Comparison of Electrochemical and Chemical Acidification of Skim Milk

Functional Properties of Casein and Caseinate Produced by Electrodialysis with Bipolar Membrane Coupled to an Ultrafiltration Module

Electrodialysis with a bipolar membrane coupled to an ultrafiltration module (EDBM-UF) is a hybrid technology recently developed as an ecofriendly alternative to chemical acidification to produce casein and caseinate from skim milk. In this study, the composition and functional properties of casein and caseinate obtained by chemical acidification/basification and by the EDBM-UF method from winter and summer milks were analyzed and compared. Results show that the emulsifying properties, solubility, water holding, and gelling capacities are equivalent between casein and caseinate from both methods. However, the foaming properties of EDBM-UF ingredients were improved, and casein was less hygroscopic. Additionally, the season of milk influenced certain functional properties, such as water-holding capacity and hygroscopicity. Therefore, these results allow concluding that EDBM-UF ingredients have equivalent or higher functionality than chemically produced ingredients, and that the EDBM-UF process would be a more eco-efficient alternative to the chemical one.

Mathematical Modeling of the Effect of Pulsed Electric Field Mode and Solution Flow Rate on Protein Fouling during Bipolar Membrane Electroacidificaiton of Caseinate Solution

A one-dimensional non-stationary model was developed for a better understanding of the protein fouling formation mechanism during electroacidification of caseinate solution using electrodialysis with bipolar membranes (EDBM) in pulsed electric field (PEF) mode. Four different PEF modes were investigated with pulse–pause durations of 10 s–10 s, 10 s–20 s, 10 s–33 s, 10 s–50 s. For each current mode 3 different flow rates were considered, corresponding to Reynolds numbers, Re, equal to 187, 374 and 560. The processes are considered in the diffusion boundary layer between the surface of the cation-exchange layer of bipolar membrane and bulk solution of the desalination compartment. The Nernst–Planck and material balance equation systems describe the ion transport. The electroneutrality condition and equilibrium chemical reactions are taken into account. The calculation results using the developed model are in qualitative agreement with the experimental data obtained during the previous experimental part of the study. It is confirmed that both the electrical PEF mode and the flow rate have a significant effect on the thickness (and mass) of the protein fouling during EDBM. Moreover, the choice of the electric current mode has the main impact on the fouling formation rate; an increase in the PEF pause duration leads to a decrease in the amount of fouling. It was shown that an increase in the PEF pause duration from 10 s to 50 s, in combination with an increase in Reynolds number (the flow rate) from 187 to 560, makes it possible to reduce synergistically the mass of protein deposits from 6 to 1.3 mg/cm2, which corresponds to a 78% decrease.

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.

Production of calcium- and magnesium-enriched caseins and caseinates by an ecofriendly technology

Finding new environmentally friendly ways of producing proteins has never been of such critical public interest, both to meet consumers' needs and to preserve the environment. Milk proteins are among the most attractive protein types due to their high nutritional value and attractive functional properties. In this work, the separation of caseins by conventional chemical acidification was compared with electrodialysis with bipolar membrane coupled to an ultrafiltration module (EDBM-UF), a green process that allows the precipitation of caseins by H⁺ generated in situ by the bipolar membrane and, simultaneously, the production of a separated NaOH stream from OH^- electrogenerated by the bipolar membrane. Caseinate production using this NaOH stream by-product and the quantity of NaOH needed to produce caseinates from both methods were also investigated. Hence, the purity and composition of caseins and caseinates were compared in terms of protein, ash, and lactose contents as well as mineral composition. The results showed for the first time that caseinates can be produced by solubilizing caseins with NaOH stream from the EDBM process. Furthermore, the caseins and caseinates produced by EDBM-UF were equivalent in terms of lactose and protein contents to their respective caseins and caseinates that were chemically produced but presented slightly lower sodium content and 3 to 4 times higher magnesium and calcium contents. The fact that calcium and magnesium are likely bound to milk caseins would ensure their favorable absorbability. These caseins or caseinates from the new EDBM-UF process could be suitable as an improved protein-based calcium or magnesium supplement, both for their enhanced nutritional quality and because they are produced by a "green" process.

Bipolar membrane electroacidification of demineralized skim milk

The aim of this study was to evaluate the effect of decreasing the mineral content of skim milk by electrodialysis (ED) prior to electroacidification with bipolar membrane (BMEA) on the performance of the process, the chemical composition, and the physicochemical and functional properties of the isolates produced. ED used to demineralize the skim milk solution was very efficient. However, the electroacidification parameters were influenced by the demineralization level of the skim milk solution: the energy efficiency was decreased with an increase in demineralization, but it was still possible to perform BMEA at a very low conductivity level. Moreover, the isolates produced by BMEA after electrodialysis demineralization at different rates showed similar chemical composition, except on potassium and lactose contents for 75% demineralized isolate. These isolates, except on protein load for 75% demineralization rate, showed similar physicochemical and functional properties, whatever the demineralization rate.