Amylase partitioning and extractive bioconversion of starch using thermoseparating aqueous two-phase systems

Abstract

The effectiveness of thermoseparating polymer-based aqueous two-phase systems (ATPS) in the enzymatic hydrolysis of starch was investigated. In this work, the phase diagrams of PEO–PPO-2500/ammonium sulfate and PEO–PPO-2500/magnesium sulfate systems were determined at 25 °C. The partition behavior of pure α-amylase and amyloglucosidase in four ATPS, namely, PEO–PPO/(NH 4) 2SO 4, PEO–PPO/MgSO 4, polyethylene glycol (PEG)/(NH 4) 2SO 4, and PEG/MgSO 4, was evaluated. The effects of phase-forming component concentrations on the enzyme activity and partitioning were assessed. Partitioning of a recombinant, thermostable α-amylase (MJA1) from the hyperthermophile, Methanococcus jannaschii was also investigated. All of the studied enzymes partitioned unevenly in these polymer/salt systems. The PEO–PPO-2500/MgSO 4 system was extremely attractive for starch hydrolysis. Polymer-based starch hydrolysis experiments containing PEO–PPO-2500/MgSO 4 indicated that the use of ATPS had a significant effect on soluble starch hydrolysis. Batch starch hydrolysis experiments with PEO–PPO/salt two-phase systems resulted in higher production of maltose or glucose and exhibited remarkably faster hydrolysis. A 22% gain in maltose yield was obtained as a result of the increased productivity. This work is the first reported application of thermoseparating polymer ATPS in the processing of starches. These results reveal the potential for thermoseparating polymer-enhanced extractive bioconversion of starch as a practical technology.