Docosahexaenoic acid (DHA) is a semi-essential polyunsaturated fatty acid (PUFA) for eukaryotic cells, found in natural sources such as fish and algal oils and widely used as ingredient for omega-3 containing foods or supplements. DHA effects are connected to its natural structure with six cis double bonds, but geometrical monotrans isomers can be formed during distillation or deodorization processes, as an unwanted event that alters molecular characteristics and annihilates health benefits. The characterization of the six monotrans DHA regioisomers is an open issue to address for analytical, biological and nutraceutical applications. Here we report the preparation, separation and first identification of each isomer by a dual approach consisting of: i) the direct thiyl radical-catalyzed isomerization of cis-DHA methyl ester, and ii) the two-steps synthesis from cis-DHA methyl ester via mono-epoxides as intermediates, which are separated and identified by bidimensional nuclear magnetic resonance spectroscopy, followed by elimination for the unequivocal assignment of the double bond position. This mono-trans DHA isomer library with NMR and GC analytical characterization was also used to examine the products of thiyl radical catalysed isomerization of a fish oil sample and to evaluate the trans isomer content in omega-3 containing supplements commercially available in Italy and Spain.
Trans Lipid Library: synthesis of docosahexaenoic acid (DHA) monotrans isomers and regioisomer identification in DHA-containing supplements
Menounou, Georgia;Giacometti, Giorgia;
2018
Abstract
Docosahexaenoic acid (DHA) is a semi-essential polyunsaturated fatty acid (PUFA) for eukaryotic cells, found in natural sources such as fish and algal oils and widely used as ingredient for omega-3 containing foods or supplements. DHA effects are connected to its natural structure with six cis double bonds, but geometrical monotrans isomers can be formed during distillation or deodorization processes, as an unwanted event that alters molecular characteristics and annihilates health benefits. The characterization of the six monotrans DHA regioisomers is an open issue to address for analytical, biological and nutraceutical applications. Here we report the preparation, separation and first identification of each isomer by a dual approach consisting of: i) the direct thiyl radical-catalyzed isomerization of cis-DHA methyl ester, and ii) the two-steps synthesis from cis-DHA methyl ester via mono-epoxides as intermediates, which are separated and identified by bidimensional nuclear magnetic resonance spectroscopy, followed by elimination for the unequivocal assignment of the double bond position. This mono-trans DHA isomer library with NMR and GC analytical characterization was also used to examine the products of thiyl radical catalysed isomerization of a fish oil sample and to evaluate the trans isomer content in omega-3 containing supplements commercially available in Italy and Spain.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
