Abstract: The separation of glyceride fish oil high in omega-3 polyunsaturated fatty acid (ω-3 PUFA) produced by multistage enzymatic transesterification was studied by multistep molecular distillation. Firstly, glycerides and by-products in the transesterification products were separated by primary molecular distillation. When the distillation pressure was 5 Pa, the distillation temperature was 140 ℃, the scraper speed was 240 r/min, and the feeding rate was 0.2 mL/min, the yield of the first-stage heavy phase was 47.13% and the content of ω-3 PUFA in it was 53.76%. Meanwhile, high-temperature gas chromatography (HTGC) and nuclear magnetic resonance hydrogen (1H-NMR) spectroscopy consistently showed that the heavy phase did not contain fish oil ethyl ester. Secondly, the ω-3 PUFA content of the light phase increased from 60.73% to 78.01% by molecular distillation at a distillation pressure of 5 Pa, a distillation temperature of 110 ℃, a scraper speed of 240 r/min, and a condensation temperature of 20 ℃. After conducting secondary enzymatic transesterification reaction and molecular distillation separation on the enriched first-stage light phase, the yield of the second-stage heavy phase was 78.01% and its ω-3 PUFA content was 51.38%. When the enrichment step was omitted, the content of ω-3 PUFA in the second-stage heavy phase was only 42.37%. Multistep molecular distillation combined with multistage enzymatic transesterification can be used to prepare glyceride-type fish oil products with different ω-3 PUFA contents, with maximal utilization of raw materials and by-products.

Key words: enzymatic transesterification; molecular distillation; fish oil; ω-3 polyunsaturated fatty acid; glyceride