Effects of crop management on fatty acid profile of low-linolenic varieties

摘要

Rapeseed oil, rich in alpha-linolenic acid (C18:3) is easily oxidized when heated and therefore not suitable for deep frying. New rapeseed varieties produce oil with low linolenic acid content, which can vary from 1.5 to 4.5% between fields and years.According to Everard (2004), a typical unpleasant odour appears above a threshold content of 2.5% C18:3 when rapeseed oil is heated. Understanding the causes of linolenic acid content variability is therefore necessary to produce optimal oil quality. Fatty acid profile is affected by genotype and climatic conditions, especially temperature. However, crop management could also play a role, as there are differences among neighbour fields of the same cultivar, i.e. with similar climatic and genotypic background. Sowing density, sulphur fertilization, insect and disease control had no direct effect on fatty acid profile in the experiments carried out in Changins, VD, Switzerland, in 2004 and in 2005. However, they showed interesting relationships between several quality parameters of grain harvested (oil and protein content, oleic and linolenic acid content). Oil and protein content were strongly negatively correlated (r=-0.96) and both could partly explain variability of linolenic acid content with correlation coefficients r=0.34 and r=-0.42 for protein and oil, respectively. Nitrogen nutrition influenced oil content but its effect on fatty acid profile is not clear-cut. In 2004, one variety (Spiral)seemed to be sensitive to nitrogen fertilization with higher linolenic acid content at higher fertilization rates, whereas the cultivar Splendor did not show significant differences between 90, 130, 170 and 210 kg N/ha. This moderate direct effect of N fertilization can be perturbed by other indirect mechanisms mediated by temperature. High N fertilization may delay anthesis and consequently the period of high linolenic acid synthesis, which has been shown to be temperature sensitive (Baux et al., 2007). If minimal temperatures change during this period, the final oil composition may be affected. It is concluded, that crop management practices have only limited effects on fatty acid composition.