Comprehensive characterization of C-glycosyl flavones in wheat (Triticum aestivum L.) germ using UPLC-PDA-ESI/HRMSn and mass defect filtering.

A comprehensive characterization of C-glycosyl flavones in wheat germ has been conducted using multi-stage high resolution mass spectrometry (HRMSn ) in combination with a mass defect filtering (MDF) technique. MDF performed the initial search of raw data with defined C-glycosyl flavone mass windows and mass defect windows to generate the noise-reduced data focusing on targeted flavonoids. The high specificity of the exact mass measurement permits the unambiguous discrimination of acyl groups (nominal masses of 146, 162 and 176.) from sugar moieties (rhamnose, glucose or galactose and glucuronic acid). A total of 72 flavone C-glycosyl derivatives, including 2 mono-C-glycosides, 34 di-C-glycosides, 15 tri-glycosides, 14 acyl di-C-glycosides and 7 acyl tri-glycosides, were characterized in wheat germ, some of which were considered to be important marker compounds for differentiation of whole grain and refined wheat products. The 7 acylated mono-O-glycosyl-di-C-glycosyl flavones and some acylated di-C-glycosyl flavones are reported in wheat for the first time. The frequent occurrence of numerous isomers is a remarkable feature of wheat germ flavones. Both UV and mass spectra are needed to maximize the structure information obtained for data interpretation.