Materials
Dried mangosteen rind (Garcinia mangostana L.), a by-product of mangosteen-canning process, was supplied by a local manufacturer (Chanthaburi, Thailand). Sodium hydroxide (NaOH) and phosphoric acid (H3PO4) were obtained from Mallinckrodt Baker, Inc. (Phillipsburg, NJ, USA). Hydrogen peroxide (H2O2) and Congo red dye (C.I. 22120) were obtained from Merck KGaA (Darmstadt, Germany). Nile red dye and sodium azide (NaN3) were obtained from Sigma Chemical Company (St Louis, MO, USA). All reagents were of analytical grade and distilled water was used for preparation of all solution and emulsion. Soybean oil was purchased from a local supermarket and used without further purification.