Determination of the fatty acids and oil content of evening primrose ( Oenothera biennis L.)

Abstract

A rapid method for the analyses of oil content and individual fatty acids of evening primrose ( Oenothera biennis L.) is described. Oil was extracted from the seed with a Polytron probe generator using petroleum ether. A portion of the extract was concentrated to determine oil content. Results obtained with the Polytron extraction procedure were comparable to those obtained with a Soxhlet extraction procedure using the same solvent. Saponification of the oil with methanolic sodium hydroxide, methylation with methanolic sulfuric acid, and extraction of the esters with hexane was accomplished in a single reaction vial. Quantitation of the extracted esters was carried out by capillary gas chromatography. A number of fatty acids were identified by gas chromatographic-mass spectrometric studies of the extracted esters and methyl esters separated by their degree of unsaturation with silver nitrate-silicic acid chromatography. Saturated fatty acids from C 12 to C 24 were present in the oil with the even numbered acids present in the larger amounts. Eight monounsaturated fatty acids from C 14:1 to C 20:1 were identified with C 18:1 (n-9) as the major constituent of this fraction. Seven polyunsaturated fatty acids were identified with C 18:2 (n-6) and C 18:3 (n-6) as the major component. Analysis of seeds from different parts of evening primrose plants showed that differences in gamma-linolenic [C 18:3 (n-6)] acid and oil content exist due to location of the seed pods.