Comprehensive characterization of naturally occurring antioxidants from the twigs of mulberry ( Morus alba ) using on‐line high‐performance liquid chromatography coupled with chemical detection and high‐resolution mass spectrometry

INTRODUCTION: The mulberry tree ( Morus alba L.) is a prolific source of biologically active compounds. There is considerable growing interest in probing M. alba twigs as a source of disruptive antioxidant lead candidates for cosmetic skin care product development. OBJECTIVE: An integrated approach using high‐performance liquid chromatography (HPLC) coupled with either chemical detection (CD) or high‐resolution mass spectrometry (HRMS) was applied to the hydroalcoholic extract of M. alba to detect and identify lead antioxidant compounds, respectively. MATERIAL AND METHODS: The twigs were weighed, powdered and homogenized using a mill and the extract was prepared using 70% aqueous ethanol. The antioxidant metabolites were detected with HPLC coupled with CD (based on the ORAC assay) and their structural identification was carried out using a Q‐Exactive Orbitrap MS instrument. RESULTS: Using this approach, 13 peaks were detected as overall contributors to the antioxidant activity of M. alba , i.e. mulberrosides (A & E), oxyresveratrol & its derivatives, moracin & its derivatives and a dihydroxy‐octadecadienoic acid, which together accounted for >90% of the antioxidant activity, highlighting the effectiveness of the integrated approach based on HPLC‐CD and HPLC‐HRMS. Additionally, a (3,4‐dimethoxyphenyl‐1‐O‐β‐D‐apiofuranosyl‐(1″ → 6′)‐O‐β‐D‐glucopyranoside was also discovered for the first time from the twig extract and is presented here. CONCLUSION: To our knowledge, this is the first report from M. alba twigs using HPLC‐CD and HPLC‐HRMS that identifies key compounds responsible for the antioxidant property of this native Chinese medicinal plant.