Technological aspects of extractive fermentation using aqueous two-phase systems

Abstract

The efficiency of any fermentation process depends largely on downstream processing which ensures the purity and quality of the biochemicals. Since many biomolecules have narrow tolerance limits of pH, temperature, osmotic pressure, surface charges, etc. the extraction and isolation techniques should be specific and compatible to the product. Therefore, it is not surprising that about 60-90% of the cost of a biological process is that expended on downstream processing. Aqueous two-phase systems (ATPS) result from the incompatibility or immiscibility of polymers, either between two polymers in water or a polymer solution with a salt solution. ATPS contain about 80-90% water and thereby can provide an excellent environment for cells, cell organelles and biologically active substances. 'Extractive fermentation' is an emerging technique that involves the use of ATPS-based in situ fermentation processes. The advantages of such a system include rapid mass transfer due to low-interfacial tension, ease of operation under continuous mode, rapid and selective separation, biocompatibility, separation at room temperature, easy and reliable scale-up of bench scale results to production scale, ecofriendliness, suitability for systems with product inhibition and high yield of biomolecules. In this review, we will consider the basic principles involved and factors affecting extractive fermentation, technical aspects and technological developments like use of ligands and surfactants to improve separation, recent trends and future prospects of extractive fermentation systems. This review will also focus on the parameters responsible for better separation for in situ fermentation.