Research Interests

Mari S. Chinn
Department of Biological and Agricultural Engineering NC State University
277 Weaver Labs Raleigh, North Carolina 27695-7625
(919) 515-6744 mari_chinn@ncsu.edu

Bio-Based Products

A focus of the work involves production of bio-based products, such as enzymes, biochemicals, biofuels and biopesticides, from agro-industrial residues and dedicated biomass crops through semi-solid fermentation technology, including solid substrate cultivation (SSC) and liquid cultivations using solid carbon sources. Research is also being done on the hybrid application of thermal and microbial conversion technologies for biofuel production from biomass. Successful process development can enhance the value of and provide alternative uses for underutilized renewable resources (e.g. corn stover, paper pulp sludge, grape-vine wastes, cotton stalks, residual sweet potato, wheat bran, grasses, swine waste etc.)

Solid Substrate Cultivation Technology

Solid substrate cultivation (SSC) involves the growth of microorganisms on solid substrates in the absence of free water for the production of enzymes and biochemicals. The use of various microorganisms in SSC and liquid fermentations utilizing solid carbon sources are being investigated for the production of low-cost cellulolytic, ligninolytic, and amylolytic enzymes. These enzymes are significant to the conversion of complex carbohydrates to simple sugars. The production of efficient and cost effective enzymes can contribute to the processing of feedstocks for value-added and biologically-based products.

Research in the improvement of SSC technologies involves reactor design and systems control, mathematical modeling of heat and mass transfer and examining microbial growth kinetics and energetics. Current projects: 1) investigate the use SSC as a microbial pretreatment of cotton stalks and an alternative method for feedstock production 2) examine the production of amylase enzymes by aerobic and anaerobic microorganisms on residual sweet potato meal in SSC, as well as crude enzyme saccharification ability and application.

Gasification and Fermentation Conversion Technology

Biomass gasification breaks down available plant biomass by partial combustion into gaseous products, synthesis gas. The synthesis gas (syngas) consists primarily of CO, CO2, CH4, H2, and N2 with some residual O2, NOx, C2 compounds, ash and tars. Some anaerobic bacterial strains are capable of converting synthesis gas components into liquid fuels and chemicals through fermentation. The combined process of gasification and fermentation can offer increased carbon conversion of lignocellulosic biomass, including lignin, and a biologically based production method for ethanol and other potential products, such as acetic acid, butanol and butyrate.

Research investigating this hybrid technology aims at enhancing the collective process efficiency of gasification and fermentation. This involves modifcation of extant gasifier design to improve the quality of synthesis gas produced, through instrumentation, control schemes and mathematical modeling. The focus of the fermentation aspect is on improving the stability of cells exposed to synthesis gas streams and increasing ethanol product yields. Studies are also carried out to examine use of sequential cultures of autotrophic bacteria and methanogens to generate two biofuel product streams. Metabolic modelling and econimic model development work are also objectives for this project. This programming is done in collaboration with Dr. Amy Grunden, Dr. Michael Flickinger, Dr. Steve Peretti and Dr. Kelly Zering.

Value Added Products from Industrial Sweetpotatoes

In the United States, over 1.6 billion pounds of sweetpotatoes are produced yearly and North Carolina growers produce nearly 40% of that total (UCCE, 2004; NCDA 2005). In contrast to the orange-fleshed food-type sweetpotato, high starch industrial sweetpotatoes (ISP), which are not intended for use as a food crop, have significant utility as a dedicated feedstock for the production of a number of bio-based products.Once available starch is effectively converted to functional sugars, they can then be used for products like ethanol, high heating value fuels, biochemicals, amino acids, and organic acids that can be used for polymers and resins. There is limited research available on effective sweetpotato starch conversion using biological methods (e.g. commercial enzymes), so investigation is needed to get a better understanding of the conversion process and the optimal parameters for high conversion efficiency considering differences in amylose to amylopectin ratios in the substrate. The purple-fleshed sweetpotato is of special interest due to its high levels of dry matter (~32%) and anthocyanins present in the flesh. The dry matter contains starch that can be converted into fermentable sugars. The deep color of the anthocyanin co-products make them an attractive source of natural food colorant for the food and textile industry. Sweetpotato anthocyanins also have several physiological functions including anti-oxidant activity, anti-cancer properties, and liver protection making them appealing to health conscious consumers. Objectives of this work are focused on establishing a biologically based approach to starch conversion for fermentable sugars and concurrent extraction of natural compounds from industrial sweetpotatoes. Scale up studies are also being ivestigated for sugar, ethanol and anthocyanin production and to allow for an intermediate step in scale prior to evaluation of processing at the pilot scale and eventually commercial operations.

Sugar Crop Conversion---Sweet Sorghum

Sweet sorghum is a sugar crop, similar to sugar cane and sugar beets, that may show promise as a source of sugar for ethanol fermentation. It is an annual crop in the grass family. It is noted for its high photosynthetic efficiency, adaptability to temperate regions and drought resistance . The pith or stalks can be mechanically pressed to release a sugar juice (15-22 °Brix) that can be filtered and directly fermented by yeasts. The primary advantage of sweet sorghum over starch and lignocellulsic sources is the reduced processing steps and inputs required for complete conversion, which may reveal improved economic benefits over corn feedstocks . Challenges in using sweet sorghum juice include the harvest time that is limited to 3-4 months per year and maintenance of juice stability. Project objectives aim to establish an on farm system capable of processing sweet sorghum stalks into a stable juice that can be subsequently fermented to ethanol and concentrated for use as an alternative fuel. Current projects examine improving jucie yields and quality, minimizing labor during harvest and juice extraction and enhnacing overall fermentation efficiency. This work is done in collaboration with Drs. Matt Veal and Larry Stikeleather.

Development of Biocatalysts

Another focus involves the development of biocatalysts (cells) that will convert substrates to value-added products more efficiently. Modifications to environmental controls and manipulation of gene expression through molecular methods are being examined to improve cellular functions and regulate metabolic pathways of microorganisms of biotechnological interest.

Anaerobic Thermophiles

Clostridium thermocellum, a thermophilic, anaerobic and cellulolytic bacterium, is capable of simultaneously hydrolyzing cellulosic substrates to simple sugars and producing ethanol. These characteristics make this organism attractive to research efforts in cost-effective conversion of plant biomass to fuel ethanol. In addition to ethanol, C. thermocellum produces lactate and acetate from cellobiose and glucose, which are also valued end products for some applications.

The fermentative pathways of other anaerobic thermophiles result in similar end products as well as useful enzyme systems for hydrolysis of sugar polymers.

Compound Extraction

A collaborative project between Drs. R. Sharma and M. Chinn examines the effectiveness of solvent extraction for the recovery of capsaicin and dihydrocapsaicin from different parts of habañero peppers. Capsaicin and dihydrocapsaicin have useful applications in medicinal treatments and food processing & safety. The development of efficient and economical extraction and purification methods for these alkaloids has the potential to redefine habañero peppers as value added products of North Carolina.