The possible mechanism of water transport from feed to osmotic agent side during forward osmosis in situation when feed contains high or low molecular weight compounds and their combination has been presented. The orientation of membrane was found to influence the transmembrane flux. When the feed contains mixture of low and high molecular weight compounds mode I (feed towards the support layer) was found to result in lower flux values as compared to Mode II (feed towards active layer) due to significant external concentration polarization. Forward osmosis resulted in the concentration of betalains content in beetroot juice and anthocyanin content in grape juice from 50.92 mg/L to 2.91 g/L (57.1 fold) and from 104.85 mg/L to 715.6 mg/L (6.8 fold), respectively. Total soluble solids in case of beetroot, grape and pineapple juice were found to increase from 2.3 to 52 degrees Brix, from 8.0 to 54.6 degrees Brix from 4.4 to 54 degrees Brix, respectively. (C) 2011 Elsevier Ltd. All rights reserved.