Date of Award

12-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biosystems Engineering

Advisor

Walkker, Terry H

Committee Member

Dawson , Paul L

Committee Member

Drapcho , Caye M

Committee Member

Toler , Joe E

Committee Member

Nghiem , Nhuan

Abstract

There is a growing awareness of health benefits of polyunsaturated fatty acids (PUFAs) e.g. arachidonic acid (ARA, C20:4n6) and eicosapentaenoic acid (EPA, C20:5n3). In general, plant seed oil and animal fat do not contains long-chain PUFAs with more than eighteen carbons. This study investigated the feasibility for addition of ARA and EPA to canola oil through the fermentation of fungi, Mortierella alpina, using canola flake, cake or meal as substrates. Supercritical CO2 extraction was also investigated for lipid extraction. In addition, a supercritical CO2 explosion process was characterized and applied to enhance oil extraction using supercritical CO2 and to potentially improve the digestibility of canola material for fungal conversion.
Three new PUFAs, γ-linolenic acid (GLA, γ-C18:3n6), ARA and EPA were added through the conversion of canola substrate with fungi Mortierella alpina. The conversion rate of fungi-digested lipids to fungi-produced lipids was estimated to be nearly 50%. ARA yields of 20.3 mg/g flake, 12.5 mg/g cake and 20.1 mg/g glucose, and EPA yields of 3.3 mg/g flake, 2.7 mg/g cake and 0.3 mg/g glucose were obtained in flask culture. When canola meal was used as substrate in combination with different oils, corn and olive oils produced higher ARA, and lower EPA than canola and soybean oils. Olive oil yielded the highest ARA content of 48.9 mg/g substrate, and canola oil yielded the highest EPA content of 5.7 mg/g substrate. When scaled up to 7-liter fermenter production using canola flake compared to glucose and yeast extracts, ARA yields of 19.8 mg/g flake (609 mg/l) and 82.8 mg/g glucose (2,900 mg/l), and EPA yields of 3.0 mg/g (99 mg/l) flake and 0.4 mg/g glucose (13 mg/l) were obtained. Mortierella alpina co-cultured with Pythium irregulare in flask culture improved the production with ARA yields to 26 mg/g flake, 23 mg/g cake and 38 mg/g glucose and EPA yields of 4.3 mg/g flake, 3.7 mg/g cake and 0.3 mg/g glucose.
Supercritical CO2 explosion at initial conditions in the ranges of 25 to 65°C and 500 to 3,000 psi was characterized based on total release time, rate of depressurization, and effect of phase change on the rate of depressurization. Oil extraction from canola flakes using supercritical CO2 was improved after the explosion treatment. Explosion at 35°C and 3,000 psi resulted in the highest oil yield with nearly 13% oil yield improvement. When the canola meal exploded under 65oC and 3,000 psi was utilized for fungal fermentation, the yields of ARA and EPA were enhanced. The exploded meal without autoclaving achieved the highest yields of ARA, 40.9 mg/g substrate and EPA, 5.1 mg/g substrate. The raw meal with autoclaving produced the lowest yields of ARA, 8.3 mg/g substrate and EPA, 0.8 mg/g substrate.

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Microbiology Commons

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