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Dissertation - University Access Only
Doctor of Philosophy (PhD)
Chemistry and Biochemistry
Extraction is indispensable for chemical processing and plays a crucial role for both qualitative and quantitative analysis. Conventional extraction techniques employ the use of organic solvents which are known to be toxic, flammable, expensive, and have negative environmental impact. The use of alternate solvents that are safe, renewable, and produce high quality extracts can be used to address these shortcomings. Supercritical carbon dioxide (SCO2) is generally regarded as safe (GRAS) and it has mild critical point values (73 atm, 31 °C) which are easily achievable. It is relatively inert, making it ideal for chemically and thermally labile compounds. It possesses dual characteristics, i.e. it dissolves like a liquid and diffuses like a gas, which is easily fine-tuned by changing temperature and pressure values. Besides, carbon dioxide is ubiquitous, cheap, recyclable, and it leaves no residue on the extract. Supercritical fluid extraction (SFE) using carbon dioxide as an alternate solvent was explored in processing of selected agricultural products (beeswax, distillers dried grains with solubles, and waste sheep wool) to produce value-added products. Beeswax is composed of esters of fatty acids and long-chain aliphatic alcohols with major application in pharmaceutical and cosmetic industries. Conventional extraction methods employ the use of organic solvents such as heptanes and hexanes. SCO2utilization was explored in beeswax refinement from honeycomb, slumgum, filter cake, and cappings. Vital parameters on extraction efficiency, pressure, temperature, and time, were investigated. Optimum extraction conditions for a 1.0000 g sample were found to be 10,000 psi, 70 °C, and dynamic extraction time of 30 min, with a 1:1 ratio of wax to activated carbon for complete bleaching. The flow was maintained at 0.5-1.0 mL/min of the condensed gas. Fatty acids, alcohols, and aliphatic hydrocarbons with carbon-chain lengths of C16-C30, C24-C30, and C23-C31 respectively were identified using GC-MS. This was in agreement when compared with the standard wax and, therefore, simultaneous extraction and bleaching of beeswax wax using carbon dioxide maintained its quality and SCO2 can serve as an ideal alternate solvent. Fourier-transform infrared spectroscopy (FTIR) showed similar absorbance bands when compared to commercial beeswax, while differential scanning calorimetry (DSC) confirmed the melting point to be approximately 62 °C which falls within the literature range (62-65 °C). Distillers dried grain with solubles (DDGS) is a byproduct during the ethanol production process from corn that is exclusively used as a livestock feed. It contains low starch and high levels of protein, fiber, minerals, and vitamins, making it ideal as a diet to treat medical conditions like diabetes and celiac disease in human beings. The presence of fatty acids creates an off flavor, while the dark color affects the appearance of baked products limiting its utilization. Bleaching of corn distillers dried grain with solubles (DDGS) to produce an upgraded food ingredient using SCO2as an alternate to ethanol washing was investigated. With a sample size of 5.0000 g, pressure, temperature and time of 5,000 psi, 50 °C, and 20 min respectively were found to be optimal at a flow of 1.5-2.0 mL/min of the condensed gas. Using a Hunter colorimeter, the residual DDGS color values of L*, a*, and b* were 81.47 ± 0.28, 1.05 ± 0.05, and 22.83 ± 0.61 respectively while palmitic acid, stearic acid, oleic acid, and linoleic acid were the major fatty acids present in the extract. Crude protein content of the processed DDGS was found to be 33.50 ± 0.20% w/w which was in agreement with the DDGS obtained via the ethanolwashing method. Waste sheep wool possesses no economic value and requires laborious and costly methods for its refinement. However, it contains lanolin, a high-value product in the cosmetic and pharmaceutical industries because of its emollient features. Supercritical carbon dioxide was employed to selectively isolate lanolin without any prior clean-up process. Response-surface methodology was applied to optimize the processing parameters using face-centered central-composite design. The independent variables were pressure (5,000-10,000 psi), temperature (60-100 °C), and time (20-80 min). Optimized conditions that gave the highest recovery were identified as 10,000 psi pressure, 100 °C temperature, and 66 min dynamic extraction time. The sample size was approximately 1.0000 g and the flow was maintained at 1.5-2.0 mL/min of the condensed gas. Using these optimized conditions, wool grease was extracted and refined from tags, greasy fleece, and choice fine wool. Comparative characterization using GC-MS was conducted for qualitative analysis. Branched fatty acids (iso or anteiso) ranging from C13-C30, alcohols ranging from C16-C30, and sterols formed the major composition of the extracted lanolin. DSC thermograms showed similar behavior between our refined lanolin and commercial lanolin. Overall, the results compared well with commercial lanolin and florisil at a ratio of 1:1 with wool grease showed the best results for bleaching and deodorization.
Library of Congress Subject Headings
Supercritical fluid extraction
Includes bibliographical references (pages 109-120)
Number of Pages
South Dakota State University
In Copyright - Educational Use Permitted
Gachumi, George, "Application of Supercritical Carbon Dioxide in Agricultural Products Processing" (2015). Electronic Theses and Dissertations. 1660.