Phenolics were extracted from mangosteen fruit parts with 70% (v/v) aqueous acetone. The yield of crude
extracts of phenolics (CP) ranged from 5.8% to 7.9%. The total phenolics (TPH) content ranged from 9.3 mg
to over 250 mg of gallic acid equivalents per g of extract in the edible aril and skin, respectively. The formation
of phenolic–protein complexes was assayed by both the dye-labelled bovine serum albumin
(BSA) and the fluorescence quenching methods. Phenolics from peel and rind displayed a strong protein-precipitating
potential. On the other hand, phenolics from edible aril exhibited greater affinity for
BSA, as determined by the fluorescence quenching assay. The static quenching was the dominant mode
of quenching of BSA fluorescence by mangosteen fruit phenolics. Mangosteen phenolics occupied two
binding sites on BSA molecules located most likely in or near both tryptophan residues in the BSA molecule
acting as an intrinsic fluorescence probe.