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

Abstract

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.

Abstract

The genus Morus consists of over 150 species belonging to the Moraceae family and among them, the Mulberry tree (e.g. Morus alba L.) continues to be a prolific source of biologically active compounds. The hydroalcoholic extract of the twigs was investigated with the aim to identify potential new antioxidant compounds which could be promising candidates for the development of cosmetic skin care product. An integrated approach using HPLC coupled with chemical detection (CD) and high resolution mass spectrometry (HRMS) was applied to detect and identify the antioxidant metabolites, respectively. Using this approach, 13 peaks were detected as contributors of the antioxidant activity. Eleven peaks were assigned to the known metabolites, namely, the Mulberosides (A and E), Oxyresveratrol derivatives, Moracin and its derivatives and a dihydroxy‐octadecadienoic acid derivative. These peaks contributed for41%, 9%, 17% and 20% of the antioxidant activity of the twig extract, respectively. Also, a new compound namely, 3,4‐dimethoxyphenyl‐1‐O‐β‐D‐apiofuranosyl‐(1’’→6’)‐O‐β‐D‐glucopyranoside was proposed and found to be responsible for 2% of the antioxidant activity. To our knowledge, this is the first report from Morus Alba twigs using HPLC‐CD and HPLC‐HRMS methodology that identifies key compounds responsible to the antioxidant property of this native Chinese medicinal plant.