Effects of temperature on low-linolenic rapeseed oil fatty-acid composition

摘要

Rapeseed oil, rich in alpha-linolenic acid (C18:3), is easily oxidized when heated and therefore not suitable for deep frying.According to Everard (2004), the typical unpleasant < room odor > appears above a threshold content of 2.5 % C18:3, while its content varies around 8 to 10% in usually grown double-low varieties. Low-linolenic varieties with C18:3 content lower than 3.5% have been selected, but a large variability is still observed among locations and years. In order to meet the target content of 2.5 %, it is important to identify factors affecting the fatty acid profile of oilseed rape. Fatty acid composition is affected by environmental conditions, temperature being the main factor. Merrien (2005) showed for conventional rapeseed varieties that low minimal temperatures during the 60 days following the onset of flowering are related to high linolenic acid content with R2=0.37. Monitoring the fatty acid profile of low-linolenic varieties from the beginning of grain filling to maturity showed that linolenic acid synthesis occurs mainly between 550 and 850 degreelays after the onset of flowering, that is during the 20 first days of grain filling in Swiss conditions, i.e. 40 to 60 days after the onset of flowering. During this period, the correlation between final linolenic acid content and minimal temperature is even better, with R2=0.87. An easier way to show this relationship is based on the assumption that fatty acid desaturases regulated by temperature are active at low temperatures only. It consists in counting how many times during this period daily minimal temperature reaches a lower level than a threshold temperature of 13°C. The correlation between final linolenic acid content and number of days with minimal temperature below 13°C is as good as the one presented before, i.e. R2=0.85. It could also be used as a very simple predictive model and showed a good accuracy in 2005 in Changins.