Untargeted metabolomics study of Lonicerae japonicae flos processed with different drying methods via GC-MS and UHPLC-HRMS in combination with chemometrics

The medicinal values and economic benefits of Lonicerae japonicae flos are directly affect by the post-harvest processing due to the organoleptic and chemical properties. To explore the differences of Lonicerae japonicae flos obtained by various drying methods, untargeted metabolomics combined with chemometrics was first used to investigate the metabolite differences among them. The metabolomics analysis was accomplished by introducing automatic data analysis tools, i.e., autoGCMSDataAnal and AntDAS, which developed for gas chromatography-mass spectrometry (GC-MS) data analysis and ultrahigh performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) data analysis, respectively. The results indicated that about 66 volatile compounds were screened and identified by autoGCMSDataAnal coupled with GC-MS, among which 29 compounds were confirmed qualitatively by standards. Meanwhile, 30 nonvolatile compounds were screened and identified by AntDAS combined with UHPLC-HRMS and 16 compounds were confirmed qualitatively by standards. In particular, most of polyphenols including rutin, cynaroside, isoquercetrin, chlorogenic acid etc., had their maximum content at the freeze drying and minimum at the shade drying. Finally, partial least squares discrimination analysis (PLS-DA), hierarchical clustering analysis (HCA) and heat map analysis were used for discriminating samples from various processing methods. Relative high-quality samples with good appearance characteristics could be obtained by freeze drying, heat-pump drying and hot air drying. Moreover, the antioxidant components were well preserved under freeze drying. The differences of primary and secondary metabolites in Lonicerae japonicae flos obtained with diverse drying methods were revealed, which could be helpful to determine the optimal drying method according to specific request.