Spectroscopic characterisation of dimeric oxidation products of phytosterols

• Tentative chemical structures of dimers of phytosterols differing in polarity were proposed.
• Dimeric fractions were characterised by MS, NMR and IR spectroscopies.
• Disteryl ethers were identified as prominent dimers of thermo-oxidized β-sitosterol.

Sterol dimers are the main oxidation products formed during sterols degradation at elevated temperatures. An investigation was carried out to decipher the structure of dimers differing in polarity, formed during β-sitosterol thermo-oxidation. The oxidation products were fractionated using silica gel into non-polar (NP), mid-polar (MP) and polar fractions (P). Oligomers were further separated by size-exclusion chromatography (SEC). Tentative chemical structures of non-polar, mid-polar and polar dimers were identified using Ag+/CIS–MS and APCI–MS procedures after on-line RP-HPLC separation. Further structures were verified by NMR and FT-IR spectroscopies.