BACKGROUND: The pentitol D-arabitol has been produced from D-glucose utilizing osmophilic yeast strains, however, there are remarkably few reports available on the production of D-arabitol from lactose. Previous studies in the laboratory have shown that the osmophilic yeast Kluyveromyces lactis NBRC 1903 can convert lactose to extracellular D-arabitol without extracellular accumulation of D-glucose or D-galactose. The present study was undertaken to determine the participation of aeration on the D-arabitol synthesis in K. lactis NBRC 1903. RESULTS: The highest D-arabitol concentration of 91.7 mmol L-1 was achieved after 120 h cultivation in medium containing 555 mmol L-1 of lactose with initial volumetric liquid-phase mass transfer coefficient of oxygen (k(L)a)(0) of 85.5 h(-1). The fractional yield of D-arabitol was affected by not only aeration but also growth phase. The highest fractional yield of D-arabitol in terms of lactose consumption was 0.255 that was obtained at stationary phase with (k(L)a)(0) of 85.5 h(-1). CONCLUSION: It was found that oxygen supply is a key factor in the production of D-arabitol. Patterns of metabolism were classified according to the level of oxygen supply and the growth phase. (C) 2010 Society of Chemical Industry