Baicalein, showing stronger pharmacological activity, can be obtained by removal of the distal glucuronic acid (GluA) from baicalein 7-O--D-glucuronide (baicalin). In the present study, a chemically defined reaction medium comprised of mildly acidic (pH 4.5, 37 degrees C) aqueous solution, was formulated for biotransformation of baicalin to baicalein using acidic Helix pomatia derived beta-glucuronidase (HP-GUS), an untested biocatalyst source. The biotransformation was carried out as a batchwise process within an optimised reaction cocktail (with 5% dimethylformamide, v/v) by a 4-h HP-GUS (250 unit/ml) incubation of baicalin (60ppm) and resulted in a promising conversion ratio of 99% without any by-product formation. The formulated reaction system may offer a novel and efficient alternative for bioproduction of baicalein, which can be vital for pharmaceutical applications. [GRAPHICS] .