Antioxidant capacity of the extracts from pulp of Osmanthus fragrans and its components

In this study, a significant inhibitory effect (EC50 = 50.29 μg/ml) on the ABTS free radicals was detected in the crude ethanol extracts (CEE) of Osmanthus fragrans' pulp. Then, CEE was separated into methanol soluble fraction (MSF) and a methanol insoluble fraction (MISF), and their scavenging activities on the ABTS free radicals ascended in the order: MSF > CEE > MISF, respectively. Accordingly, the total phenolic (TP) contents of MSF, CEE and MISF were 40.53 ± 0.27, 35.37 ± 0.18 and 29.62 ± 0.23 mg/g (dry weight), respectively. Furthermore, salidroside (tyrosol 8-O-β-glucopyranoside), which showed powerful antioxidant activities in all test system was isolated from MSF. The antioxidant activity of salidroside (81.54 μg/ml) on DPPH free radicals was found to be nearly twice of that of MSF (144.78 μg/ml), and its total antioxidant activity is superior to that of the synthetic antioxidant butylated hydroxytoluene (BHT). In conclusion, our results suggested that O. fragrans' pulp, which was often considered as agricultural wastes, could be a promising source of natural antioxidants, and that MSF and salidroside may be good candidates for further development as natural antioxidants.