Photooxidative degradation of annual rye-grass straw to substrates enhansing rhodotorula mucilaginosa growth Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/js956j933

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  • Annual ryegrass (Lolium multiflorum) is a major seed crop in the Willamette Valley of Oregon. Persistent crop diseases have necessitated annual field burning to protect future crops. This practice, while very effective for disease eradication, produces large quantities of air polluting smoke in the valley and a general wastage of a material which could be used in the manufacture of economically important products. The cellulosic portion of straw is susceptible to microbial dissimilation but the lignin fraction (10-14%) is extremely resistant. Modification of the straw to relieve this resistance would be valuable in the biological utilization of straw and, under controlled conditions, the modified components could be used as substrates for microbial growth in the production of single cell protein. Ryegrass straw hydrolysed with 3% sulfuric acid at 121 C, homogenized to a fine consistency and then Soxhlet extracted with hot water prior to irradiation was subjected as a 1. 0% w/v suspension to photooxidation with ultraviolet light and gaseous oxygen for 5 hour intervals to a maximum of 30 hours. After each photooxidation period the photolyzate was removed and subjected to both chemical analyses and growth by Rhodotorula mucilaginosa, a non-lignin utilizing yeast. Gas-liquid chromatography-Rapid-Scan mass spectrometry and gas-liquid chromatography were used to determine straw photooxidation products. Glyceraldehyde, erythrose, threose, arabinose, xylose, mannose, rhamnose and glucose were identified. All compounds isolated were utilized by the Rhodotorule. strain. The appearance of glyceraldehyde, erythrose and threose which are not normally found in straw suggested a 1-carbon photodecomposition of arabinose and xylose leading to erythrose and threose. Glyceraldehyde would result from a 1-carbon photodecomposition of erythrose and threose. Photodecomposition of the C₃ side chain in the C₃-C₆ lignin phenylpropanoid structure may be an additional source of glyceraldehyde. Ryegrass straw lignin concentration decreased from 33% to 12% after 12 hours photooxidation suggesting a demethoxylation of the phenylpropanoid structure and a concomitant increase in sulfuric acid solubility. Extensive photodecomposition of the C₃-C₆ lignin structure was ruled out because the concentrations of aromatic nuclei and phenolic hydroxyl groups were only 0. 09% and 0.43% respectively and considered to be insignificant levels. The ability of Rhodotorula mucilaginosa to utilize the photooxidation products obtained indicates that this type of treatment of recalcitrant materials can greatly improve biological utilization. A similar approach on other recalcitrant materials using different oxidizing agents and systems should be explored.
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