The objective of this research was the production of a banana extract containing no polyphenol oxidase by ultrafiltration. Banana juice was extracted after inhibition of polyphenol oxidase using a solution containing 0.15 g per 100 ml of sodium metabisulphite and 1 g per 100 ml of ascorbic acid in distilled water to avoid initial browning. Polyphenol oxidase was then retained by ultrafiltration using polysulphone membranes with a cut-off of 20 kDaltons. Two transmembrane pressures, 600 and 800 kPa, were used but 600 kPa was preferred because of the more stable permeate flux which decreased less with time and concentration of extract. (C) 1999 Society of Chemical Industry.795643647