A transferase was isolated, purified and characterised from Aspergillus aculeatus. The enzyme exhibited a pH and temperature optima of 6.0 and 60 degrees C, respectively and under such conditions remained stable with no decrease in activity after 5 h. The enzyme was purified 7.1 fold with a yield of 22.3% and specific activity of 486.1 U mg(-1) after dialysis. concentration with polyethyleneglycol (30%) and DEAE-Sephacel chromatography. It was monomeric with a molecular mass of 85 kDa and K(m) and V(max) values of 272.3 mM and 166.7 pmol min(-1) ml(-1). The influence of pH, temperature, reaction time, and enzyme and sucrose concentration on the formation of short-chain fructooligosaccharides (FOS) was examined by statistical response surface methodology (RSM). The enzyme showed both transfructosylation and hydrolytic activity with the transfructosylation ratio increasing to 88% at a sucrose concentration of 600 mg ml(-1). Sucrose concentration (400 mg ml(-1)) temperature (60 C), and pH (5.6) favoured the synthesis of high levels of GF(3) and GF(4). Incubation time had a critical effect on the yield of FOS as the major products were GF(2) after 4 h and GF4 after 8 h. A prolonged incubation of 16 h resulted in the conversion of GF(4) into GF(2) as a result of self hydrolase activity. (c) 2008 Elsevier Ltd. All rights reserved.