Behzad Mahdavi

Cationic balance in skim milk during bipolar membrane electroacidification

Abstract Bipolar membrane electroacidification (BMEA) technology has been applied to skim milk protein, in order to produce high purity casein isolates. BMEA uses a property of bipolar membrane to split water and the action of monopolar membranes for demineralization. When the H + are generated at the bipolar membrane, one cationic charge inherent to the solution being acidified must cross the cation exchange membrane (CEM) to keep the solution electrically neutral. The purpose of this study was to monitor the migration of charge through the CEM to counterbalance H + generated at the bipolar membranes. K + ions were identified as being the predominant ions that electromigrate from the skim milk solution until pH 5.0 is reached, at which point its concentration becomes insufficient to counterbalance H + . The other cations partially replaced K + to assure the electroneutrality of the solution. It appears that K + is a necessary ionic species to ensure the best efficiency of the BMEA and to limit the non-desired migration of H + across the CEM. Therefore, the electrical efficiency of BMEA is decreased by a loss of electrogenerated H + due to a lack of sufficiently mobile ions such as potassium. Consequently, the enrichment of the skim milk with some potassium would be required in order to obtain a better electrical efficiency.

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

Abstract A previous study on skim milk demonstrated that bipolar-membrane electroacidification (BMEA) is a technology that can be used to produce isoelectric precipitation of casein from milk. However, a deposit, suspected to be calcium hydroxide, was observed on the cation-exchange membrane (CEM) side in contact 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 therefore to evaluate two types of CEM with different permselectivities in terms of electrodialysis efficiency and membrane parameters. BMEA allowed the separation of high purity bovine milk casein (about 97% protein), and the permselectivity of both membranes tested does not influence the purity of the isolates produced. However, the migration of cations through the cationic membrane was found to be influenced by the permselectivity leading to isolates with different ash contents. The CSV™ membrane slowed down the migration of cations in comparison with CMX™ membranes. The membrane fouling of cation-exchange membrane was identified as precipitating calcium and magnesium hydroxides. Moreover, the fouling formed at the outer layer surface of the CEM was demonstrated to be reversible for both membranes while the fouling of the CSV™ membrane inner layer was irreversible.

Neutralization of hydroxide generated during skim milk electroacidification and its effect on bipolar and cationic membrane integrity

Abstract The aim of the present study was to evaluate the effect of neutralizing the OH− electrogenerated during bipolar membrane electroacidification (BMEA) on the integrity of the cationic and bipolar membranes used. The OH− were neutralized by acidification of the anionic side compartment of the bipolar membrane during BMEA of skim milk. The integrity of the membranes was characterized by membrane parameters and microscopic membrane surface elemental analysis and mapping. It appeared from these results that the resistance of cationic membranes increased, due to an exchange of monovalent counter-cations of the membrane by divalent cations less mobile and to a slight protein fouling. However, integrity and physical characteristics of bipolar membranes were preserved during BMEA.

Effect of added salt and increase in ionic strength on skim milk electroacidification performances

Bipolar-memibrane electroacidification (BMEA) technology which uses the property of bipolar membranes to split water and the demineralization action of cation-exchange membranes (CEM), was tested for the production of acid casein. BMEA has numerous advantages in comparison with conventional isoelectric precipitation processes of proteins used in the dairy industry. BMEA uses electricity to generate the desired ionic species to acidify the treated solutions. The process can be precisely controlled, as electro-acidification rate is regulated by the effective current density in the cell. Water dissociation at the bipolar membrane interface is continuous and avoids local excess of acid. In-situ generation of dangerous chemicals (acids and bases) reduces the risks associated with the handling, transportation, use and elimination of these products. The aim of this study was to evaluate the performance of BMEA in different conditions of added ionic strength (p(added) = 0, 0.25, 0.5 and 1.0 M) and added salt (CaCl2, NaCl and KCl). The combination of KCl and p(added) = 0.5 M gave the best results with a 45% decrease in energy consumption. The increased energy efficiency was the result of a decrease in the anode/cathode voltage difference. This was due to an increase of conductivity, produced by addition of salt, necessary to compensate for the lack of sufficiently mobile ions in the skim milk. However, the addition of salts, irrespective of type or ionic strength, increased the required operation time. The protein profile of isolates were similar under all experimental conditions, except at 1.0 M-CaCl2.