The use of conventional extraction method particularly chromatography-based method involves complex scale-up, batch operation, low capability in process integration, laborious processing cycles, require high energy input and high cost (9). On the other hand, the removal of cell debris by filtration or centrifugation may be challenging when processing high biomass load due to heterogeneous distribution of particle size and high viscosity (10). On top of that, a higher number of operational steps would incur higher overall cost owing to the loss of some amount of target compound in each processing stage. In response to the increasing market demand of biotechnological products, a more versatile and economical bioseparation process which can offer higher process throughput, shorter processing time and scalability is necessary to cope with the current ratelimiting downstream processes (11). However, it should be noted that the selection of an appropriate separation method is crucial in the downstream processing. Otherwise, inappropriate extraction technique could negatively affect the biofunctionality of target molecules and would therefore limit their application to a great extent (12). Alternatively, ATPS exhibits application potential with great technical and economic advantages in downstream processing. Several discrete stages which involve separation, concentration into smaller volume and purification can be reduced and substituted by ATPS, allowing the overall recovery process become more energy-efficient and cost-effective (3). Compared to the conventional method, the use of ATPS for bioseparation offers many advantages (2). These include simple process operation, rapid separation, high selectivity, low energy consumption and low cost (3,8,13e16). ATPS has also been able to offer a biocompatible environment for the isolation of biotechnological products due to the presence of high water content in both phases (1,17). The extremely low interfacial tension of this system (between 0.0001 and 0.1 dyne/cm) creates high interfacial contact area of the dispersed phases, which in turn, enhances the efficiency of the mass transfer (1). Chemical cost is considered one of the dominant cost factors for large-scale bioseparation process. The use of inexpensive phase components in ATPS would make the whole downstream processing more economical. Problem of downstream pollution may also be avoided by recycling the ATPS phase components (2). Extraction using ATPS is relatively rapid and the processing capacity of this technological simple technique is quite high. Due to the simplicity and reliability of scaling-up approach, the extent of ATPS extraction to industrial scale application is feasible and practical (8,11,13).

Influence of parameters on the partitioning behavior of ATPS

The selective distribution of the compounds to be separated between the two phases serves as the basis of partitioning in ATPS. In ATPS, the partition profile of the solutes depends on different physicochemical interactions between the biomaterial and the phase forming chemicals (18). Interactions such as van der Waals’ forces, hydrogen bond, electrostatic interactions, steric effects, hydrophobicity, biospecific affinity interactions as well as conformational effects between the phase components and the substances contribute to the partitioning of the particular substance (1). To achieve an effective bioseparation process, the partitioning behaviour of biomolecule in ATPS can be influenced by changing some of the dominating factors such as molecular weights and size of polymers, type and composition of phase component, type of ions in the system, the addition of neutral salts like NaCl, tie line length (TLL), system temperature and pH (3,5,13).