Cholesteryl esters from squid oil contain only saturated fatty acids, whereas the oil is rich in EPA and DHA and contains almost no saturated fatty acids

Abstract

Crude squid oil is a valuable source for docosahexaenoic acid (DHA). It represents a sustainable alternative to tuna oil, which has been so far the major source for DHA. During the development of an industrial process from squid oil to omega‐3 enriched ethyl esters, a solid powdery material was isolated from the residue obtained after short path distillation of ethyl esters, as a 0.3–0.5% weight/weight versus the starting crude oil. The isolated material and the products obtained by its methanolysis were characterized and structurally verified by TLC, 1H‐ and 13C‐NMR, as well as GC analysis. The material was found to be a mixture of cholesteryl esters, whose fatty acid profile mainly features C14:0, C16:0, and C18:0 along with minor amounts of C15:0 and C17:0 entities. No unsaturated acids are visible in the GC profile, whereas squid oil is rich in mono‐ and polyunsaturated acids. Isolation of total cholesteryl esters from the distillation residue by column chromatography rules out selective precipitation as a cause for the presence of only saturated fatty acids in the isolated solid. It is concluded that the cholesteryl esters containing only saturated acids are biosynthesized in the squids.Practical applications: The results presented in this publication may contribute to the general understanding of squid lipid metabolism. Moreover, quantitative analysis of cholesteryl esters in squid oil is relevant to the development of industrial methods for removal of all cholesterol in final products. The total cholesterol in crude squid oil is ca. 4%. Cholesteryl esters which are identified only in the distillation residue represent approximately 0.25% of total cholesterol in the crude squid oil. The scarce amount of esterified cholesterol indicates that it can be neglected when a process is optimized in order to lower total cholesterol in final products, whereas removal of free cholesterol must be focused. Finally, data show that: a) cholesteryl esters are less reactive than triglycerides during ethanolysis of squid oil, in agreement with published data; b) free cholesterol does not react with ethyl esters to give cholesteryl esters under ethanolysis conditions.Gas chromatograms of fatty acid methyl esters (fame) from squid cholesteryl esters (top) and squid crude oil (down).