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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.
Highlights
The cultivation of oil plants as the most economic way of producing fats has considerably increased during the last decades along with the development of cultivation techniques and industrial processing know-how
A gas chromatogram of the fatty acids in traditional rapeseed oil is presented in Fig. 1 (III)
The resuits obtained following the esterification of triolein, which is a compound where the acyl groups are formed only from oleic acid (18: lw9), showed that neither the esterification method nor gas chromatography resulted in the conversion of oleic acid to vaccenic acid (HI)
Summary
The cultivation of oil plants as the most economic way of producing fats has considerably increased during the last decades along with the development of cultivation techniques and industrial processing know-how. Soybean holds first place among oilseeds, accounting for one third of the world’s production of vegetable oil. It is followed in importance by oil palm, sunflower and rapeseed (Brassica sp.). Due to its excellent adaptability to different climatic conditions, rapeseed has enabled vegetable oil to be produced in areas ever further to the north. This expansion has been speeded up by compositional improvements achieved through intensive breeding such as elimination of erucic acid (22: lw9) from the oil, and reduction of the glucosinolate content in the meal (Downey 1983, Pigden 1983, Fochem 1985).
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