Abstract
Improved methods for the extraction of eicosapentaenoic acid (EPA), an essential and economically important polyunsaturated fatty acid, are urgently required. However, lipid extraction rates using food-grade solvents such as ethanol are usually low. To improve the ethanol-based extraction rate, and to elucidate the relevant mechanisms, we used cellulase and laccase to treat powdered Nannochloropsis, one of the most promising microalgal sources of EPA. Cellulase and laccase synergistically increased lipid yields by 69.31% and lipid EPA content by 42.63%, by degrading the amorphous hemicellulose and cellulose, improving crystallinity, and promoting the release and extraction of lysodiacylglyceryltrimethylhomoserine. Scanning electron microscopy showed that cell morphology was substantially altered, with cell-wall rupture, loss of cell boundaries, and the release of intracellular substances. In conclusion, Nannochloropsis lipid yields may be directly linked to cell-wall hemicellulose structure, and enzymatic treatment to alter this may improve lipid yields.
Highlights
Conventional lipid-extraction methods, using food-grade solvents such as ethanol, typically produce low yields
Given the increasing market demands for lipids, better extraction methods are urgently required. This is true for eicosapentaenoic acid (EPA), an essential ω-3 polyunsaturated fatty acid with many critical nutritional functions in humans
Compared with the control group, cellulase and laccase increased lipid yields by 17.01% and 14.63%, respectively
Summary
Conventional lipid-extraction methods, using food-grade solvents such as ethanol, typically produce low yields. Given the increasing market demands for lipids, better extraction methods are urgently required This is true for eicosapentaenoic acid (EPA), an essential ω-3 polyunsaturated fatty acid with many critical nutritional functions in humans. Nannochloropsis primarily synthesizes polar lipids, including glycolipids, phospholipids, and betaine lipids, which form the cell membrane [10]. The thin trilaminar cell wall contains little lignin, but contains the highly aliphatic algaenan [22,25], an insoluble and non-hydrolysable biopolymer comprising long-chain aliphatic hydrocarbons bound by ether cross-linking reactions [26,27,28] These hydrocarbons are highly resistant to alkali or acid hydrolysis and water or organic-solvent solubilization [29], making lipid extraction from Nannochloropsis difficult. We further examine how lipid extraction alters cell wall structure, and the mechanisms whereby these enzymes promote lipid extraction
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