Comparative study on phytosterol oxidation products determination in high oleic sunflower oil by using cholesterol oxidation products or purified phytosterol oxidation products as reference materials

Phytosterols received great interest over the last decade due to their capacity to compete with cholesterol absorption during digestion. However, phytosterols can be oxidized resulting in oxidation products (phytosterol oxidation products, POPs), which could be associated with negative effects on human health. Thus, different studies were focused on their determination in foods and biological systems. Since no POPs commercial standards are available, except for 7-ketositosterol, the cholesterol oxidation products (COPs) are often used as reference material (RM) for analytical purposes. However, up to date, no data confirmed the suitability of that approach. In the present study, two different laboratories were enrolled, and commercial standard COPs with pure isolated POPs, obtained by a validated semi-preparative HPLC method, were compared to determine the content of POPs in refined high oleic sunflower oil. Two technologies were also considered LC-Orbitrap-HRMS (LC-MS) and GC-MS. Except for 7-keto derivatives, the use of COPs as RM led to an overestimation of the POPs content by both tested systems LC-MS and GC-MS. Again, the Orbitrap technique was more sensitive than GC-MS, and significant differences (p<0.05) in the quantitation were also found between LC-MS and GC-MS when identical stock solutions were used. The results demonstrated that the analysis of POPs is challenging, and the use of pure POPs leads to reduce the risk of a poor determination of POPs in vegetable oils and the use of COPs as RM for detecting and quantifying POPs should be reconsidered.