinski are working.
Sweetpotatoes can be processed to produce a variety of products ranging from ethanol to high-fructose syrup to pharmaceuticals. To make ethanol, for example, sweetpotatoes must first be processed to turn the starch in the potatoes into sugars. Then the sugars can be fermented to make ethanol. The same kind of two-step process applies to other products.
Yencho, Pecota and Sosinski think they can get around one of those steps. Sosinski is working with Dr. Robert Kelly, Alcoa Professor of Chemical Engineering, to insert into sweetpotatoes genes from hypothermophilic bacteria. The genes produce enzymes with what Sosinski calls “unique capabilities.” At high temperatures, the enzymes degrade starch, turning it into sugars.
The researchers hope that sweetpotatoes containing the enzymes will, in effect, self process. Under normal, lower temperature conditions during the growing season, the enzymes will be inactive. But raise the temperature and the enzymes activate, turning the starch in the potato into sugars.
“ We’ve got a couple of enzymes that are really, really efficient” at degrading starch, says Sosinski.
Enzymes and the processing involved in turning starch to sugars represent one of the major costs of making ethanol and other products from crops such as corn and sweetpotatoes, so inserting starch-degrading enzymes into sweetpotatoes could improve the economic feasibility of processing potatoes dramatically.
Yencho points out that sweetpotatoes are harvested by hand, a significant
be sorted by
shape. Hand harvesting
probably wouldn’t be necessary for what Yencho calls industrial-type sweetpotatoes.
Size and shape wouldn’t matter.
But producing the proteins in plants may be cost effective. Sosinski points out that if a protein were expressed throughout a sweetpotato plant – in the leaves as well as in the storage root – then it might be possible to mow the leaves several times during the growing season and extract proteins, then dig the roots and again extract proteins.
Then there are purple sweetpotatoes.
Plant breeders Yencho and Pecota are working to develop purple-flesh sweetpotatoes adapted to North Carolina growing conditions. The purple pigment in the potatoes is extracted to make food coloring and dye.
Yencho anticipates a “$20 to $40 million market [for purple sweetpotatoes grown in North Carolina] right off the bat.” If a well-adapted purple-flesh sweetpotato can be developed, the researchers think 5,000-10,000 acres might eventually be devoted to the crop.
“ The potential is very substantial,” says Pecota.
At the same time Yencho and Pecota are using conventional plant breeding techniques to develop purple-flesh potatoes adapted to North Carolina conditions, Sosinski is looking at using genomic techniques to turn on dormant purple-flesh genes in industrial-type sweetpotato varieties that are already adapted to North Carolina conditions.
“ We’re blending basic and applied science to solve real-world problems,” says Yencho.
Tobacco would seem another likely candidate for bioprocessing, although one of the processes will be genetic manipulation.
Tobacco tends to be a particularly malleable plant when it comes to genetic manipulation. It’s relatively easy to insert genes into tobacco, so it should be possible to genetically engineer tobacco to contain valuable products, such a proteins, then grow the crop for these products.
Yet while natural systems may sometimes appear to be fairly simple, they tend to be complex, and manipulating them can be easier said than done. Just ask Dr. Arthur Weissinger, professor of crop science.
Weissinger has been working for the last five years to insert into tobacco a gene from the canine papilloma virus that produces a protein. The protein can be used to make a vaccine that conveys protection from the virus, which causes warts in the mouths of dogs.
Weissinger is using the canine papilloma virus as a model. He hopes eventually to engineer tobacco to produce a protein that may be used to make a vaccine for the human papilloma virus. The human virus causes cervical lesions in women, which can lead to cervical cancer.
In the developed world, pap smears catch most cases of cervical cancer when the disease can be treated. But Weissinger points out that’s not the case in the undeveloped world, where an inexpensive vaccine could save many lives.
Weissinger’s is a bit of a cautionary tale for those who wish to manipulate natural systems. He thought it would be relatively easy to make the viral gene work in tobacco. It turns out the protein is fragile and tends to degrade in the plant that is making it before it can be purified to make the vaccine.
“ We’ve taken the gene and modified it a lot of different ways so it is more easily expressed in plant cells and is potentially more recoverable,” says Weissinger. He is now working to determine which of a number of different genetic constructions work the best.
“ We’re in the optimization phase,” he adds. “We do have plants that are making the protein.”
But that’s hardly the end of the project. Now methods of removing the protein from the plant must be developed. The protein will then be used to make viruslike particles that will be used as a vaccine. Then the vaccine must be tested on dogs.
“ We know from the physicians we work with that the vaccine for people works the same way [as a vaccine for dogs],” Weissinger says. By working with the dog model, researchers are gaining valuable experience that will help them when they begin to produce vaccines against human papilloma virus.
Complementing Weissinger’s work is that of Dr. Jennifer Levin, assistant professor of crop science and a tobacco breeder. Levin is working to develop tobacco varieties suited to the production of value-added products.
Levin began by looking through the College’s tobacco germplasm collection of more than 1,000 kinds of tobacco for a type with more leaf protein than others. She found what she calls “a primitive-type tobacco line.” She’s now crossing this primitive line with varieties with high yield and disease resistance in an effort to produce a variety that may be suitable for protein production.
Levin is also looking at how production practices that might be used to grow tobacco for proteins or other substances may affect the variety being grown. This year she grew her crosses in rows 7 inches apart as opposed to the typical 21 inches.
She points out that disease resistance may be particularly important if tobacco is grown in such dense plantings. The leaves will tend to remain moist longer, which may make the plants more susceptible to diseases like blue mold or tobacco mosaic virus.