## 2 Advancements in Ultrafiltration for Protein and Peptide Separation
### Charged-Membrane
Membrane UF can be charged with positive or negative moieties, and the details of preparation were published elsewhere [68]. However, mechanistic explanation of protein transmission is limited, excluding a study to correlate stagnant film model in charged UF membrane for multicomponent mixtures [69]. Therefore, a study with mechanistic approach to optimize the charged-membrane UF would be interesting to expand in the future. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Process** & **Feeds** & **Membrane and/or Protocols** & **Remarks** & **Ref** \\ \hline UF with charged membrane & \multirow{2}{*}{Why protein} & \multicolumn{2}{c}{Regenerated cellulose (RC), negatively charged 100 kDa (flat sheet/spiral-wound)} & Both modules retain 98\% of total whey proteins & \multirow{2}{*}{[62]} \\  & & \multicolumn{2}{c}{negatively charged 100 kDa (flat sheet/spiral-wound)} & 85\% higher flux than 10 kDa pristine membrane & \\ \hline  & \(\alpha\)-lactalbumin and \(\beta\)-lactoglobulin & RC, positively charged 300 kDa (two-staged UF) & 490\% improvement of selectivity to retain \(\beta\)-lactoglobulin. & \multirow{2}{*}{[70]} \\  & & \(\beta\)-lactoglobulin & (two-staged UF) & Purity of \(\alpha\)-lactalbumin: 87\% & \\ \hline  & Milk serum permeate & RC, positively charged 300 kDa (three-staged UF) & 180\% improvement of selectivity to retain \(\beta\)-lactoglobulin. & \multirow{2}{*}{[71]} \\  & & \(\beta\)-lactoglobulin & (three-staged UF) & Purity of \(\alpha\)-lactalbumin: 87\% & \\ \hline  & Lysozyme and \(\begin{array}{c}\\ \text{lactoferrin}\end{array}\) & \begin{tabular}{c} Zirconia, positively grafted \\ 300 kDa by ethylenediamine \\ 1000 V m\end{tabular} & \begin{tabular}{c} Lysozyme transmission \\ selectivity up to 165 \\ 100\% purity in permeate \\ \end{tabular} & \multirow{2}{*}{[72]} \\ \hline EUF & BSA & \begin{tabular}{c} Continuous current, PS \\ (polysulfone) 100 kDa, effective \\ area 45 cm\({}^{2}\), 3000 V m\({}^{-1}\) \\ \end{tabular} & \begin{tabular}{c} Reduction of 80\% in BSA \\ concentration time (from \\ 0.5–1.0 g L\({}^{-1}\)) \\ \end{tabular} & \multirow{2}{*}{[73]} \\  & BSA and lysozyme & \begin{tabular}{c} External DC current, PES \\ (polytecharsulfone) 30 kDa, \\ effective filtration area: 132 cm\({}^{2}\), \\ 1000 V m\({}^{-1}\) \\ \end{tabular} & \multirow{2}{*}{[74]} \\  & & \begin{tabular}{c} Pulsed electric fields, fluoride \\ polyvinylden flat sheet 25 kDa, \\ effective filtration area: 51 cm\({}^{2}\), \\ 700 V m\({}^{-1}\) \\ \end{tabular} & A 300\% increase in permeate flux & \multirow{2}{*}{[75]} \\  & BSA and lysozyme & \
\begin{tabular}{c} Electrodialysis integration, UF \\ membrane: PES 30 kDa, effective \\ filtration area: 35 cm\({}^{2}\), 150 mA \\ \end{tabular} & Permeate flux increase by 20\% & \multirow{2}{*}{[76]} \\ \hline EDUF & \(\alpha\)-lactalbumin and \(\beta\)-lactoglobulin &
\begin{tabular}{c} CA, 100 kDa (elution mode), \\ membrane active area: 35 cm\({}^{2}\), \\ 3–22 A m\({}^{-2}\), 100–800 V m\({}^{-1}\) \\ \end{tabular} & Separation factor of 1.2 reached & \multirow{2}{*}{[77]} \\  & & \(\beta\)-lactoglobulin & 3–22 A m\({}^{-2}\), 100–800 V m\({}^{-1}\) & \(\alpha\)-lactalbumin (optimum) & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Representative works of protein ultrafiltration advancements.