Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2009
Publication Date: 3/6/2009
Citation: Athalye, S.K., Garcia, R.A., Wen, Z. 2009. Use of Biodiesel-Derived Crude Glycerol for Producing Eicosapentaenoic Acid (EPA) by the Fungus Pythium irregulare. Journal of Agricultural and Food Chemistry. 57(7):2739-2744. Interpretive Summary: Biodiesel production inevitably yields crude glycerol as a low value byproduct. This glycerol is too impure for many practical applications, however, it has been shown to have potential as energy source for microorganisms in fermentations. A fungal organism which produces EPA, a valuable omega-3 fatty acid, has recently been shown to be capable of growing on crude glycerol. In this research, we found that under appropriate conditions, the fungal organism will produce high levels of EPA. The major impurities contained in crude glycerol, soap and methanol, were shown to be inhibitory to the growth of the fungal organism, but simple steps can be taken to remove these impurities. It was also found that the addition of vegetable oil to the medium enhances the growth and omega-3 production of the organism. The entire mass of the fungal organism was analyzed for several characteristics and was shown to have potential as an value–added animal feed supplement to be used in situations where enhanced omega-3 content is desired.
Technical Abstract: Crude glycerol is a major byproduct for the biodiesel industry. Producing value-added products through microbial fermentation on crude glycerol provides opportunities to utilize a large quantity of this byproduct. The objective of this study is to explore the potential of using crude glycerol for producing eicosapentaenoic acid (EPA, 20:5 n-3) by the fungus Pythium irregulare. When P. irregulare was grown in medium containing 30 g/L crude glycerol and 10 g/L yeast extract, EPA yield and productivity reached 90 mg/L and 14.9 mg/L-day, respectively. Adding pure vegetable oils (flaxseed oil and soybean oil) to the culture greatly enhanced the biomass and the EPA production. This enhancement was due to the oil absorption by the fungal cells and elongation of shorter chain fatty acids (e.g., linoleic acid and alpha-linolenic acid) into longer chain fatty acid (e.g. EPA). The major impurities contained in crude glycerol, soap and methanol, were inhibitory to fungal growth. Soap can be precipitated from the liquid medium through pH adjustment while methanol can be evaporated from the medium during autoclaving. The glycerol-derived fungal biomass contained about 15% lipid, 36% protein, and 40% carbohydrate, with 9% ash. In addition to EPA, the fungal biomass was also rich in the essential amino acids lysine, arginine and leucine, relative to many common feedstuffs. Elemental analysis by Inductively Coupled Plasma showed that aluminum, calcium, copper, iron, magnesium, manganese phosphorus, potassium, silicon, sodium, and sulfur, and zinc were present in the biomass, while no heavy metals (such as mercury and lead) were detected. The results show that it is feasible to use crude glycerol for producing fungal biomass that can serve as EPA fortified food or feed.