The concentration of anthocyanin extract from Garcinia indica Choisy (popularly known as kokum) was explored by forward osmosis process and compared with thermally concentrated sample. Mechanism of water transport from feed to osmotic agent side during forward osmosis in a situation when feed contains high or low molecular weight compounds was elucidated. The effects of membrane orientation, osmotic agent concentration, flow rates of feed and osmotic agent and temperature on transmembrane flux during the concentration of anthocyanin extract were studied. In a large-scale experiment, the anthocyanin extract was concentrated from 49 mg/l to 2.69 g/l (54-fold increase). Non-enzymatic browning index and degradation constant for thermally concentrated sample were found to be approximately two (0.78-0.35) and eight (63.0 x 10(-3) to 8.0 x 10(-3) day(-1)) times, respectively, as compared to the concentrate produced by forward osmosis. Ratio of HCA lactone to HCA was also found to be higher for the sample produced by thermal concentration (2.84:1) as compared to concentrate produced by forward osmosis (1.50:1). These results clearly indicate that the concentration of anthocyanin extract using forward osmosis has several advantages over the thermal concentration in terms of higher stability, lower browning index and less conversion of HCA to its lactone form. (C) 2009 Elsevier B.V. All rights reserved.