Effect of membrane permselectivity on the fouling of cationic membranes during skim milk electroacidification

A previous study on skim milk demonstrated that bipolar-membrane electroaci dification (BMEA) is a technology that can be used to produce isoelectric p recipitation of casein from milk. However, a deposit, suspected to be calci um hydroxide, was observed on the cation-exchange membrane (CEM) side in co ntact with the base, Also, the performance of the process decreased as well as the lifetime of the membrane. The aim of the present study was therefor e to evaluate two types of CEM with different permselectivities in terms of electrodialysis efficiency and membrane parameters, BMEA allowed the separ ation of high purity bovine mill, casein (about 97% protein), and the perms electivity of both membranes tested does not influence the purity of the is olates produced. However, the migration of cations through the cationic mem brane was found to be influenced by the permselectivity leading to isolates with different ash contents. The CSV(TM) membrane slowed down the migratio n of cations in comparison with CMX(TM) membranes. The membrane fouling of cation-exchange membrane was identified as precipitating calcium and magnes ium hydroxides. Moreover, the fouling formed at the outer layer surface of the CEM was demonstrated to be reversible for both membranes while the foul ing of the CSV(TM) membrane inner layer was irreversible. (C) 2000 Elsevier Science B.V. All rights reserved.