fforts in the College of Agriculture and Life Sciences to develop value-added products through bioprocessing will be complemented by the work of two of the College’s newest faculty members: Dr. Mari Chinn and Dr. Ratna Sharma.

Both Chinn and Sharma are members of the Department of Biological and Agricultural Engineering. Sharma joined the faculty in May 2003, while Chinn arrived three months later in August.

Sharma anticipates that much of her work will focus on producing biofuels such as ethanol as well as other biologically based products from North Carolina crops or crop residues. She’s already working with cotton stalks (the residue of a cotton harvest; see related article- Profit from (Bio)Process) and plans to work with sweetpotatoes.

Of course, making alcohol from various crops is nothing new. Indeed, North Carolina and many parts of the South have a rich – some would say infamous – history of turning organic matter into “biofuel.” The crops of choice were usually corn, wheat or barley, and the result was an alcoholic beverage. Those who produced such “fuel” were often called bootleggers.

It is not difficult to produce fuel ethanol from biomass. The difficulty, Sharma points out, arises in producing a fuel that is economically competitive with petroleum-based fuels.

Sharma explains that ethanol results from the fermentation of sugars obtained from converted organic matter. But before fermentation can begin, the starch in sweetpotatoes and the cellulose in cotton stalks must be converted to simple sugars, and therein lies much of the cost of producing biofuels. Sharma plans to spend much of her time working on more efficient methods of degrading lignocellulosic plant material into sugars, thus making biofuel production more economically competitive.

Sharma may also experiment with supercritical carbon dioxide extraction technology. Carbon dioxide, Sharma explains, has unusual properties at certain temperatures and pressures and can be used to extract products such as alkaloids from plants or, perhaps, pigments from sweetpotatoes (see previous article). The trick is to find just the right temperature and pressure for the substance you want to extract.

Chinn is also interested in converting plant biomass into value-added products, but she plans to take a different approach. Chinn plans to focus on solid substrate cultivation of microorganisms as opposed to liquid cultivation as a means of biological conversion.

Solid substrate cultivation, Chinn explains, is an alternative to liquid cultivation for the production of value-added biologically based products such as enzymes, biochemicals or antibiotics. Liquid cultivation involves the growth of microorganisms in a liquid medium containing a carbon source and other nutrients. The microorganisms feed on the carbon source and in so doing convert it to the product of interest.

Solid substrate cultivation involves cultivation of microorganisms on solid material, or substrate, rather than in a liquid. The solid substrate can be an agricultural product, such as wheat bran, corn stover (the residue of a corn harvest) or sweetpotatoes. The agricultural product serves as the carbon and nutrient source for microbial growth and product generation.

Solid substrate cultivation has the potential to be more cost effective than liquid cultivation for some applications, Chinn says. Liquid culture usually requires more involved medium preparation — the raw material being processed must be liquified — as well as higher working volumes and expensive product separations.

The simplified processing conditions for solid substrate cultivation could reduce production and separation costs, says Chinn, “and typically we see higher product concentrations in solid substrate cultivation.”

Chinn says it may be possible to produce biological control agents for pest management using solid substrate culture. The solid substrate cultivation product (the biological control organism) could potentially be applied directly, without any further processing.

And of course solid substrate culture may be used to convert biomass to sugars. And the sugars can then be converted to a range of products, everything from pharmaceuticals to biofuels and bioplastics.

“ Economical production of simple sugars from complex carbohydrates (e.g. lignocellulosic and cellulosic substrates) for such applications can be challenging,” says Chinn. If Chinn can develop solid substrate cultivation methods to produce cost effective enzymes used in the conversion of plant biomass into simple sugars, then more value-added products may be derived from renewable resources.

She adds that enzymes produced using solid substrate cultivation might also be used as animal feed supplements. Solid substrates with which Chinn anticipates working are paper pulp sludge, wheat bran, corn stover, sweetpotatoes, and maybe even the solid portion of swine manure.