A Novel Urea Complexation Method for Enrichment of n-3 Polyunsaturated Fatty Acids

A novel urea complexation technology was developed based on the agglomeration phenomenon induced by ambient-temperature agitation of a ternary system consisting of urea, water and fatty acid ethyl esters (EEs). The agglomeration phenomenon can be regarded as an intuitive indicator to judge the occurrence of urea complexation. Using docosahexaenoic acid (DHA) containing EE (DHA-EE) from Crypthecodinium cohnii oil as the substrate, key variables including agglomeration time, urea/DHA-EE ratio, water/DHA-EE ratio, and temperature were investigated. The urea complexation predominantly occurred within 15 min following agglomerate formation. Temperature in the range of 0–40°C exerted no significant effect on the yield of the non-urea-complexed fraction or its DHA content, enabling the operation to be conducted at room temperature without heating or cooling. Under unoptimized conditions, the proposed method effectively increased the DHA content of EE from Crypthecodinium cohnii oil from 40.73% to 89.87%. For EE from Schizochytrium sp. oil, the contents of DHA and docosapentaenoic acid were improved from 47.17% and 13.93% to 69.30% and 20.29%, respectively. Meanwhile, the contents of eicosapentaenoic acid and DHA in two EE form fish oils were enhanced from 18.26% and 11.76% to 34.86% and 22.96%, and from 13.30% and 57.24% to 15.66% and 68.68%, respectively. The present study provided a novel technical pathway for the efficient enrichment of polyunsaturated fatty acids.