|
Abstract
|
In this study, a simple and reliable method based on the dispersive magnetic solid phase extraction (DMSPE) with modified magnetic nanoparticle followed by gas chromatography-mass spectrometry (GC-MS) has been developed for determination of sterol composition in liquid milk samples and detection of palm oil in milk fat. The hydrophobic magnetic nanoparticles were synthesised by assembling octadecyltrimethoxysilane (ODTMS) onto the iron magnetic nanoparticles and used as adsorbent for DMSPE. The method is based on the saponification of milk fats followed by extraction of unsaponificated sterols by DMSPE procedure and subsequent desorption of sterols into acetonitrile for GC-MASS analysis. The mass fraction of each sterol, as percentage of the total sterol content, was used for quantitative determination of sterols in milk samples. The main factors affecting extraction efficiency, including extraction and desorption time, desorption conditions, sample volume, amount of magnetic adsorbent and saponification conditions, were investigated. The results of this study showed that addition of palm oil to milk caused substantial changes in sterols contents and fractions of phytosterols (β-sitosterol, stigmasterol and compesterol) increased with increasing the addition level of palm oil. Based on the evidence for the presence of vegetable sterols in pure milk fat, a limit of detectability of 3% for palm oil was obtained in milk fat. Under the optimum conditions, the inter-day precision and intra-day precision for sterols of sample containing 3% fat (10% of the fat containing palm oil) were in the range of 1.1-1.8% and 1.3-1.9%, respectively. Also, the good recovery of the total phytosterol (97-97.2%) showed that purposed method can be successfully applied to the determination of phytosterols in milk samples for detection of palm oil addition.
|