An integrated study of quality variations for Eucommia ulmoides Oliver staminate flower processed with different drying treatments by untargeted metabolomics coupled with chemometrics

Eucommia ulmoides Oliver staminate flower (EUF) has been increasingly served as a potential feedstock for nutraceuticals. An integrated approach of untargeted metabolomics based on gas chromatography hyphenated with mass spectrometry (GC-MS) and ultrahigh performance liquid chromatography hyphenated with high resolution mass spectrometry (UHPLC-HRMS) coupled with advanced chemometric method was applied to investigate the metabolic variations of EUF obtained from various drying treatments. The metabolomics analysis was conducted automatically in our newly developed data analysis platform AntDAS. Chemometric methods were further used to provide additional insight into the chemical differences of EUF. 34 volatile and semi-volatile as well as 89 nonvolatile compounds were identified and demonstrated significant differences among diverse drying treatments. Moreover, among which 27 volatile and semi-volatile compounds along with 35 nonvolatile compounds were verified qualitatively by standards. The results revealed that shade drying was more effective for the preservation of volatile and semi-volatile substances, including sugars and vitamins. Freeze drying was conducive for preserving nonvolatile compounds, such as iridoids, flavonoids, and organic acids. The content of alcohols, amino acids, and nucleosides was abundant in heat-pump drying, oven drying, and hot air drying, respectively. In addition, hot air, heat pump, and oven drying methods showed a moderate level of the majority of bioactive components and suitable for industrialization process. This work potentially highlights the possibility of using chemometrics in conjunction with untargeted GC-MS and UHPLC-HRMS analysis for quality assessment of EUF.