Obtaining eicosapentaenoic acid-enriched polar lipids from microalga Nannochloropsis sp. by lipase-catalysed hydrolysis

The aim of this work was to increase the eicosapentaenoic acid (EPA) content of saponifiable lipids (SLs) extracted from the microalga Nannochloropsis sp. These SLs are rich in polar lipids (50.2 % glycolipids [GLs] and 27.4 % phospholipids [PL] of the total SLs). The EPA enrichment was carried out by selective enzyme-catalysed hydrolysis, based on the discrimination that some lipases show towards EPA, which is hydrolysed at a lower velocity and remains in the original polar lipids in greater proportion than other fatty acids. Initially, nine enzymes and eight solvents (all permitted in the food industry) were tested as reaction media. Lipase QLM from Alcaligenes sp. and acetone proved the most effective reaction medium to concentrate EPA. Studies were carried out on the influence of the hydrolysis time, lipase QLM immobilization, its reutilization, the scaling-up of the hydrolysis reaction and the influence of the polar lipid content. The maximum EPA content (or EPA concentration factor, FC) was obtained using lipase QLM immobilized on Accurel MP 1000 (a lipase/SL ratio of 1:1 [w/w] or an immobilized lipase/SL ratio of 2.5:1 [w/w]), 50 mL acetone/g SLs, a water/SL ratio of 2.8:1 (w/w), at 40 °C, 300 rpm (in flasks with orbital shaking), and 24 h of hydrolysis time. Under these conditions, polar lipids with up to 70 % EPA (starting from a microalgal polar lipid concentrate containing 48.5 % EPA) and an EPA recovery of 92 % were achieved. These hydrolytic conditions were also applied to increase the EPA content of microalgal SLs that had an even richer polar lipid content (90.3 %). Using this substrate, polar lipids with 68.7 % EPA and an EPA recovery of 98 % were achieved.