Composition of anthocyanins in mulberry and their antioxidant activity

Anthocyanins in the fruits of mulberry (Morus alba L.) were extracted and separated by high-speed counter-current chromatography (HSCCC) using a biphasic solvent system composed of methyl tert-butyl ether–n-butanol–acetonitrile–water–trifluoroacetic acid (1:3:1:5:0.001) to yield five anthocyanins: cyanidin 3-O-(6″-O-α-rhamnopyranosyl-β-d-glucopyranoside) (C3RG), cyanidin 3-O-(6″-O-α-rhamnopyranosyl-β-d-galactopyranoside) (C3RGa), cyanidin 3-O-β-d-glucopyranoside (C3G), cyanidin 3-O-β-d-galactopyranoside (C3Ga) and cyanidin 7-O-β-d-glucopyranoside (C7G), respectively. The five compounds were identified by ESI–MS and one/two-dimensional NMR spectra. The antioxidant activity of crude mulberry anthocyanins (CMA), C3G, C3Ga, C7G, C3RG and C3RGa was investigated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging method. The results showed that CMA, C3G, C3Ga, C3G and C7G have higher scavenging ability on DPPH. At the concentration of 0.10 mg/mL, the DPPH radical scavenging rates of C3G, C3Ga and C7G were about 88% of vitamin C, while C3RG and C3RGa were about 60% of it. CMA had the same DPPH radical scavenging rate as vitamin C or the five anthocyanin monomers when the concentration reached 0.40 mg/mL, which shows that CMA is an excellent antioxidant agent.