Encapsulation of glucose oxidase (GOD) in polyelectrolyte complex capsules and its influence on properties of the enzyme is reported. The immobilization of GOD in the capsules made of sodium alginate (SA), cellulose sulfate (CS), poly(methylene-co-guanidine) (PMCG), CaCl2 and NaCl (GOD-SA-CS/PMCG capsules) was achieved using a one-step highly reproducible encapsulation protocol which was monitored by a Electrospray Ionization-Mass Spectrometry (ESI-MS). A leakage of the enzyme from the capsules was negligible. Encapsulated GOD exhibited higher thermostability, wider range of pH optimum and improved storage stability in comparison with free GOD. The 92% retained activity by the encapsulated GOD after 45 biooxidation cycles was markedly higher than that of the GOD entrapped in calcium pectate gel beads showing no activity after 12 cycles. Optimization of conditions of oxygen supplementation resulted in increased oxygen availability within the GOD-SA-CS/PMCG capsules. Oxygen supplementation was accompanied with a mild decrease in the mechanical resistance of the SA-CS/PMCG capsules. (C) 2007 Elsevier Inc. All rights reserved.