Optimization of analytical procedures for GC–MS determination of phytosterols and phytostanols in enriched milk and yoghurt

The aim of the present study is to contribute to a correct determination of vegetal sterol and stanols found in enriched milks and yogurts, used as functional foods, using GC–MS. The optimization of the method, specially the saponification step, as well as the corresponding analytical validation, is the main goal of this study. Saponification temperatures and times that gave the best results were 80 °C/45 min for milk, and 60 °C/90 min for yoghurt samples. KOH concentration solutions of 2.0 and 2.5 M were selected as the best saponification reagents for milk and yoghurt, respectively. It was also verified that volumes of 1500 μl and 2500 μl KOH were enough to react with 250 μl of milk and 100 μl of yoghurt. Accuracy, repeatability and intermediate precision of the method were calculated at 89.2% and 91.5%, 6.0% and 4.45%, 11.8% and 9.4%, for milk and yoghurt, respectively, while the limit of detection was determinate at 0.1 μg/ml for both matrices.