Antioxidant activities and polyphenol content of Morus alba leaf extracts collected from varying regions

Morus alba leaf (MAL), also known as Mori folium when used as a herbal medicine, has traditionally been used in Chinese medicine to treat diabetes, protect the liver and lower blood pressure. In the present study, MAL was collected from various regions in Korea and the antioxidant activity, total polyphenol contents and main flavonoid contents was investigated. MAL were collected from various areas in Korea and extracted with methanol. The total polyphenol contents were evaluated based on the Folin-Ciocalteu method using a spectrophotometer. The antioxidant activities were determined by a 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay method. The identification and quantification of three main polyphenol constituents was performed using high-performance liquid chromatography/diode array detection analysis. The total polyphenol contents of the MAL extracts varied between 23.2 and 55.4 mg gallic acid equivalent/g. The radical scavenging activity (SC50) of the MAL extracts ranged between 584 and 139 μg/ml. Three flavonol compounds (rutin, isoquercitrin and astragalin) were identified as main polyphenol constituents. These contents varied from 0.68–12.7, 0.69–9.86 and 0.05–3.55 mg/g, respectively. The average of the total was 9.52 mg/g, which was similar to that of commercial MAL extracts (10.58 mg/g). Among the three flavonol compounds, isoquercitrin showed the highest content (5.68 mg/g) followed by rutin (3.1 mg/g) and astragalin (2.4 mg/g). In the present study, the radical scavenging activity, polyphenol content and flavonol content of MAL were significantly different according to growing area. These three flavonol compounds were identified as main constituents of MAL in this study, and are known to have various biological activities, as well as strong antioxidant activities. Therefore, the sum of these three flavonol compounds was indicated as a good marker for the quality control of Mori folium.