Application of standard addition to eliminate conjugated linoleic acid and other interferences in the determination of total Trans fatty acids in selected food products by infrared spectroscopy

Abstract

AbstractA novel and rapid (5 min) attenuated total reflection‐Fourier transform infrared (ATR‐FTIR) spectroscopic method AOCS Cd 14d‐99 for the determination of total isolated trans fatty afids, which absorb at 966 cm‐, was recently developed, collaboratively studied, and applied to food products containing 1–50% rans fat (as percentage of total fat). Attempts to apply the ATR‐FTIR method to biological matrices of low trans fat and/or low total fat content, and to dairy and other products were not satisfactory due to interfering IR absorptions in the trans region. One group of interfering compounds with absorption bands near 985 and 948 cm−1 was the cis/trans positional isomes of conjugated linoleic acid (CLA) found in dairy and meat products from ruminants at levels of <1% (as percentage of total fat). In the present study, we modified the ATR‐FTIR method to overcome matrix interferences. This modification, which consisted of applying the standard addition technique to the ATR‐FTIR determination, was also applied to several food products, namely, dairy products, infant formula and salad oil dressing, which successfully eliminated interfering absorbances that impacted on accuracy. The presence of <1% CLA in two butter and two cheese products containing 6.8, 7.5, 8.5, and 10.4% trans fatty acids (as a percentage of total fat) would have led to errors of −11.6, 10.4, 17.6 and 34.6%, respectively, in trans fat measurements had the standard addition technique not been used. The applicability of ATR‐FTIR to the quantitation of food products is discussed.