Wild helianthus annuus, a potential source of reduced palmitic and stearic fatty acids in sunflower oil

Abstract

The current trend in human diets is to decrease consumption of the saturated palmitic and stearic fatty acids. Healthy diets restricting not only total fat, but the saturated portion of that fat, would decrease blood serum cholesterol and the risk of coronary heart diseases. Edible vegetable oils are the principal source of fats in many diets. Sunflower oil, which is fifth in production among edible vegetable oils in the world, contains 65 g kg-1 saturated palmitic and 45 g kg-1 saturated stearic acids. These concentrations are high compared to rapeseed oil with 40 g kg-1 palmitic and 20 g kg-1 stearic acids. A reduction of saturated fats in traditional sunflower oil would lead to a healthier edible oil. The objective of this preliminary study was to search the vast genetic diversity available from wild Helianthus annuus, the closest relative of the cultivated sunflower, for potential sources of reduced saturated fatty acids; less than 70 g kg-1 combined palmitic and stearic fatty acids. Achenes of eighty-two populations of wild H. annuus were collected from the central Great Plains of the USA. Composited 20-achene samples from each population were analyzed for saturated fatty acids using organic base-catalyzed transesterification of fatty acid methyl esters and capillary gas chromatography. The average palmitic acid concentration ranged from 39 to 65 g kg-1 for the populations. Average stearic acid concentrations ranged from 19 to 37 g kg-1. Achene oil of one population of wild H. annuus from Holmquist, South Dakota, USA had a palmitic acid concentration averaging 39 g kg-1, while stearic acid averaged 19 g kg-1. The combined 58 g kg-1 palmitic and stearic acids is almost 50% lower than the present level of these fatty acids in sunflower oil. The level of saturated fatty acids observed in the population remained low when plants were grown in the greenhouse under uniform conditions. In the greenhouse palmitic acid concentration of this population averaged 40 g kg-1, while stearic acid averaged 19 g kg-1. Crosses between this population and an inbred cultivated line produced F1 plants with an achene oil that averaged 39 g kg-1 palmitic and 21 g kg-1 stearic acid. In comparison, the inbred cultivated parent averaged 61 g kg-1 palmitic and 51 g kg-1 stearic acid. F2 plants produced achene oil that averaged 45 g kg-1 palmitic and 23 g kg-1 stearic acid, for a total of 68 g kg-1. When F1 plants were backcrossed to the cultivated inbred, BC1F1 plants produced an achene oil that averaged 45 g kg-1 palmitic and 26 g kg-1 stearic acid for a total of 71 g kg-1. In comparison, the inbred cultivated parent averaged 65 g kg-1 palmitic and 42 g kg-1 stearic acid, for a total of 107 g kg-1. Preliminary information indicates that palmitic and stearic fatty acids in sunflower oil can be reduced by introducing genes from a wild annual population into cultivated sunflower. Further research will be needed to determine the inheritance of these fatty acids. Other agronomic traits will also have to be monitored during introgression of the fatty acids genes.