Upgrading of orange pulp suspension by enrichment with kefir was investigated and the effects of initial sugar concentration, pH, aeration and the addition of molasses on kefir growth were monitored. Higher maximum growth rate mu(max) for kefir was observed when initial sugar used was 75 g/l. Both 75 g/l and 90 g/l initial sugar contents of kefir resulted in higher final biomass concentration and daily biomass productivity. At an initial sugar concentration > 75 g/l, however, high residual sugar and ethanol concentrations were observed. Air flow rate and pH affected kefir's p while the addition of molasses had no effect on growth. Potential application of upgraded orange pulp in bread-making was examined. Bread produced by immobilized kefir on orange pulp had an improved aromatic profile in comparison with bread produced by baker's yeast, and preliminary sensory evaluation of the produced bread was acceptable. (c) 2007 Elsevier Ltd. All rights reserved.