Model optimization-based enzymatic hydrolysis combined with molecular distillation for DHA enrichment from microalgal lipids

Developing an appropriate concentration strategy based on the characteristics of algal oil feedstock is crucial for preparing high-concentration premium glyceride-type docosahexaenoic acid (DHA). This study employed Aspergillus Oryzae (AO) lipase hydrolysis combined with molecular distillation (MD) to concentrate DHA in microalgae oil. Under the optimal reaction conditions for AO lipase, the hydrolysis reached equilibrium after 8 h, with the stable lipid composition, in which TAG and DAG accounted for 50.1 % and 21.9 % of the total lipids, respectively, with DHA content in TAG and DAG reaching 86.8 %. A finite difference model was employed to optimize the evaporation temperature, identifying the optimal temperature as 185 °C. At this temperature, MD experiments on the enzymatic hydrolysis products increased the DHA content in the retentate from 41 % in the initial oil to 49 %, with a concentration factor of 1.21 as well as a DHA recovery rate of 93.8 %. Furthermore, a second-stage enzymatic hydrolysis combined with MD on the first-stage retentate product elevated the DHA content to 60.9 %, achieving a final concentration factor of 1.49. Lipid as well as fatty acid composition analysis exhibited DHA content variation on the glycerol backbone, and the hydrolysis mechanism of AO lipase was preliminarily clarified. The enzyme hydrolyzes small molecular fatty acids, enriching large molecular polyunsaturated fatty acids (DHA) in TAG and DAG, which are then collected in the retentate via MD, achieving high DHA concentration.