Highly sensitive determination of lipid components including polyunsaturated fatty acids in individual zooplankters by one-step thermally assisted hydrolysis and methylation-gas chromatography in the presence of trimethylsulfonium hydroxide

Abstract

Thermally assisted hydrolysis and methylation-gas chromatography (THM-GC) in the presence of trimethylsulfonium hydroxide (TMSH) was applied to the analysis of the lipid contents and their fatty acid compositions in individual zooplankters, especially focusing on polyunsaturated fatty acid (PUFA) components. On the resulting chromatograms, fatty acid components including PUFAs such as eicosapentaenoic acid (EPA; C20:5) and docosahexaenoic acid (DHA; C22:6) in single zooplankters were clearly observed as their methyl esters without doing any tedious and time-consuming pretreatment. By using this technique, the lipid contents and fatty acid compositions in a powdered plankter sample prepared by cryomilling homogenization were estimated on the basis of the observed peak intensities with relative standard deviations of less than 6%. The fatty acid compositions thus determined were in good agreement with those obtained by the conventional technique involving solvent extraction of the samples for every fatty acid component including PUFAs. The differences among individual zooplankter samples were then evaluated by THM-GC method. As a result, the chemical compositions of EPA and DHA showed relatively large inter-individual fluctuations even for the samples cultured under the same conditions. This suggests that lipid biosynthesis of the highly unsaturated fatty acid components and their consumption proceeded differently depending on the life history for each individual zooplankter.