New polyphenolic compounds in commercial deodistillate and rapeseed oils

Different phenolic compounds were identified in commercial rapeseed oils, as well as in a commercial by-product of oil refining, the deodistillate. Reversed-phase HPLC analysis and the successive fragmentation procedure by ESI-MSⁿ (electrospray ionisation mass spectrometry) showed a significant fragmentation pattern for new compounds, the cis- and trans-diastereomers of 4-vinylsyringol dimer [cis-4,6-dimethoxy-5-hydroxy-1-methyl-3-(3′,5′-dimethoxy-4′-hydroxyphenyl)indane and trans-4,6-dimethoxy-5-hydroxy-1-methyl-3-(3′,5′-dimethoxy-4′-hydroxyphenyl)indane] and the vinylsyringol trimer in trace amounts. The phenylindane were isolated by preparative HPLC and was clearly identified by nuclear magnetic resonance spectroscopy. Besides sinapic acid and its decarboxylated derivative, 4-vinylsyringol, this newly identified 4-vinylsyringol dimer was present in the deodistillate of processed rapeseed oil in significant amounts (sinapic acid, approx. 500 mg/kg, 4-vinylsyringol, approx. 200 mg/kg and 4-vinylsyringol dimer, approx. 3.50 g/kg). Additionally, the phenylindane was also detected in small amounts (6.4–63.0 mg/kg or trace amounts, respectively) in commercial rapeseed oils. The newly identified phenylindane compound had a high antioxidative potential (3.9 trolox-eq.) and might be an important phenolic compound in commercial deodistillate and rapeseed oils.