No abstract

A mixture of phytosterols/-stanols, consisting of 75% β-sitosterol, 12% sitostanol, 10% campesterol, 2% campestanol, and 1% others, was esterified with linoleic acid. The resulting mixture of phytosteryl/-stanyl linoleates was subjected to thermal oxidation at 180 °C for 40 min. A silica solid-phase extraction was applied to separate a fraction containing the nonoxidized linoleates and nonpolar degradation products (heptanoates, octanoates) from polar oxidation products (oxo- and hydroxyalkanoates). In total, 15 sitosteryl, sitostanyl, and campesteryl esters, resulting from oxidation of the acyl chain, could be identified by GC-FID/MS. Synthetic routes were described for authentic reference compounds of phytosteryl/-stanyl 7-hydroxyheptanoates, 8-hydroxyoctanoates, 7-oxoheptanoates, 8-oxooctanoates, and 9-oxononanoates, which were characterized by GC-MS and two-dimensional NMR spectroscopy. The study provides data on the formation and identities of previously unreported classes of acyl chain oxidation products upon thermal treatment of phytosteryl/-stanyl fatty acid esters.

A GC-based approach involving preseparation via solid-phase extraction was established for the quantitation of acyl chain oxidation products (ACOPs) formed upon thermo-oxidation (180 °C, 40 min) of oleates and linoleates of phytostanols and phytosterols. The concentrations of ACOPs resulting from initially formed 9-hydroperoxides (octanoates, 8-hydroxyoctanoates, 9-oxononanoates) were higher than those from 8-hydroperoxides (heptanoates, 7-hydroxy- and 7-oxoheptanoates, 8-oxooctanoates) in both oleates and linoleates. Significantly higher amounts of ACOPs were found in heat-treated linoleates compared to oleates. However, despite lower thermally induced losses of stanyl oleates and linoleates compared to the respective steryl esters, higher concentrations of ACOPs (approximately 9 and 10% of the ester losses, respectively) were observed in the heat-treated stanyl esters. In contrast, in the heated steryl oleates and linoleates the contribution of the ACOPs to the ester losses was lower (approximately 3 and 5%, respectively), and there was a more pronounced formation of oxidation products of the sterol moieties (approximately 26 and 18% of the ester losses, respectively).