The effects of different extraction methods of lipids from Nannochloropsis oceanica on the contents of omega-3 fatty acids

Abstract

Nannochloropsis species are promising producers of the omega-3 fatty acid, eicosapentaenoic acid (EPA) of high interest for the food, nutraceutical and pharmaceutical industries. These applications demand the use of safer and food grade solvents. In this study, different solvent systems, including chloroform/methanol (CM), dichloromethane/methanol (DM), dichloromethane/ethanol (DE) and ethanol, were investigated as means of producing EPA-enriched lipid extracts from Nannochloropsis oceanica spray-dried biomass. Emphasis was given to the application of food grade ethanol, and ultrasound treatment was investigated as a means to increase lipid recovery during ethanol extraction. Total lipid extracts recovered with the different solvent systems were assessed by gravimetry and their lipid recovery efficiency determined by a purification process. The fatty acid composition of the total lipid extracts, particularly the EPA content, was determined by GC–MS.Of the various solvent systems tested the conventional CM and DM gave the highest yields with similar extraction efficiency followed by DE. Extraction with ethanol provided a total lipid extract of 19.1% dry biomass. Nevertheless, the combination of ethanol extraction with ultrasound treatment increased lipid yields, with an ultrasound probe providing the best results. The highest EPA content was obtained with CM and DM solvent systems followed by ethanol extraction assisted by ultrasound probe which increased EPA content by 35% relative to extraction with only ethanol, and comparable to that obtained with CM. These results indicate, for the first time, ethanol extraction assisted by ultrasound probe as a promising low toxicity, food grade and environmentally friendly approach to obtain EPA-enriched lipid extracts from N. oceanica biomass.