The Use of Argentation Chromatography for the Analysis of Fatty Acid Esters of Polyenes: The Structure of Carotenoid Esters of Aglais urticae (Lepidoptera, Insecta)

Abstract

Abstract Argentation Thin-layer systems for argentation chromatography of fatty-acid esters of carotenoids have been developed. As two-dimensional reversed-phase partition system on paraffine impregnated cellulose this method permits a clear discrimination between saturated and unsaturated fatty acids. By adsorption on silver nitrate containing silica gel-G separation of carotenoid esters according to the degree of unsaturation of their fatty acids was established. With the use of known esters for comparison the fatty acids of whole carotenoid esters can be successfully analysed from minute amounts. Using these methods the carotenoid esters of pupae of Aglais urticae have been studied. The pupae contain 5.3% β-carotene, 46% lutein diester, 7.8% lutein 3-monoester, 11.7% lutein 3′-mono-ester, and 29.2% unesterified lutein. The fatty acids of the esters are linoleic acid (18:2) and linolenic acid (18:3) only. The diester fraction was composed of 70% dilinolenate, 25% linolenate-linoleate, and 5% dilinoleate. The combined monoesters consisted of 81% linolenate and 19% linoleate. The two main diesters could be isolated in a preparative scale and their structure verified by mass spectrometry. On the whole, in Aglais pupae 6.2 μg linolenic acid and 1.4 μg linoleic acid are bound to lutein. Since polyunsaturated fatty acids are of dietary origin, and represent essential factors for insect development, it is concluded, that their esterification with carotenoids may be a mode of storage comparable to the formation of glycerides.