Determination of totaltransfatty acids in foods: Comparison of capillary-column gas chromatography and single-bounce horizontal attenuated total reflection infrared spectroscopy

The totaltransfatty 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 column and by single-bounce horizontal attenuated total reflection spectroscopy (SB-HATR). Thetransfatty acid methyl esters (FAME) of 9-hexadecenoate (9t-16:1), 9-octadecenoate (9t-18:1), and 9,12-octadecadienoate (9t,12t-18:2) were identified by comparison of their retention times with those of known standards and quantitated. The isomersc,t- andt,c-18:2 were identified from their published retention times and included in the quantitation oftransFAME. Neat 50-µL portions of the FAME that were used for gas-chromatographic analysis also were analyzed by SB-HATR. This technique requires neither weighing nor quantitative dilution of test portions prior to spectroscopic quantitation of isolated double bonds oftransconfiguration. A symmetric 966-cm-1absorption band on a horizontal background was obtained from unhydrogenated soybean oil FAME as the reference material. For 9 of 11 products withtransfat content>5% of total fat, results obtained by SB-HATR were higher than those obtained by gas chromatography. Results obtained by the gaschromatographic procedure were slightly to significantly higher than those obtained by SB-HATR for the six foods in whichtransfat content was <5% of total fat.