Regioisomers of octanoic acid-containing structured triacylglycerols analyzed by tandem mass spectrometry using ammonia negative ion chemical ionization

Tandem mass spectrometry based on ammonia negative ion chemical ionization and sample introduction via direct exposure probe was applied to analysis of regioisomeric structures of octanoic acid containing structured triacylglycerols (TAG) of type MML, MLM, MLL, and LML (M, medium-chain fatty acid; L, long-chain fatty acid). Collision-induced dissociation of deprotonated parent TAG with argon was used to produce daughter ion spectra with appropriate fragmentation patterns for structure determination. Fatty acids constituting the TAG molecule were identified according to [RCO₂]⁻ ions in the daughter ion spectra. With the standard curve for ratios of [M-H-RCO₂H-100]⁻ ions corresponding to each [RCO₂]⁻ ion, determined with known mixtures of sn-1/3 and sn-2 regioisomers of structured TAG, it was possible to determine the proportions of different regioisomers in unknown samples. The method enabled quantification of MML- and MLM-type structured TAG. In the case of MLL- and LML-type TAG, it was possible to determine the most abundant regioisomer in the unknown mixture and estimate the proportions of regioisomers when there were more than 50% MLL-type isomers in the mixture.     

Effect of processing on the oxidative stability of low erucic acid turnip rapeseed (Brassica rapa) oil

The effect of various processing conditions on the composition and the oxidative stability of mechanically pressed (90–95°C) rapeseed oil was investigated. The five different rapeseed oils included crude (nondegummed), superdegummed, steam stripped (at 140°C for 4h, nondegummed), physically refined (degummed, bleached and deodorized at 240°C), and cold pressed (40°C) oils. Oils were autoxidized in the dark at 60°C and under light at 25°C. Oxidation was followed by measuring changes in the peroxide values (PV) and the consumption of tocopherol and carotenoid was measured. In the dark the oils reached PVs of 10 meq/kg in the order: cold pressed > superdegummed > steam stripped ≅ crude > refined. However, under light conditions the order changed as follows: cold pressed > crude ≅ steam stripped > superdegummed > refined. Processing had no effect on fatty acid composition nor α-tocopherol content of the oils. Superdegumming and steam stripping decreased the carotenoid content of the oils while cold pressing and refining reduced also chlorophyll, γ-tocopherol and phosphorus content of the oils.