Eicosapentaenoic Acid Enrichment from Sardine Oil by Argentation Chromatography

Abstract

Eicosapentaenoic acid (EPA) derived from chemically hydrolyzed sardine oil was concentrated by urea fractionation using methanol at different temperatures (2, 4, and 6 °C) and urea/fatty acid ratios (2:1, 3:1, and 4:1 w/w) and purified by argentation neutral alumina column chromatography. The individual fatty acids were determined as fatty acid methyl esters (FAME) by gas-liquid chromatography and gas chromatography-mass spectroscopy as FAME and N-acyl pyrrolidides. In the mass fragmentation pattern of FAME, the base peak was assigned to be the 1-methoxyethenol moiety (m/ z) 74 obtained by McLafferty rearrangement. Formation of the cyclic tropylium ion (m/ z) 91 in fatty acids with four or more double bonds was apparent in FAME-PUFAs. The base peak of N-acyl pyrrolidides was the McLafferty rearrangement ion, 1-(pyrrolidin-1-yl)ethenol (m/ z) 113. The highest concentration of EPA (47.78%) was obtained at the crystallization temperature of 4 °C with a urea/fatty acid ratio of 4:1 (w/w) with 93.74% yield. After complexation of saturated and less unsaturated fatty acids by urea complexation, argentation chromatography resulted in an EPA of high purity (99.6%) with an overall recovery of 54.09% using 50% diethyl ether/ n-hexane as eluting solvent. The peroxide (POV) and thiobarbituric acid (TBS) values were found to be highest (4.0 mequiv of O2/kg and 5.2 mg of malondialdehyde/kg, respectively) during urea fractionation at the higher crystallization temperature (6 °C) and higher urea/fatty acid ratio (4:1).