The characterization and biodegradation of aspen steryl esters and waxes

• Main Author: Leone, Robert Danny
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/8190

Steryl esters and waxes are major contributors to pitch deposition when aspen is pulped. To overcome this problem attempts have been made to identify these compounds. The first part of this thesis focuses on the identification of these compounds using gas chromatography-mass spectrometry (GC-MS). Since the GC-MS analysis of the aspen steryl esters and waxes is a difficult task, we have only been able to identify lupeol palmitate and lupeol linoleate so far. The steryl esters and waxes fraction was hydrolyzed and the identity of the resulting sterol and fatty acid moieties established by GC-MS. β-sitosterol and β-amyrin were the two primary sterol moieties making up 34.7% and 37.5% of this fraction, respectively. Palmitic acid (C1 6:0) was the most abundant fatty acid making up 49.2% of the total acid material while linoleic acid (C1 8:2), a prominent unsaturated fatty acid in other lipid constituents, comprised 31.8% of the fatty acids in the steryl esters and waxes fraction. Standard steryl esters and waxes such as β-sitosterol palmitate and lupeol stearate were synthesized from the major hydrolyzed sterols and fatty acids identified. The aspen steryl esters and waxes fraction was spiked with the synthesized standards to confirm where these compounds eluted in the complex GC-FID chromatogram of the aspen steryl esters and waxes. The objective of the second part of this thesis was to determine whether some wood-inhabiting fungi were capable of degrading the aspen steryl esters and waxes. Fungi that effectively degrade these compounds could possibly be used as biological treatment agents to remove steryl esters and waxes from aspen wood prior to pulping. Aspergillus luchuensis and Cunninghamella elegans were the two most effective fungi in the degradation of aspen steryl esters and waxes in liquid culture, consuming 3.0 and 2.2 mg/mL in 7 days, respectively. These fungi grew by hydrolyzing the steryl esters and waxes into their sterol and fatty acid components. A. luchuensis and C. elegans were also grown on steryl esters and waxes in the presence of glucose or triglycerides in order to understand how these organisms behaved on complex substrates such as aspen wood. As expected, both fungi consumed the glucose prior to modifying the steryl esters and waxes. The amount of steryl esters and waxes consumed by A luchuensis and C. elegans was not affected by the addition of glucose. In the steryl esters and waxes cultures supplemented with triglycerides, A. luchuensis and C. elegans appeared to consume both carbon sources simultaneously.