Backward extraction of reverse micellar encapsulated proteins using a counterionic surfactant

The back-extraction of proteins encapsulated in AOT reverse micelles was pe rformed by adding a counterionic surfactant, either TOMAC or DTAB. This nov el backward transfer method gave higher backward extraction yields compared to the conventional method with high salt and high pH of the aqueous strip ping solution. The protein activity was maintained in the resulting aqueous phase, which in this case had a near neutral pH and low salt concentration . A sharp decrease of the water content was observed in the organic phase c orresponding to protein back-extraction using TOMAC. The backward transfer mechanism was postulated to be caused by electrostatic interaction between oppositely charged surfactant molecules, which lead to the collapse of the reverse micelles. The back-extraction process with TOMAC was found to be ve ry fast; more than 100 times faster than back-extraction with the conventio nal method, and as much as 3 times faster than forward extraction. The form ation of 1:1 complexes of AOT and TOMAC in the solvent phase was observed, and these hydrophobic complexes could be efficiently removed from the solve nt using adsorption onto Montmorillonite in order for the organic solvent t o be reused. A second cationic surfactant, DTAB, confirmed the general appl icability of counterionic surfactants for the backward transfer of proteins . (C) 1999 John Wiley & Sons, Inc.