Abstract
Nannochloropsis oceanica can accumulate lipids and is a good source of polar lipids, which are emerging as new value-added compounds with high commercial value for the food, nutraceutical, and pharmaceutical industries. Some applications may limit the extraction solvents, such as food applications that require safe food-grade solvents, such as ethanol. However, the effect of using ethanol as an extraction solvent on the quality of the extracted polar lipidome, compared to other more traditional methods, is not yet well established. In this study, the polar lipid profile of N. oceanica extracts was obtained using different solvents, including chloroform/methanol (CM), dichloromethane/methanol (DM), dichloromethane/ethanol (DE), and ethanol (E), and evaluated by modern lipidomic methods using LC-MS/MS. Ultrasonic bath (E + USB)- and ultrasonic probe (E + USP)-assisted methodologies were implemented to increase the lipid extraction yields using ethanol. The polar lipid signature and antioxidant activity of DM, E + USB, and E + USP resemble conventional CM, demonstrating a similar extraction efficiency, while the DE and ethanol extracts were significantly different. Our results showed the impact of different extraction solvents in the polar lipid composition of the final extracts and demonstrated the feasibility of E + USB and E + USP as safe and food-grade sources of polar lipids, with the potential for high-added-value biotechnological applications.
Highlights
Microalgae are emerging as a valuable source of lipids for biotechnological applications
A total of 128 lipid species were identified in N. oceanica lipid extracts by retention time, mass accuracy, and MS/MS data (Supplementary Materials, Table S1), including 15 monogalactosyl diacylglycerol (MGDG), 5 monogalactosyl monoacylglycerol (MGMG), 14 digalactosyl diacylglycerol (DGDG), 2 digalactosyl monoacylglycerol (DGMG), 10 sulfoquinovosyl diacylglycerol (SQDG), 1 sulfoquinovosyl monoacylglycerol (SQMG), 19 diacylglyceryl-N,N,N-trimethyl homoserine (DGTS), 4 monoacylglycerylN,N,N-trimethyl homoserine (MGTS), 11 phosphatidylglycerol (PG), 6 phosphatidylinositol (PI), 10 phosphatidylethanolamine (PE), 20 phosphatidylcholine (PC), 9 lyso phosphatidylcholine (LPC), and 2 phosphoinositol ceramide (PI-Cer) species
The polar lipid species identified in this study have all been previously reported in the literature for Nannochloropsis species, including N. oceanica [6,36,37,38,39,40], except for the DGMG(16:1), DGMG(16:0), LPC(14:0), LPC(16:2), LPC(18:3), and PC(36:7) lipid species, which are reported here for the first time
Summary
Microalgae are emerging as a valuable source of lipids for biotechnological applications. Omega-3 PUFAs such as EPA are essential in the human diet and important components of lipids, especially in certain organs, such as the central nervous system, playing a beneficial role in the neuronal, retinal, and immune system. They are precursors of resolving eicosanoids and with a well-recognized important role in the regulation of inflammation [3]. This autotrophic microalga accumulates omega-3 PUFAs mainly in polar lipids, such as betaine lipids, glycolipids, and phospholipids [4,5,6,7], which are the main components of cells, thylakoids, and chloroplast membranes. In N. oceanica, polar lipids are generally rich in long-chain omega-3 PUFAs (mainly EPA), of high nutritional value, being glycolipids, followed by betaine lipids and phospholipids, which are richer in this omega-3 PUFA than triglycerides [2]
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