Extraction of lipids from fermentation biomass using near-critical dimethylether

The extraction of lipids from both wet and dry biomass produced by fermentation has been carried out using near-critical dimethylether (DME) as the extraction solvent. Fermentations were carried out from a shake flask up to a 300 L scale using the microorganism Mortierella alpina, and up to a 20 L scale for Phaffia rhodozyma and Agrobacterium tumefaciens. The lipids extracted at a laboratory and pilot scale from the biomasses were enriched in arachidonic acid, astaxanthin, and co-enzyme Q10 respectively. Extractions were also performed on marine microalgae, produced by a proprietary fermentation process, to obtain lipids rich in EPA. Lipids were extracted from wet biomass using DME, which removes the need to dry the biomass. Water is also co-extracted, which has to be separated from the lipid. The biomass shrunk considerably during packed bed extraction of wet biomass, leading to channelling. Repacking and re-extraction of the packed bed enabled full lipid yields to be obtained. The extraction of lipids from biomass suspended in fermentation broth showed considerable promise, and lipid yields were improved due to the recovery of lipids that had been exuded into the broth from the microorganism. In contrast, the extraction of lipids from freeze-dried biomass using DME was routine, yields were substantially higher than using CO₂ or CO₂ + ethanol, but were lower than from wet biomass. DME also extracted polar lipids from both wet and dry biomass, leading to the higher total lipid yields compared to CO₂. Separate extraction of non-polar and polar lipids was possible by sequential extraction of dry biomass using initially CO₂ followed optionally with ethanol co-solvent; and then DME.