Influence of milk fat presence on the determination of trans fatty acids in fats used for infant formulae

The analysis of the trans fatty acids (TFAs) isomer distribution by gas chromatography with flame ionisation detection (GC-FID) has been proposed to assess the quality of the vegetable oils used in infant formula. Depending on the deodorisation temperature reached during refining, TFA content may vary considerably. On the other hand, TFAs occur naturally in milk and therefore, are present in infant formulae containing milk fractions. We demonstrate that to unambiguously check the quality of vegetable fat used in infant formulae only one trans isomer of C 18:3 (C18:3c9,c12,t15) may be used as a marker of vegetable fat presence. In the GC-FID chromatograms, the region of C 18:2, eluted on a CP-Sil 88 capillary column between 31.8 and 33.2 min, is interfered with the presence of milk fat TFA isomers. When no milk fat is present both regions of TFA of C 18:2 and C 18:3 may be used. Milk fat samples from Europe, Brazil and Indonesia, collected during different seasons showed a variation of total TFA isomers of C18:2 in the range of 0.20-0.80g/100g total fatty acids. On the other hand, total conjugated C18:2 (c9,t11 or CLA) ranged from 0.33 to 1.37g/100g total fatty acids in all the analysed samples. The presented data may contribute to evaluate the nutritional impact of milk fat TFA in infant formulae. (C) 2002 Elsevier Science B.V. All rights reserved.