Selective removal of polyphenols and brown colour in apple juices using PES/PVP membranes in a single ultrafiltration process

Polyphenols that are responsible for haze formation and browning during storage of clear apple juice and concentrates could be selectively removed by an ultrafiltration process using tailor-made membranes out of polyethersulfone (PES) and polyvinylpyrrolidone (PVP). The results were compared with commercial regenerated cellulose acetate membranes. The PES/PVP-membranes were prepared with different pore sizes by varying the polymer composition. This study has shown that, due to the adsorption capacity of PVP, the tailor-made membranes were more effective than the commercial regenerated cellulose membranes for the reduction of both polyphenols and yellowish brown pigments in apple juices. The flux was also significantly higher. Polyphenol removal rates from the model solution were up to 40% for a membrane prepared from a 22.5 wt.% polymer solution with a PES/PVP ratio of 3.5. Initial adsorption and flux values could be restored easily by regenerating the membranes in 0.1 M NaOH. (C) 2001 Elsevier Science B.V. All rights reserved.