Purification, antioxidant activity and protein-precipitating capacity of punicalin from pomegranate husk

Punicalin is a kind of ellagitannin, existing in pomegranate husk, and has shown remarkable biological activities. A rapid and large-scale separation method of punicalin from pomegranate husk was established, using medium pressure liquid chromatography (MPLC). The optimal mobile phase consisted of 5% methanol and 0.1% (v/v) TFA in water, and the optimal loading amount and flow rate were 1.0 g and 80 ml/min, respectively. Under this condition, 339 mg of 95.9% punicalin could be obtained in 40 min. 59.7 mg of 78.0% gallic acid could be separated simultaneously. This method was practical for industrial utilisation of pomegranate husk. Afterwards, the antioxidant and protein-precipitating capacities of the purified punicalin, together with punicalagin, were evaluated. Results showed that punicalin had strong antioxidant activity, and it exhibited a low affinity for protein. This suggested that the antioxidant of punicalin would not be greatly masked by tannin–protein precipitation in application, and hence confirmed punicalin to be a promising antioxidant.