Characterization of protein, peptide and amino acid fouling on ion-exchange and filtration membranes: Review of current and recently developed methods

• Protein, peptide and amino acid fouling characterization methods are summarized.
• Present and new characterization techniques are critically analyzed and discussed.
• Membranes used in an electromembrane processes are focused.
• Emerging characterization tools are presented.

Specific food proteins and peptides as well as amino acids released by enzymatic hydrolysis have demonstrated several biological activities, therefore they represent an interesting perspective in agrifood, biopharmaceutical and nutraceutical industries. However, these biomolecules are present at a significantly lower concentration in a complex mixture of different sizes, conformations and net charges. Separation or fractionation of such active molecules from the complex matrices is therefore vital in order to concentrate them in more purified form. In this context, conventional pressure-driven membrane processes like UF, NF and RO are widely used as a first choice for the separation and purification of proteins, peptides and amino acids. On the other side, innovative electromembrane processes such as EMF and EDFM are recently gaining much attentions and are regarded as favorable alternatives to the conventional methods. In addition, these methods could be potentially used for the efficient separation of charged compounds like proteins, peptides and amino acids. However, as observed for filtration membranes used in pressure-driven membrane filtration techniques (MF, UF, NF and RO), ion-exchange membranes stacked in an electrodialytic cell are also subject to fouling by protein, peptide and amino-acid. Indeed, fouling of ion-exchange membranes is a real challenge as these membranes are more easily affected and altered by aggressive chemical cleaning as compared to filtration membrane. Therefore, characterization of membrane fouling is essential to understand the mechanism of fouling to control this phenomenon. Consequently, this paper will review the conventional as well as more recent technologies used for the characterization of ion-exchange and filtration membranes fouling by proteins, peptides and amino acids. In addition, conventional methods of fouling characterization have been mainly developed for filtration membranes and information about the techniques that can be used in combination with ion-exchange membranes are still lacking. Accordingly, this work will create a bridge between the conventional and current characterization methods in relation to filtration as well as ion-exchange membranes. In addition, the pros and cons of each technique are discussed with some important points to be noted to avoid their misuse. Moreover, this paper will bring a clear insight about how the methods of fouling characterization have been evolving from qualitative to quantitative analyses. Till date, more than one method are used depending on nature of fouling, foulants and membrane used although, in-situ and non-destructive characterization methods are preferred.