Extraction of lipids from New Zealand fern fronds using near-critical dimethyl ether and dimethyl ether–water–ethanol mixtures

Abstract

Dimethyl ether (DME), under near-critical conditions, can be used to extract lipids containing valuable fatty acids from wet biomass. In this work, DME, and a mixture of DME with a water–ethanol co-solvent, are used to extract fronds of the fern Cyathea dealbata, and the fatty acid composition of the extract was compared with the fern total lipids obtained by chloroform–methanol extraction. Extraction was carried out by circulating DME through a packed bed of milled undried fern material at pressure of 4.0 MPa, temperature of 58 °C, flow rate of 13.6 kg per kg undried fern material per hour, for 60 min followed by extraction using DME with addition of 5 wt% of a 70% ethanol in water co-solvent mixture until 572 g of co-solvent had been introduced. The total combined yield of DME and DME–ethanol–water extracts was 6.3 wt% of the fronds with the recovery of 88–93% of the major fatty acids (18:3n-3, 16:0, 18:2n-6, 18:1n-9). The remaining residue contained<7% of the fern total lipids. The extracts were slightly enriched in eicosapentaenoic acid (EPA, 95% recovery), while a significant portion of arachidonic acid (ARA, 19%) remained in the residue. The DME and DME–ethanol–water extracts contained 6.9 and 6.1 mg/g of ARA, and 13.4 and 14.2 mg/g of EPA, respectively.