Antioxidant activities of leaf extract of Salvia miltiorrhiza Bunge and related phenolic constituents

Leaf of Salvia miltiorrhiza Bunge, the waste part during the root harvest, is rich in health-promoting phenolics and is a novel resource of natural antioxidants. The acetone and methanol extracts of leaves (AL and ML, respectively) of S. miltiorrhiza were evaluated by various in vitro antioxidant assays. The total phenolic contents of AL and ML were 39.0 ± 1.13 and 54.3 ± 1.1 mg gallic acid equivalents/g extract tested, respectively. EC50 of ML was 7.0 ± 0.28 μg/mL in DPPH radical scavenging assay and 246.5 ± 10.35 μg/mL in superoxide radical quenching assay. It was also found that ML has prominent effects on the inhibition of linoleic acid oxidation (93.2%), which was equivalent to the positive control, butylated hydroxytoluene (BHT, p > 0.05), and was significantly higher than α-tocopherol (VE, p < 0.05). The reducing power of leaf extracts was as strong as roots (p > 0.05). HPLC and correlation analysis show that salvianolic acid B and rosmarinic acid constitute the most abundant phenolic compounds. They are the major contributors to antioxidant activities. The results suggested that S. miltiorrhiza leaves could be considered as a new potential source of natural phenolic antioxidants for food, pharmaceutical, cosmetics or nutraceutical industries.