ARS | Publication request: Producing Docosahexaenoic Acid (DHA)-Rich Algae from Biodiesel-Derived Crude Glycerol: Effects of Impurities on DHA Production and Algal Biomass Composition

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 16, 2008
Publication Date: May 9, 2008
Citation: Pyle, D.J., Garcia, R.A., Wen, Z. 2008. Producing Docosahexaenoic Acid (DHA)-Rich Algae from Biodiesel-Derived Crude Glycerol: Effects of Impurities on DHA Production and Algal Biomass Composition. Journal of Agricultural and Food Chemistry. 56(1):3933-3939.

Interpretive Summary: The rapid growth of the biodiesel industry has produced a severe glut of crude glycerol, the main co-product of the biodiesel manufacturing process. On the other hand, demand for fish oil, and the omega-3 fatty acids they contain, is increasingly outstripping supply. The present research involves using crude glycerol to grow algae that produce large amounts of one of the main omega-3 fatty acids found in fish oil. In order for this process to be effective, the algae should be able to utilize crude glycerol from different biodiesel plants, which vary significantly in composition, and produce large amounts of the omega-3 fatty acid, quickly. At the end of the process, the algae should be nutritious and free of toxic metals so that it can be used to supplement human or animal food. To these ends, crude glycerol from three sources was analyzed and it was shown that although they differ in composition, the algae grow on each of them similarly. Tests were performed to determine the optimal amount of glycerol to use when growing algae. Finally, analysis of algae from the end of the process showed that it has a nutritional composition that may be beneficial to animals in addition to its omega-3 fatty acid content, and that it is free of heavy metal contamination.

Technical Abstract: Crude glycerol is the primary byproduct of the biodiesel industry. Producing docosahexaenoic acid (DHA, 22:6 n-3) through fermentation of the alga Schizochytrium limacinum on crude glycerol provides a unique opportunity to utilize a large quantity of this byproduct. The objective of this work is to investigate the effects of impurities contained in the crude glycerol on DHA production and algal biomass composition. Crude glycerol streams were obtained from different biodiesel refineries. All the glycerol samples contained methanol, soaps, and various elements including calcium, phosphorus, potassium, silicon, sodium, and zinc. Both methanol and soap were found to negatively influence algal DHA production; these two impurities can be removed from culture medium by evaporation through autoclaving (for methanol) and by precipitation through pH adjustment (for soap). The glycerol-derived algal biomass contained 45-50% lipid, 14-20% protein, and 25% carbohydrate, with 8-13% ash content. Palmitic acid (C16:0) and DHA were the two major fatty acids in the algal lipid. The algal biomass was rich in lysine and cysteine, relative to many common feedstuffs. Elemental analysis by Inductively Coupled Plasma showed that boron, calcium, copper, iron, magnesium, phosphorus, potassium, silicon, sodium, and sulfur were present in the biomass, while no heavy metals (such as mercury) were detected in the algal biomass. Overall, the results show that crude glycerol was a suitable carbon source for algal fermentation. The crude glycerol-derived algal biomass had a high level of DHA and a nutritional profile similar to commercial algal biomass, suggesting a great potential for using crude-glycerol derived algae in omega-3 fortified food or feed.