Bipolar Membrane Electroacidification Research Articles

Fouling Mitigation by Optimizing Flow Rate and Pulsed Electric Field during Bipolar Membrane Electroacidification of Caseinate Solution

The efficiency of separation processes using ion exchange membranes (IEMs), especially in the food industry, is significantly limited by the fouling phenomenon, which is the process of the attachment and growth of certain species on the surface and inside the membrane. Pulsed electric field (PEF) mode, which consists in the application of constant current density pulses during a fixed time (Ton) alternated with pause lapses (Toff), has a positive antifouling impact. The aim of this study was to investigate the combined effect of three different relatively high flow rates of feed solution (corresponding to Reynolds numbers of 187, 374 and 560) and various pulse–pause ratios of PEF current regime on protein fouling kinetics during electrodialysis with bipolar membranes (EDBM) of a model caseinate solution. Four different pulse/pause regimes (with Ton/Toff ratios equal to 10 s/10 s, 10 s/20 s, 10 s/33 s and 10 s/50 s) during electrodialysis (ED) treatment were evaluated at a current density of 5 mA/cm2. It was found that increasing the pause duration and caseinate solution flow rate had a positive impact on the minimization of protein fouling occurring on the cationic surface of the bipolar membrane (BPM) during the EDBM. Both a long pause and high flow rate contribute to a more effective decrease in the concentration of protons and caseinate anions at the BPM surface: a very good membrane performance was achieved with 50 s of pause duration of PEF and a flow rate corresponding to Re = 374. A further increase in PEF pause duration (above 50 s) or flow rate (above Re = 374) did not lead to a significant decrease in the amount of fouling.

Impacts of Flow Rate and Pulsed Electric Field Current Mode on Protein Fouling Formation during Bipolar Membrane Electroacidification of Skim Milk.

Fouling is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect of five different solution flow rates (corresponding to Reynolds numbers of 162, 242, 323, 404 and 485) combined with the use of pulsed electric field (PEF) current mode on protein fouling of bipolar membrane (BPM) during electrodialysis with bipolar membranes (EDBM) of skim milk. The application of PEF prevented the fouling formation by proteins on the cationic interface of the BPM almost completely, regardless of the flow rate or Reynolds number. Indeed, under PEF mode of current the weight of protein fouling was negligible in comparison with CC current mode (0.07 ± 0.08 mg/cm2 versus 5.56 ± 2.40 mg/cm2). When a continuous current (CC) mode was applied, Reynolds number equals or higher than 323 corresponded to a minimal value of protein fouling of BPM. This positive effect of both increasing the flow rate and using PEF is due to the facts that during pauses, the solution flow flushes the accumulated protein from the membrane while in the same time there is a decrease in concentration polarization (CP) and consequently decrease in H+ generation at the cationic interface of the BPM, minimizing fouling formation and accumulation.

Relative contributions of charged species to conductivity changes in skim milk during electrochemical acidification

Bipolar membrane electroacidification (BMEA) is an acidification technique that approximates chemical acidification. However, differences in the casein precipitation profile have been observed between these two procedures and correlated with differences in conductivity. In this work, ionic and protein contributions to conductivity during BMEA were mathematically modeled. Chloride, potassium, calcium and sodium made major contribution during electrochemical acidification. The evolution of protein contribution was the same as observed previously for chemical acidification, but with slightly higher values. During pH decrease, chloride contribution to conductivity was greater during chemical acidification while the decrease in potassium contribution was more marked during BMEA. Since the contribution of proteins during BMEA was greater, electrostatic repulsions between proteins would also be greater than during chemical acidification, explaining their precipitation at a higher pH value.

Utilization of tofu whey pre-treated by electromembrane process as a growth medium for Lactobacillus plantarum LB17

Lactobacillus plantarum is a probiotic microorganism which can use oligosaccharides like stachyose and raffinose during fermentations. Tofu whey (TW), a by-product of tofu production, is a good source of carbohydrates, mainly sucrose, raffinose and stachyose, as well as protein and magnesium (from the coagulant agent). In this context, the objectives of this study were to study the efficiency of electromembrane processes on salt (conventional electrodialysis) and protein (bipolar membrane electroacidification) recovery from the TW and to evaluate the potential of a partially demineralized pre-treated TW as a growth medium for L. plantarum. It appeared that skimming and demineralization of the TW allowed the recovery of almost 45% and 54% of the initial proteins and minerals contents respectively. However, the electroacidification process was inefficient for the precipitation of residual proteins in the TW. The demineralization level of the TW did not have a significant effect on the viable counts obtained for L. plantarum in demineralized skimmed tofu whey (DSTW)-based media. During fermentations, more than 60% of the initial contents of stachyose, raffinose and sucrose in TW were metabolized by the bacteria. These results suggest that the DSTW could be used as a potential low cost growth medium for lactobacilli and that the coagulant agent and protein recovered could be reused in tofu process to increase yield.

Delipidation of a Whey Protein Concentrate by Electroacidification with Bipolar Membranes

The separation of residual fats from whey protein concentrates (WPC) results in a better nutritional and functional utilization of this product. Bipolar membrane electroacidification (BMEA) technology allows acidification and demineralization of solutions without any salt addition. The principle of BMEA is based on proton formation from water molecule dissociation at the bipolar membrane interface. The objective of this work was to determine the effect of an electroacidification treatment at pH 4.5 on the precipitation of lipids. WPC electroacidification was carried out with or without preliminary demineralization by conventional electrodialysis. The effect of ionic strength on lipid precipitation rates was also evaluated by dilution of the WPC samples. Lipid precipitation levels of 35-39% were obtained using the electroacidification process without a dilution step, while the combination of BMEA and dilution of the WPC resulted in a decrease in lipid content by six-fold from 0.76 to 0.21%.

Chitosan solubilization by bipolar membrane electroacidification: Reduction of membrane fouling

Chitosan, a biopolymer obtained from chitin deacetylation, was solubilized by bipolar membrane electroacidification (BMEA). We showed earlier that limitation in solubilization process was mainly due to chitosan precipitation in the acidified compartment. If fouling can be reduced or prevented, BMEA could be an environmentally attractive method for chitosan solubilization. The purpose of the present work was to identify process conditions that could reduce chitosan fouling in BMEA. The factors studied were: the type of salt in the acidified compartment (NaCl or CH 3COONa); the type of electrolyte in the basified compartment (KCl or HCl); and the current density (4 or 20 mA/cm 2). Chitosan fouling was successfully reduced by a combination of NaCl salt and HCl electrolyte, while 98% chitosan solubilization yield was achieved by operating at a current density of 4 mA/cm 2 with NaCl/KCl configuration with no apparent fouling. This work showed that water dissociation at the interface of the anionic membranes was the main factor responsible for chitosan precipitation.

Solubilization of Chitosan by Bipolar Membrane Electroacidification

Chitosan, a partially deacetylated derivative of chitin, was solubilized by bipolar membrane electroacidification (BMEA). Bipolar/monopolar (anionic or cationic) configuration and chitosan addition mode (single step or stepwise) were examined. Chitosan solubility and electroacidification parameters were monitored during the process to determine the optimal conditions. Bipolar/anionic configuration and stepwise feeding mode led to chitosan solubilization yield of 91% in 60 min at 20 mA/cm(2). In this configuration, chitosan solution had a pH of 2.5, a conductivity of 8.5 mS/cm, and an ash content of 0.2%. Relative energy consumption was 0.05 kWh/L of 1% chitosan solution prepared. Although some chitosan particles were aggregated in the electrodialysis stack, limiting chitosan solubilization, BMEA allowed complete solubilization of chitosan circulating in the system.

Precipitation of Cheddar Cheese Whey Lipids by Electrochemical Acidification

Lipid separation from cheddar cheese whey allows a better valorization of protein fractions. In this study, bipolar membrane electroacidification (BMEA) was used to obtain precipitates with a high level of lipids. Whey samples with normal and low (by way of electrodialysis) mineral salt levels have been treated by a BMEA process and centrifuged. The composition of flocs and precipitation yields were determined. The BMEA process increased lipid precipitation rates by almost 50% in comparison with a centrifugation step only whereas a demineralization step prior to electroacidification had a limited effect on the precipitation level. Precipitates obtained were mainly composed of lipids (probably phospholipids) but also contained proteins. BMEA of cheddar cheese whey would allow the production of a lipid-enriched fraction and of a protein-enriched whey.

Relationship between electrical conductivity and demineralization rate during electroacidification of cheddar cheese whey

Electrical conductivity is used as a simple method to monitor demineralization of food systems during conventional electrodialysis treatments. However, during bipolar membrane electroacidification, the H + generated at the bipolar membrane, have a higher conductivity contribution in comparison with all other cations. The objective of the present work was to develop an equation correlating conductivity and temperature to the demineralization rate in cheddar cheese whey during bipolar membrane electroacidification treatment. It appeared that conductivity data were not directly correlated with experimental demineralization rate. Thus a second order polynomial equation appropriate for whole and skim whey, was developed in order to predict demineralization rate ( D) as a function of conductivity ( C) and temperature ( T): D = 153.42 − 64.45 C + 5.55 T + 2.97 C 2 − 0.03 T 2 ( R 2 = 0.946). Mathematical models were also calculated from data of diluted whey solutions and these equations allowed evaluation of dilution phenomenon due to dead volume in electrodialysis cell prior to electroacidification. This work will allow the use of conductivity and temperature measurements to indicate, more precisely, the demineralization rate of cheddar cheese whey during electroacidification with bipolar membrane.

Effect of conductivity control on the separation of whey proteins by bipolar membrane electroacidification.

Since the limiting factor of the bipolar membrane electroacidification (BMEA) process at 20% WPI (whey protein isolate) was hypothesized to be the lack of mobile ion inherent to the protein solution at pH 5.0, the aim of the present work is to study the effect of the conductivity control on the precipitation behavior of whey protein. BMEA performances were evaluated by measuring electrodialytic parameters, protein kinetic precipitation, molecular profiles, and isolate chemical composition and purity. The highest protein precipitation with 10% WPI solution was obtained at pH 4.6 and at a conductivity level of 200 microS/cm maintained with many 0.4-mL additions of 1.0 M KCl (200 microS[+]), with a 46% precipitation of the total protein, beta-lg composing the main part of the precipitated protein. With a 20% WPI solution, it was possible to reach pH 4.65 with conductivity control at 350 microS/cm. However, the 27% protein precipitation was still low. The changes in viscosity as pH decreases observed at 20% WPI would decreased the final precipitation rate of beta-lg, since the viscosity of the 20% WPI dispersion was very different.

Fractionation of whey proteins by bipolar membrane electroacidification

Bipolar membrane electroacidification (BMEA) is a technology offering the coupled effect of demineralization and acidification by using the properties of bipolar membranes to dissociate water molecules at their interfaces and of cation exchange membranes (CEM) to demineralize by migration of low molecular weight ionic species. The aim of the present study was to demonstrate the feasability of BMEA to fractionate whey proteins and to study the effect of protein concentration on its performance in comparison with chemical acidification. These results demonstrated the feasability of BMEA for whey protein separation and the influence of the initial protein concentration on the purity and yield of the separated fraction. At 5% whey protein isolate (WPI) initial concentration, this technology allows the separation of 98% pure β-lactoglobulin (β-lg) fraction with a 44.0% recovery yield. At 10% WPI initial concentration, BMEA allows the production of a β-lg-enriched fraction containing 97.3 of β-lg and 2.7% α-lactalbumin (α-la), for a 98% total protein purity.

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

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.

Comparison between reconstituted and fresh skim milk chemical and electrochemical acidifications

AbstractThe aim of this study was to compare the electrochemical and chemical acidification of reconstituted and fresh skim milk in terms of electrodialytic parameters, precipitation kinetics, chemical composition and physicochemical and functional properties of isolates produced by bipolar membrane electro acidification (BMEA). The electrodialytic parameters were not influenced by the type of milk when both milks were compared at a similar protein and salt content. The difference in precipitation kinetics observed between the two milks, whatever the acidification procedure, can be explained mainly by a difference in salt content. Isolates produced by BMEA showed similar physicochemical and functional properties (except for foaming capacity) to isolates produced chemically. The main factor affecting the composition and the physicochemical and functional properties was the pre‐treatment of milk prior to acidification: it had a higher impact on the functional properties than the acidification treatment itself.Copyright © 2002 Crown in the right of Canada. Published for SCI by John Wiley & Sons, Ltd

Identification of Skim Milk Electroacidification Fouling: A Microscopic Approach

Bipolar membrane electroacidification (BMEA) was used to produce high-purity bovine milk casein isolates. However, a deposit suggested to be a mix of calcium and magnesium salts was observed on the cation-exchange membrane (CEM) side in contact with the base. The aim of the present study was to complete the identification of the deposit formed on CMX membrane during bipolar membrane electroacidification of skim milk, and to characterize its physical structure at the interfaces of CEM. The results showed that a calcium deposit was found on both sides of the membranes as well as inside the membrane. This fouling was identified as calcium carbonate, but was likely a mix between calcium carbonate and hydroxyde.

Comparison of Electrochemical and Chemical Acidification of Skim Milk

ABSTRACT:The purpose of this study was to compare chemical and electrochemical acidification, in order to identify differences between the two acidification procedures. The results reveal differences in the acidification profiles obtained with the two methods. Whereas chemical acidification showed a salting‐in effect from addition of salts, bipolar‐membrane electroacidification (BMEA) removes salts through electrochemical demineralization, favoring protein precipitation. Hence, at pH 4.6, all the caseins were precipitated by BMEA, while some were not yet precipitated by chemical acidification. Nevertheless, the chemical composition and the casein fraction composition of the isolates were the same for both chemical and electrochemical acidification.

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

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.

Effect of cationic membrane permselectivity on the efficiency of skim milk electroacidification.

Bipolar membrane electroacidification (BMEA) uses the property of bipolar membranes to split water and the demineralization action of cation-exchange membranes (CEM). As milk mineral salt content is very sensitive to ionic strength and pH changes, the aim of this study was to better understand the effect of changes in mineral content during pH decrease and demineralization of skim milk. The objectives were to investigate the effect of different cationic permselective membranes (CSV and CMX membranes) on skim milk cation migration and protein precipitation during BMEA. The permselectivity of both membranes tested does not influence the final efficiency of BMEA. The purity of the bovine milk casein isolates produced was similar to or higher (97-98% versus 93.4-96.7) than those of commercial isolates, due to a reduced ash content (1.2 versus 2.0-3. 8%) resulting from the CEM demineralizing phenomenon. For both membranes, the main ionic species to migrate was the potassium ions.

Cationic balance in skim milk during bipolar membrane electroacidification

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 temperature on the separation of soybean 11 S and 7 S protein fractions during bipolar membrane electroacidification.

The purpose of this study was to evaluate the effect of temperature (10 and 27 degrees C) on the efficiency of bipolar membrane electroacidification (BMEA) to fractionate soybean proteins. BMEA is a technology derived from electrodialysis, based on the isoelectric precipitation of proteins. It appears that temperature has a significant effect on the selective precipitation of the soybean protein fractions, mainly 11 S and 7 S, during BMEA. At 27 degrees C, the precipitation profile of the four protein fractions is situated in a pH range from 6.6 to 4.4, with no possibility of separating any of theses fractions. However, at 10 degrees C, the 11 S globulin precipitates at a higher pH than at 27 degrees C, pH 6.7 vs 5.9, allowing the fractionation of 11 S from the other fractions. Using electroacidification it is possible to obtain a precipitate solution enriched in the 11 S fraction (71.8% of 11 S and 10.8% of 7 S) and a supernatant solution enriched in the 7 S fraction (46.6% of 7 S and 4.6% of 11S).

Bipolar membrane electroacidification to produce bovine milk casein isolate.

Bipolar membrane electroacidification (BMEA) has been developed previously (Bazinet et al., Report for the Canadian Electricity Association 9326 U 987, 1996; Bazinet et al., J. Agric. Food Chem. 1997, 45, 2419-2425, 3788-3794) and has been used for isoelectric precipitation of soybean proteins. The purpose of this study was to validate the feasibility of BMEA for the precipitation of milk casein and to investigate the effect of flow rate. High-purity isolates containing 1.23 and 2.00% ash and 85.4 and 91.6% total protein were obtained with flow rates of 0.2 and 1.2 gal/min. The molecular composition profiles of the isolates obtained by HPLC showed that only caseins were precipitated. However, except for protein precipitation curves, the flow rate did not influence the final composition and purity of the isolates. These results showed that BMEA is a new alternative process for the production of high-purity bovine milk casein isolate.