Affinity precipitation is a simple, single plate separation process in which the complex of a smart macroaffinity ligand with the target protein (from a crude broth) can be selectively precipitated by application of a suitable stimulus. Alginate is a copolymer of guluronic acid and mannuronic acid residues and precipitates with Ca2+ ions. It was found to bind to pectinase present in a commercial preparation of Aspergillus niger, Pectinex Ultra-SPL. Microwave pretreatment of alginate at 75 degreesC was found to enhance the selectivity of the affinity precipitation. Using microwave-treated alginate, 83% of the enzyme activity with 20-fold purification could be recovered. SDS-PAGE upon silver staining confirmed the enhanced selectivity of affinity precipitation when microwave-treated alginate was used. (C) 2003 Elsevier Inc. All rights reserved.