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

Mulberry (Morus alba L.) leaves are widely used as herbal tea to prevent heat stroke. Potentialchemical markers of the antioxidant properties and its correlation with harvestingtimes 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 phenoliccompounds: 5-O-caffeoylquinic acid (1), 4-O-caffeoylquinic acid (2), gastrodin (3), isoquercetin(4) and rutin (5). The 50% radical-scavenging concentrations (SC50) of thesecompounds 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 1e5 insamples over a 12-month period. Compounds 1e5 were abundance in apical leaves (0e10 cm) in January and February at temperatures < 20 _C. Contents of 2 and 5 were highestin these months and were strongly correlated to the antioxidant property. Therefore, wesuggested that the mulberry leaves harvested during January and February have high yieldof 4-O-caffeoylquinic acid and this compound can be used as antioxidative marker inmulberry leaves.