Design of Processing Conditions for Conversion of Sugar and Starch Based Crops to Value Added Products.

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Title: Design of Processing Conditions for Conversion of Sugar and Starch Based Crops to Value Added Products.
Author: Bridgers, Elizabeth Nicole
Advisors: Mari S. Chinn, Committee Chair
V. Den Truong, Committee Member
Matthew W. Veal, Committee Member
G. Craig Yencho, Committee Member
Abstract: This study focused on sweet sorghum and purple-fleshed industrial sweetpotatoes. Sweet sorghum is a crop which produces relatively high quantities of easy to process, directly fermentable aqueous sugar. Purple-fleshed industrial sweetpotatoes (ISPs) offer two viable resources for value added products in its combination of high dry matter (~32%) and anthocyanin content. The objectives of this project was to generate the information necessary to investigate the processing conditions for maximum ethanol production of sweet sorghum juice preparations, examine the effectiveness of different enzyme treatments on glucose and ethanol production as well as procedures for anthocyanin extraction from purple-fleshed industrial sweetpotatoes, and create a demonstration scale system for processing sweet sorghum and ISPs so that scale up processing conditions and related challenges can be studied. The effects of pH level, yeast type, incubation time and sterilization were investigated on sorghum juice preparations. Ethanol and individual sugar concentrations (sucrose, fructose and glucose) were measured over time. Sterile treatments typically resulted in >84% conversion of sugars to ethanol, while nonsterile treatments ranged between 60-75% conversion. Yeast type did not impact ethanol fermentation. Sterilization may not be necessary and generally will not support the most cost-effective process, while lowering pH and freezing could potentially preserve nonsterile fresh juice. The effects of different ISP preparations, enzyme loadings, and time on starch conversion and sugar production during liquefaction and saccharification were examined, in addition the effects of yeast concentration and salt supplementation on fermentation of produced sugars to ethanol were investigated. Results showed that the majority of available starch, 44.2 and 49.6% of dry matter, was converted during liquefaction of flour and fresh sweetpotato preparations, respectively, with the addition of 0.045 KNU-S/g dry ISP of Liquozyme SC after 2 hours incubation (68.8 and 67.0% initial starch contents, respectively). Saccharification was able to increase the breakdown of starch, but its primary function was conversion of short chain carbohydrate polymers to fermentable sugars. The addition of 5.0 AGU/g of Spirizyme Ultra was able to produce 644 and 582 mg/g starch in flour and fresh preparations, respectively. Yeast were able to produce 39.2 and 48.8 g/L of ethanol for flour (25% w/v substrate loading) and fresh (12.5% w/v) ISP, respectively, after 48 hours using 0.1% w/v yeast without salts. The effects of solvent type, solid loading, and incubation temperature on total monomeric anthocyanin and phenolic concentrations during extraction processing of purple-fleshed sweetpotatoes were determined. A subsequent hydrolysis process evaluated the effect of initial extraction conditions on the production of fermentable sugars. A maximum anthocyanin yield of 186.1 mg cyd-3-glu/100g fw was extracted from purple-fleshed ISPs. Greater recovery of anthocyanins was achieved at the higher extraction temperature of 80°C using acidified solvents. The sugars generated during hydrolysis of residual solids from extraction were not as easily fermentable as sugars derived from ISPs that had not undergone extraction. Residual solvent from the extraction process may have affected performance. Design and fabrication of a demo-scale hydrolysis and fermentation system for direct conversion of industrial sweetpotatoes and sweet sorghum juice was completed. Physical properties of each of the biomass materials were measured for use in vessel design and material handling considerations. Hydrolysis and fermentation tanks were capable of agitation, temperature control, environmental parameter monitoring, material introduction, and sampling. Material flow logistics through the system and a suitable control scheme were designed.
Date: 2010-05-03
Degree: MS
Discipline: Biological and Agricultural Engineering

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