4-O-Caffeoylquinic acid as an antioxidant marker for mulberry leaves rich in phenolic compounds

Jerome G. Ganzon ^a, Lih-Geeng Chen ^b, Ching-Chiung Wang ^a,*

^a School of Pharmacy, College of Pharmacy, Taipei Medical University, 250 Wu-Hsing Street, Taipei 110, Taiwan, ROC

^b Department of Microbiology, Immunology and Biopharmaceuticals, College of Life Sciences, National Chiayi University, 300 University Road, Chiayi 600, Taiwan, ROC

Mulberry (Morus alba L.) leaves are widely used as herbal tea to prevent heat stroke. Potential chemical markers of the antioxidant properties and its correlation with harvesting times and leaf location were explored in this study. A 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay guided isolation of mulberry leaves extract provided five phenolic compounds: 5-O-caffeoylquinic acid (1), 4-O-caffeoylquinic acid (2), gastrodin (3), isoquercetin (4) and rutin (5). The 50% radical-scavenging concentrations (SC50) of these compounds were 32.76 ± 0.27, 11.41 ± 0.48, 404.30 ± 4.92, 10.63 ± 0.96, and 10.57 ± 0.61 mg/mL, respectively. Chromatographic fingerprinting allowed content analysis of 1-5 in samples over a 12-month period. Compounds 1-5 were abundance in apical leaves (0-10 cm) in January and February at temperatures < 20 C. Contents of 2 and 5 were highest in these months and were strongly correlated to the antioxidant property. Therefore, we suggested that the mulberry leaves harvested during January and February have high yield of 4-O-caffeoylquinic acid and this compound can be used as antioxidative marker in mulberry leaves.

Keywords: Morus alba, Leaves location, Antioxidant, 4-O-Caffeoylquinic acid, Harvest time