DETERMINATION OF TOTAL TRANS-FATTY-ACIDS IN FOODS - COMPARISON OF CAPILLARY-COLUMN GAS-CHROMATOGRAPHY AND SINGLE-BOUNCE HORIZONTAL ATTENUATED TOTAL-REFLECTION INFRARED-SPECTROSCOPY

The total trans fatty acid content of 18 food products was determined, after acid hydrolysis, extraction and methylation of fatty acids, by gas chromatography with a polar 100% cyanopropylsiloxane capillary col umn and by single-bounce horizontal attenuated total reflection spectr oscopy (SB-HATR). The trans fatty acid methyl esters (FAME) of 9-hexad ecenoate (9t-16:1), 9-octadecenoate (9t-18:1), and 9,12-octadecadienoa te (9t, 12t-18:2) were identified by comparison of their retention tim es with those of known standards and quantitated. The isomers c,t- and t,c-18:2 were identified from their published retention times and inc luded in the quantitation of trans FAME. Neat 50-mu L portions of the FAME that were used for gas-chromatographic analysis also were analyze d by SB-HATR. This technique requires neither weighing nor quantitativ e dilution of test portions prior to spectroscopic quantitation of iso lated double bonds of trans configuration. A symmetric 966-cm(-1) abso rption band on a horizontal background was obtained from unhydrogenate d soybean oil FAME as the reference material. For 9 of 11 products wit h trans fat content >5% of total fat, results obtained by SB-HATR were higher than those obtained by gas chromatography. Results obtained by the gas-chromatographic procedure were slightly to significantly high er than those obtained by SB-HATR for the six foods in which trans fat content was <5% of total fat.