Food glycomics: Dealing with unexpected degradation of oligosaccharides during sample preparation and analysis

This study reveals that unexpected degradation of food oligosaccharides can occur during conventional glycomics workflows, including sample preparation and analysis by liquid chromatography-mass spectrometry (LC-MS). With the present investigation, we aim to alert the scientific community of the susceptibility of specific glycosidic linkages to degradation induced by heat and acid. Key standard oligosaccharides representing the major types found in foods (3'-sialyllactose and 6'-sialyl-N-acetyllactosamine for milk, raffinose and stachyose for legumes) were selected as model systems and underwent each of the following treatments independently: (1) labeled with the derivatizing agent 1-aminopyrene-3,6,8-trisulfonic (APTS) (followed by analysis with a capillary electrophoresis system coupled with a fluorescence detector), (2) dried from an acetonitrile-water mixture containing 0.1% trifluoroacetic acid, and (3) injected into an LC-MS system. We demonstrated that both raffinose and stachyose degraded during APTS-labeling by the acid in the labeling reagents. We also discovered that during centrifugal evaporation at 37 °C, all of the four nonderivatized oligosaccharides tested were partially degraded. Additionally, when the LC-MS eluent contained 0.1% formic acid, 3'-sialyllactose, raffinose, and stachyose underwent extensive in-source fragmentation during analysis. Lastly, we identified a simple strategy that can reduce the probability of incorrect oligosaccharide identification resulting from extensive in-source fragmentation.