Analysis of sterols from various food matrices

Two methods suitable for routine phytostanol/phytosterol analysis of various sterol-enriched food matrices and phytostanyl/phytosteryl fatty acid ester ingredients are introduced. A method based on hot saponification of a sample with ethanolic potassium hydroxide in the presence of an internal standard (5β-cholestan-3α-ol) is adequate for most matrices, such as spread, milk and yoghurt. Some matrices, like pasta, require acid hydrolysis in order to release matrix-incorporated bound sterols or sterols from steryl glycosides before the saponification step. After saponification, the unsaponifiable material containing phytostanols and phytosterols is extracted into an organic solvent (e.g. heptane), followed by evaporation of the solvent to dryness. Sterols are separated as their trimethylsilyl ether derivatives with a gas-liquid chromatograph (GC), on a column coated with 5% phenyl/95% dimethylpolysiloxane, and detected with a flame ionization detector. The GC conditions applied provide efficient separation of the most abundant phytostanols/phytosterols in 15 min, a wide linear range of stanols/sterols without the need of defining sterol response factors. The methods are repeatable and accurate, as shown with standard addition trials. These methods were applied to determine phytostanol/phytosterol contents of several sterol-enriched functional food products, and the analyzed amounts were in good accordance with the information provided on the packaging labels.