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.