Sunflower seed fatty acid modification

Biodiesel (fatty acid methyl ester (FAME)) production is based on transesterification of vegetable oils and fats through the addition of methanol (or other alcohols) and a catalyst, giving glycerol as a by-product (which can be used for cosmetics, medicines and food). Oil-seed crops include rapeseeds, sunflower seeds, soy beans and palm oil seeds, from which the oil is extracted chemically or mechanically. Biodiesel can be used in 5%-20% blends with conventional diesel, or even in pure form, which requires slight modifications in the vehicle. 

The characteristic fatty acid patterns of plant triacylglycerols are to some extent under genetic control (see Section VI). In addition, environmental factors may modify the basic patterns, the extent of modification depending on the species. Thus the seed oils of plants grown in cool climates tend to be more unsaturated than those grown in warm climates (Hitchcock and Nichols, 1971). The chief influence seems to be on the characteristic fatty acid of the seed, so that for example in flaxseed oil there is a marked decline in the proportion of linolenic acid between 10° and 30°C and a corresponding increase in the proportion of its precursor, oleic acid (Canvin, 1965). Similarly, the proportion of linoleic acid in sunflower seed oil steadily declines between 10° and 30°C, to be replaced by oleic acid. Yet the linoleic content of safflower and the ricinoleic acid of castor are unaffected by the same variation in temperature (Canvin, 1965). All rules have exceptions, and the experiments of Appelqvist (1975) showed that different lines of zero-erucic acid rape could respond differently to the same climatic variations. 

However the activation of the A6 desaturation is shown later on. At 15 days it is very important. The apparent Km and Vm of the enz)mie are modified. This activation recovers the double bond index saturated acid ratio to 2.2 and is correlative to an increase of the triacylglycerol phosphatidyl choline ratio of the microsomes. Undoubtedly it is not correlative to the modification of the fatty acid composition of the membrane. Besides Ayala and Brenner have shown that the effect is not due to substrate deprivation (linoleate or a-linolenate) since rats fed on diets containing fish oil during 4 or 6 weeks have even lower A6 desaturation activity in liver microsomes than animals fed on sunflower seed oil compared to rats fed on EFA free diets (Table 2), Therefore the increase of the A6 desaturase activity in EFA deficiency is a physiological response of the cell to maintain the unsaturated/saturated acid ratio and fluidity of the membrane. 

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