A simplified method for determining sn-2 fatty acid composition of triacylglycerol oils by UPLC-Q-TOF-MS

Abstract

Positional distribution of fatty acids determines the nutritional value of edible oils, and can be reflected by the sn-2 fatty acid composition. Traditional determination methods generally involve three steps: hydrolysis, separation, and gas chromatography analysis. The separation process is complex and consumes large amounts of organic solvents. To address this issue, we developed a separation-free method. In this approach, triacylglycerol oils were first hydrolyzed by a sn-1,3 regioselective lipase, which retains the first step of the traditional method. The fatty acids originally esterified at the sn-2 position are retained and form 2-monoacylglycerol, and the 2-monoacylglycerol composition has conventionally been considered as the sn-2 fatty acid composition. However, we also took into account that the majority of 1-monoacylglycerol in the hydrolysate actually originate from acyl migration of 2-monoacylglycerol. We propose that the fatty acid composition of monoacylglycerols in the hydrolysate directly represents the sn-2 fatty acid composition. A UPLC-Q-TOF-MS-based method for directly determining the composition of monoacylglycerols was developed, with mass spectrometry parameters and formic acid concentration in the mobile phase optimized, followed by method validation. Finally, the new method was applied to various triacylglycerol oils and compared with the traditional method to confirm its validity.