Capillary gas chromatographic analysis of complex phytosteryl/-stanyl ester mixtures in enriched skimmed milk-drinking yoghurts

The capillary gas chromatographic (GC) separation of complex mixtures of plant steryl and stanyl fatty acid esters was achieved using a medium polar trifluoropropylmethyl polysiloxane as stationary phase. An approach allowing the facile synthesis of steryl/stanyl fatty acid esters was developed, thus creating the basis for a calibration of the method for the different types of ester mixtures to be expected in enriched foods. The usefulness of the approach for the rapid authentication of enriched low-fat products via qualitative and quantitative analysis of intact steryl and stanyl fatty acid esters was demonstrated by analysis of two skimmed milk-drinking yoghurts commercially available on the European market. Combining the extraction of lipids under acidic conditions with the GC separation step showed that one of the products contained a steryl/stanyl ester mixture obtained from long-chain sunflower oil fatty acids and sterols/stanols from tall oil. The other product, however, was shown to contain the rather unusual steryl/stanyl esters of the medium-chain octanoic and decanoic acid as ingredients.