Effects of drying methods on assay and antioxidant activity of xanthones in mangosteen rind

Rind of mangosteen is one of the best natural sources of xanthones, which have been reported to have high antioxidant activity. In many cases mangosteen rind must be dried prior to extraction of the active compounds. However, information on the effects of different drying methods and conditions on the retention of xanthones in mangosteen rind is still very limited. This work was therefore aimed at studying the effects of selected drying methods and conditions on the changes of the contents as well as the antioxidant activity of xanthones in mangosteen rind. Mangosteen rind was subject to hot-air drying, vacuum drying or low-pressure superheated steam drying (LPSSD) at 60, 75 and 90 °C and in the case of sub-atmospheric drying methods at an absolute pressure of 7 kPa. The xanthones contents were analysed by HPLC, while their antioxidant activity was assessed by DPPH radical scavenging capacity and ABTS assays. The results showed that the drying methods significantly affected degradation of xanthones (i.e., α-mangostin and 8-desoxygartanin) and their antioxidant activity. Either hot-air drying or LPSSD at 75 °C is proposed as an appropriate drying technique and condition to preserve xanthones in mangosteen rind.