Saccharomyces cerevisiae invertase was chemically modified with chitosan and further immobilized on sodium alginate-coated chitin support. The yield of immobilized protein was determined as 85% and the enzyme retained 97% of the initial chitosan-invertase activity. The optimum temperature for invertase was increased by 10 degrees C and its thermostability was enhanced by about 9 degrees C after immobilization. The immobilized enzyme was stable against incubation in high ionic strength solutions and was four-fold more resistant to thermal treatment at 65 degrees C than the native counterpart. The biocatalyst prepared retained 80% of the original catalytic activity after 50 h under continuous operational regime in a packed bed reactor. (c) 2005 Elsevier Inc. All rights reserved.