BATCH ENZYMATIC SYNTHESIS, CHARACTERIZATION AND OXIDATIVE STABILITY OF DHA-CONTAINING STRUCTURED LIPIDS

Abstract

Fortification of processed foods with n-3 polyunsaturated fatty acids (n-3 PUFA) is rarely practiced in North America. This study utilized, DHA single cell oil (DHASCO), an algal source of PUFA (docosahexaenoic acid, DHA), for the synthesis of structured lipids (SL) and compared the oxidative stability and melting characteristics of the products with those of native DHASCO as control. Immobilized lipase, IM60 from Rhizomucor miehei was the biocatalyst. DHASCO was modified with caprylic, oleic, or stearic acids as acyl donors, in a stirred-batch reactor, to produce three different SL. The reactions were performed at 55C for 48 h in n-hexane for caprylic and oleic acid SL, and at 60C for stearic acid-SL. Mole ratio of substrates were 1:6 for DHASCO-C8:0, 1:2 for DHASCO-C18:1, and 1:1 for DHASCO-C18:0. Mol% incorporation and the fatty acids at the sn-2 position of the SL were determined by gas chromatography (GC). After DHASCO oil modification, mol% of the incorporated fatty acids were 47.6, 46.3 and 31.2 for C8:0, C18:1, and C18:0-containing SL, respectively. Alkaline extraction was a better deacidification method than short-path distillation, and reduced free fatty acid levels to 0.3% in all SL. DHA was the predominant fatty acid at the sn-2 position in all the SL. DHASCO melting peak was -10.6C. The melting peaks for the SL were -10 and -6.2C for oleic-SL, -8.1 and -0.7C for caprylic-SL, and 16.0, 20.4, and 34.4C for stearic-SL. Oxidative stability studies showed that SL were less stable to oxidation than DHASCO, with DHASCO-18:0 being the most susceptible. With the addition of adequate antioxidants, such SL products synthesized from DHASCO will be stabilized and may be useful in DHA fortification of processed foods such as nutrition bars, dressings, infant formula or in functional foods.