Session: Parallel session 9 - Complex mixtures - polymers - microplastics

How to improve the resolution of MS/MS based molecular networks? By adding the ion mobility dimension. A cocoa polyphenol metabolomics based study.

Introduction:

During processing (i.e. fermentation, sun drying...), the polyphenols from cocoa beans form complex isomeric compounds that co-elute in liquid chromatography. MS/MS spectra correspond to mean fragment ion spectra and are poorly informative. A feature-based molecular networking (FBMN) analysis reveals large clusters containing tenth of compounds. To improve the resolution of the FBMN we generated trapped ion mobility spectrometry (TIMS) data in a UHPLC-HRMS/MS workflow.



Methods:

Two sets of fine cocoa beans, having the particularity to generate chocolates of dark black or light brown colours [1], were analysed on a UHPLC-TIMS-QTOF mass spectrometer, with and without activation of the ion mobility module. The processed HRMS and HRMS/MS data underwent univariate and multivariate statistical analyses as well as FBMN analysis.



Results:

Thanks to the additional mobility dimension, we generated additional nodes and clusters in the FBMN, corresponding to position isomers or stereoisomers with different MS/MS fragmentation patterns. They included polyphenol monomers ((epi)catechin-O-hexoside and (epi)catechin-C-hexoside), dimers (B-type procyanidin dimers and dehydrodicatechins B), trimers (B-type procyanidin trimers and dehydrotricatechins B), and tetramers (B-type procyanidin tetramers). A metabolomics statistical analysis workflow revealed that the majority of those isomers were discriminating compounds on cocoa beans, for black or brown chocolate. Dehydrodi(or tri)catechins B are oxidation products formed during cocoa bean fermentation, while their corresponding isomers, B-type procyanidin di(or tri)mers, are native secondary metabolites.



Novel aspects:

An IMS based method to enhance the resolution of molecular networks of isomeric plant specialized metabolites.



[1] Shades of Fine Dark Chocolate Colors: Polyphenol Metabolomics and Molecular Networking to Enlighten the Brown from the Black

Metabolites, 2023, https://doi.org/10.3390/metabo13050667