An analytical and breeding study on fatty acids in summer turnip rape (brassica campestris L. var. annua)

Abstract

The fatty acid composition of the seed oil of summer turnip rape (Brassica campestris L. var. annua) was investigated by gas liquid chromatography (GLC). The reliability of conventional sampling methods in capillary GC was compared with that of the new on column and PTV (programmed temperature vaporizer) techniques, with particular reference to the determination of fatty acid variation. In order to develop new, well-adapted turnip rape strains with improved oil quality, a breeding programme for a higher linoleic acid content, based on individual plant selection, was performed in 1978—85. The results showed that the conventional sampling techniques involving sample transfer to a hot injector were very unreliable as regards precision and accuracy. This was especially the case in the determination of trace fatty acid levels. The PTV methods with splitless and solvent split mode were as precise as cold on-column injection. The PTV sampling modifications, which are all superior to classical techniques, were even more suitable for routine analyses than on-column injection, where several restrictions are met. The analytical error with PTV for most of the compounds represented less than 1 % of the variation found for fatty acids within a turnip rape variety. The breeding experiments indicated that the level of linoleic acid can be increased under open-pollinated conditions in the field without affecting the α-linolenic acid content. The greenhouse conditions, on the other hand, were found to have a considerable environmental influence on the variation of these compounds, resulting in no response to linoleic-acid selection. In field trials, several strains with yields comparable to the varieties commonly cultivated in Finland were selected with a higher linoleic acid content (up to25 %). Most of them also contained no erucic acid. The new evidence concerning its beneficial physiological effects indicate that rapeseed oil should be considered as a serious alternative among sources of essential fatty acids. Such aspects should also be taken into account in future breeding of rapeseed fatty acids.