Occurrence of mixtures of geometrical isomers of conjugated octadecatrienoic acids in some seed oils: Analysis by open‐tubular gas liquid chromatography and high performance liquid chromatography

Abstract

Abstract Analytical methods to obtain the detailed compositions of the fatty acids in oils containing more than one conjugated octadecatrienoic acid by open‐tubular gas liquid chromatography (GLC) and by reversed‐phase high performance liquid chromatography (HPLC) were established. Effective GLC separations of cis,trans,trans ‐9,11,13‐octadecatrienoic acid ( ctt ‐9,11,13–18∶3), ctc ‐9,11,13–18∶3, ttc ‐9,11,13–18∶3, ttt ‐9,11,13–18∶3, ttc ‐8,10,12–18∶3, and ttt ‐8,10,12–18∶3 were obtained with an opentubular column coated with the nonpolar liquid phase OV‐1 using an instrument having all‐glass carrier gas pathways. The HPLC method also gave satisfactory separations for the isomeric conjugated octadecatrienoates on the basis of number of the cis and trans double bonds. Two or three minor conjugated trienoic acids were found along with the principal conjugated trienoic acid in tung oil, and seed oils of cherry, Prunus sp., Momordica charantia, Trichosanthes anguina, Punica granatum, Catalpa ovata , and Calendula officinalis . The mechanism for the formation of the conjugated trienoic acid mixtures in the seed oils is discussed. The C. ovata seed oil also contained ct and tt ‐9,12‐octadecadienoic acids. The tt isomer is presumed to be a precursor of ttc ‐9,11,13–18∶3, the main conjugated trienoic acid in this oil.