he stereospecific hydrolysis of cis-epoxysuccinate (CES) to L-(+)-tartrate, catalysed by the action of CES hydrolase activity in whole Nocardia tartaricans bacterial cells, has been chosen as a model biotransformation system. The performance of cells was studied by immobilization in polyelectrolyte complex (sodium alginate-cellulose sulfate-poly(methylene-co-guanidine, SA-CS/PMCG) capsules based on sodium alginate and cellulose sulfate as polyanions, poly(methylene-co-guanidine) as polycation, CaCl2 as gelling agent and NaCl as antigelling agent. The encapsulated cells showed a preservation of 80% of the initial catalytic activity in encapsulated cells compared with 15% of retained catalytic activity in free cells after 10 repeated biotransformation cycles. Uniformity of batches of capsules was achieved by the use of an air-stripping extrusion device fitted with a multiloop reactor. The capsules produced using this device had narrow standard deviations for capsule diameter (< 3%) and membrane thickness (< 6%). Monodisperse capsules are essential to ensure constant properties, including mechanical resistance and diffusional characteristics. Storage of capsules under different conditions revealed an approximate threefold decrease in bursting force after long-term exposure to the highly sequestering CES, compared with capsules stored in 0.9% (w/v) NaCl. The molecular weight cut-off of the capsular membrane, determined by inverse size exclusion chromatography, is in the range of the size of CES hydrolase. (c) 2006 Society of Chemical Industry.