Use of Tunable Copolymers in Aqueous Biphasic Systems for Extractive Bioconversion Aimed at Continuous Fructooligosaccharide Production

Abstract

Aqueous biphasic systems (ABSs) based on sodium polyacrylate (NaPA), ethylene oxide/propylene oxide (EO/PO) polymers, and (EO)x-(PO)y-(EO)x triblock copolymers were prepared and applied aiming at continuous fructooligosaccharide (FOS) production and separation. EO/PO hydrophilicity/hydrophobicity balance had a significant effect on ABS formation. To develop an integrated process including the continuous enzymatic (levansucrase) production of FOSs and their purification while improving the production yield by further glucose separation, the potential of these novel polymer-based ABSs as alternative platforms was investigated. They were used for the partitioning of different carbohydrates (FOS, sucrose, d-fructose, and d-glucose) and levansucrase. Results revealed a highly polymer-dependent partition of carbohydrates and a poorly dependent one of the enzymes. Changing EO/PO and copolymers, FOS was purified with high yields (72.94–100.0%). Using polypropylene glycol 400 + NaPA 8000-based ABS, the FOS was precipitated in the interphase and separated from the other components. Pluronic PE-6800 + NaPA 8000 was identified as the best ABS for FOS continuous production and in situ purification, while minimizing levansucrase inhibition by d-glucose. This system allowed selective partition of FOSs and d-glucose toward the top phase and that of levansucrase and its substrates toward the bottom one. COnductor-like Screening MOdel for Real Solvent (COSMO-RS) suggested that ABS formation may have been due to NaPA and polymer/copolymer competition to form hydrogen bonds with water molecules. Moreover, the partition of FOSs and sugar may have been the result of a subtle balance between hydrogen bonding of sugar and polymer/copolymer and electrostatic misfit of solute with NaPA. Finally, two integrated processes were proposed to be applied with real FOS extracts obtained by chemical or enzymatic hydrolysis of inulin or by transfructosylation of concentrated sucrose solutions using bacterial levansucrases.