Identification of quinoline, carboline and glycinamide compounds in cow milk using HRMS and NMR

The aim of this work was to characterise new UV-absorbing compounds (UAC) in cow milk in order to gain an overview of the molecular diversity of the minor bioactive constituents, that could be used to trace animal feed or that potentially affect milk quality. UAC were extracted from lyophilized milks, partitioned using SPE C-18 cartridges, purified by semi-preparative HPLC then analysed by HPLC/DAD/HRMS in both ESI− and ESI+ ionisation mode. Compounds that remained unidentified after comparison with UV and MS databases were analysed by 1D and 2D NMR techniques. The identification and structural elucidation of N-cinnamoylglycine, 2,4-, 2,6-, 2,8-quinolinediols, and 1-methyl-3-carboxy-beta-carboline are described.