Sporamin is a storage protein in sweet potato tubers. In batch fermentation of recombinant Saccharomyces cerevisiae using selective yeast nitrogen base, the specific trypsin inhibitory activity of sporamin can reach a level of 463 U/g-cell and total volumetric activity of 1574 U/l. However, using non-selective YPAD medium (20 g/l glucose, 10 g/l yeast extract, 10 g/l peptone and 10 g/l ammonia sulphate), only lower specific activity of 344 U/g-cell but higher total activity of 2923 U/l was obtained. Using YPAD medium in fed-batch fermentation and controlling for different glucose concentrations within a specific pH range to reduce the accumulation of ethanol, glycerol and acetate, a specific sporamin activity of 347 U/g-cell and a total activity 6212 U/l was obtained with a glucose concentration of I g/l. An increase of specific activity to 831 U/g-cell and a total activity 12 222 U/l was obtained with a glucose concentration of 0.1 g/l. (C) 2002 Elsevier Science Ltd. All rights reserved.