Aqueous two-phase extraction, identification and antioxidant activity of anthocyanins from mulberry (Morus atropurpurea Roxb.)

Aqueous two-phase extraction (ATPE), identification and antioxidant activity of anthocyanins from mulberry (Morus atropurpurea Roxb.) were investigated in this study. The optimal differential partitioning of mulberry anthocyanins (MAY) and sugars was achieved in a system (pH 4.5, temperature = 35 ± 1 °C) composed of 30% (w/w) ethanol, 20% (w/w) concentration of ammonium sulphate, 10% (w/w) mulberry juice and 40% (w/w) water. The multiple partitioning indicated a single ATPE step could isolate the majority of anthocyanins, while removing near to 90% of the free sugars. The composition of the MAY extracted by ATPE had no obvious changes, and five anthocyanins were identified by HPLC–ESI-MS/MS. The ATPE extract showed a relatively high antioxidant ability compared to that by the conventional extraction. Our results indicated that ATPE was a valuable method for the removal of the majority of free sugars, which held great promise in the purification of natural anthocyanin pigments.