The Mechanism Of The Flavor Reversion Of Soybean Oil

In this study, non-added antioxidant soybean oil was the research object. Non-added antioxidant soybean oil was kept at 60℃ in the dark for a period of time in order to imitate oxidation at room temperature. Through the analysis of different periods samples to identify the initial time of generating reversion flavor. In order to further study what types of components in the lipid promoting oxidation resulted in reversion flavor of soybean oil, the soybean oil was separated step by step by column chromatography, and then detected by stick thin layer chromatography. The separated parts were added to the soybean oil triglycerides, and then placed at 60℃ for the period determined. Sensory evaluation, PV, volatile and non-volatile compounds and metal ions detected were used to evaluate the flavor reversion of soybean oil. The mechanism of the flavor reversion of soybean oil was suggested.Eventually oxidation for 31 hours kept at 60℃ has been determined as the initial time of generating reversion flavor, which was confirmed by PV, sensory evaluation and volatile compounds analysis by Gas chromatography coupled with mass spectrometry (HS-SPME-GC-MS). The soybean oil 1.5 ± 0.001g was separated step by step by column chromatography.The column was eluted stepwise with a diethyl ether/n-hexane mixture system:ⅰ) n-hexane/diethyl ether (87:13), ⅱ) (75:25), ⅲ) (50:50), ⅳ ) (0:100), and ⅳⅴ ) methanol. It was identified by stick thin layer chromatography, showing good separation. Finally the fractionated component eluted by methanol is supposed to play a significant role in promoting oxidation of soybean oil TAG determined by PV, sensory evaluation and analysis of GC-MS. Peroxide value of the methanol sample was 3.04mmol/kg. Meanwhile, 52 volatile compounds have been detected by headspace-solid phase microextraction Gas chromatography coupled with mass spectrometry (HS-SPME-GC-MS) method, which contained 5 alcohols,9 aldehydes, and 38 other compounds. The nonvolatile compounds were core aldehydes(ALD), contained 9-oxononanoyl-,12-oxo-9,10-epoxydodecenoyl-, and 13-oxo-9,11-tridecadienoyl-containing acylglycerols. In addition,5.63ppb and 76.8ppb of copper and iron were detected from the eluted fraction of methanol by ICP-MS. Through the mass spectrometry detection, the major composition of the methanol elution part turns out to be lecithin.Under the catalysis of lecithin and metal ions, soybean oil has undergone internal cracking and oxidation, and eventually produced reversion flavor. Reversion flavor is related with the amount of the 2-Pentyl-furan,2-Octenal,(E),2-Heptenal,(E) and 6-Nonenal(z) generating.