## 2 Advancements in Ultrafiltration for Protein and Peptide Separation
### Combining Electrodialysis with Bipolar Membrane (EDBM) and UF  
Electrodialysis with bipolar membrane (EDBM) is conducted in a similar concept with EDUF, but with the objective of electroacidification by adjusting the H+ and OH- ions, generated from water splitting in anionic and cationic compartments using controlled current. In BM, AEM and CEM are laminated into a single membrane. The bipolar interface created by AEM and CEM forms a catalytic layer that induces an extensive water dissociation reaction when an electrical potential is applied to the electrode of EDBM. The free energy required, \(\Delta G\), for the water dissociation reaction is expressed as [106]:  
\[\Delta G=F\,\Delta\varphi=2.3\,R\,T\,\Delta pH \tag{9}\]  
where \(F\) is the Faraday constant, \(\Delta\varphi\) is the electrical potential difference between two solutions separated by the BM, \(R\) is the gas constant, \(T\) is the absolute temperature, and \(\Delta pH\) is the pH value difference between two solutions separated by BM. To illustrate, during dairy electroacidification, NaOH is liberated from the compartments of EDBM cells and can later be recycled for resolubilization. So, the minimum chemical is used compared to conventional acid precipitation that requires NaOH addition. Moreover, most of the coproduct from the base stream can be reutilized for caseinates [107]. With respect to other positive features such as increased protein content and better removal of antinutrients and minerals (calcium and magnesium), the performance of EDBM in dairy usage is commonly hampered by: (1) caseins clogging on spacers inside the EDBM stack and protein fouling on the bipolar membrane (BM) and cation-exchange membrane (CEM) and (2) scaling (mineral fouling) on the interface of the CEM [108; 109], which lead to low permeate flux and longer filtration time [110]. The clogging issue was successfully been addressed by coupling EDBM with UF. UF was used for treating input of hydrolysates or protein solution in a way that allows protein retention before electroacidification in EDBM stack. This method was capable of achieving thorough elimination of protein precipitation in dairy processing [111]. In soy protein concentrates consisting of 70% minimum protein content, despite encountering fouling, EDBM-UF produced low phytate content (lower than 1% \(w/v\)) and enhanced productivity and purity on account of demineralization [80]. In order to tackle persistent fouling problem, one study tried to incorporate discontinuous diafiltration (DDF), which was able to isolate higher protein concentration by minimizing carbohydrates and minerals. However, this failed to repair the problems in permeate flux of electroacidified feed [80]. Recently, treatment of soy protein extract at pH 6.0 with EDBM-coupled UF/DF by 100 kDa membrane was furthermore found to be best at producing isolate with the lowest phytic acid and increased solubility in a pH range of 2.0-4.0, compared to isoelectric precipitation at pH 4.5 and integrated UF/DF at pH 9.0 [112]. Researchers extended the exploration of how the sequence of embedded UF/DF process can be essential to the overall performance of integrated EDBM-UF/DF [113]. From all variation to attain final permeate volume 1.5-1.6 of feed, UF with VRF5 and continuous diafiltration (CDF) with VD 4 (volume diluted) suggested not only the most severe fouling and lowest permeate flux, but also the highest removal performances of phytic acid and carbohydrates, which were more than (1) UF-discontinuous diafiltration (DDF) with VRF 5 and re-VRF 5, (2) UF-CDF with VRF 2 and VD 2, and (3) UF-CDF with VRF 2 and double VRF 2 [113]. Various research studies explored the solution of another EDBM challenge, which is scaling on the CEM interface with its alkaline concentrate side owing to the facilitated mineral precipitation (see Figure 4) that set up the decrease of membrane permeslectivity and increased global resistance [114].