Semester

Fall

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Kristen E Matak

Abstract

Docosahexaenoic acid (DHA), an omega-3 fatty acid found in cold-water fish, has positive health benefits. While the suggested amount of 220 mg/day for adults may be attained by consuming fish, this may increase exposure to environmental pollutants. The heterotrophic marine alga Crypthecodinium cohnii is an important source of DHA because C. cohnii can accumulate lipid greater than 20% of their biomass with a large fraction of DHA (30-50%). Commercially, DHA production by C. cohnii is conducted in large bioreactors (∼100 m3 capacity) using a batch-mode process. The purpose of this study was to investigate lipid and DHA production by C. cohnii using batch-mode and continuous-mode processes. The long term objective is to maximize DHA production from a safe and reliable marine source.;Batch cultivation of C. cohnii was carried in a 15 L bioreactor vessel at 27°C. C. cohnii (ATCC 30772) was grown in ATCC complex media 460 for 10 days at 25°C, transferred to simple media (9 g/L glucose, 2 g/L yeast, and 25 g/L salt) and incubated statically for 8 days at 25°C. Cultures were subsequently transferred to larger volumes of simple media and incubated at 25°C in an orbital shaker incubator at 100 rpm. At each transfer, a 10% (v/v) inoculum level was maintained. Cultivation of C. cohnii was conducted in a 15 L computer controlled bioreactor vessel. Temperature was maintained at 27°C by a computer controlled heating jacket. A 25% glucose solution was administered continuously at a rate of 0.78 mL/min.;Continuous cultivation of C. cohnii was conducted in two 15 L computer controlled bioreactor vessels. Temperature of both vessels was maintained at 27°C during the growth mode of the study and standard media (25g/L glucose, 5.5g/L yeast, and 25 g/L salt) was administered to both bioreactors. After 40 h, the system was switched to "continuous" mode where one vessel was maintained as a growth vessel at 27°C, and the other as a lipid accumulation vessel at 17°C. In continuous mode, standard media was administered to the growth vessel and a 25% glucose solution was administered to the lipid accumulation vessel.;In both studies algal growth was monitored spectrophotometrically and measured every 12 h at 470 nm. The biomass concentration, lipid content and fatty acid profile were determined by harvesting samples from the vessel.;Results of the study showed that C. cohnii growth was achieved in batch-mode and continuous-mode cultivation with lipid and DHA production. Maximum values for volumetric DHA productivity, biomass, lipid and DHA concentrations in the batch study were 3.61 mg/L.h, 8.35 g/L, 0.89 g/L and 0.32 g/L respectively. In continuous study the maximum values were 4.132 mg/L.h, 3.75 g/L, 0.55 g/L and 0.145 g/L respectively. Although DHA concentration was higher in the batch mode process, volumetric DHA productivity of continuous mode process exceed volumetric DHA productivity of batch mode because of higher production rate of continuous mode process. These values did not exceed the reported values of other batch processes that used a 50% glucose feed. More research is needed to optimize processing parameters in continuous mode to produce a viable alternative to batch mode processes.

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