The soluting effect can be defined as the effect of a solute on the activity coefficient and solubility of another solute in a solution. Reducing the solubility and increasing the activity coefficient of a solute due to the addition of another solute is called the soluting-out effect, and inversely the soluting-in effect corresponds to increasing the solubility. Aqueous biphasic systems (ABSs) formation, which is a kind of soluting-out phenomenon, appears when combinations of two hydrophilic solutes display incompatibility in aqueous media above critical concentrations. The two aqueous phases coexisting in ABS give different physicochemical environments, thus allowing the unequal partition of target compounds. The proper selection of the phase forming components leads to the adjustable nature of ABS for handling the partition trend, authorizing thus the development of satisfactory extraction platforms. The recovery and the purification of bioproducts from natural sources, called downstream processing, usually account for the most cost of biomaterial production. Despite high popularity, chromatography-based strategies suffer some disadvantages regarding complexity and time- and cost-intensity, therefore, they cannot be used for downstream operations without coupling with other methods. This fact raises the requirement for alternative/complementary techniques for enhanced downstream strategies. ABSs are biocompatible, scalable, and energy-, time-, and cost-effective separation techniques proved to be suitable in downstream strategies as primary recovery stage. Liquid-liquid extraction based on ABSs has superiority over customary extraction involving organic solvents in terms of product bioactivity retention and environmental health.
