Discovering the\nEllagitannin Landscape of Dried Walnut\nShells by Liquid Chromatography with Tandem Mass Spectrometry

Walnut shells, often discarded as waste, hold hidden\npotential\nas a source of ellagitannins (ETs), compounds known for their promising\nantioxidant properties and health benefits. This study employed reversed-phase\nliquid chromatography (RPLC) coupled with Orbitrap-based high-resolution\nmass spectrometry (HRMS) via electrospray ionization (ESI) in negative\npolarity to investigate the ET profile in extracts of dried powdered\nwalnut shells. Several compounds belonging to various ET families\nwere successfully identified as deprotonated molecules ([M –\nH]<sup>−</sup>) and characterized, including mono-, di-, tri-,\ntetra-, and pentagalloyl glucopyranoses, as well as ETs containing\nthe hexahydroxydiphenoyl (HHDP) group. Characteristic product ions\nwere identified in HR tandem MS spectra and employed to recognize\nthe ET landscape. Analysis revealed a complex picture with more than\n10 isomers identified in some cases. However, the structural similarity\nand limitations in MS/MS data hindered the definitive identification\nof all isomers. Characterization of ETs featuring HHDP groups also\nremained challenging. Despite these restraints, the estimated total\ncontent of ETs suggests potential application in the food, pharmaceutical,\nand cosmetic industries of those extracts. These findings indicate\nthat walnut shells can be considered a sustainable source of health-promoting\ncompounds, contributing to a greener economy.