EFFECT OF DISSOLVED-OXYGEN LEVEL ON LACTASE PRODUCTION BY KLUYVEROMYCES-FRAGILIS

The influence of dissolved oxygen (% DO) on lactase production by Kluy veromyces fragilis (NRRL-Y-1109) in chemostat culture using a defined medium was studied. The aim was to determine conditions for both high specific enzyme activity and high volumetric enzyme productivity. Sign ificant differences in the specific enzyme activity and specific and v olumetric enzyme productivity were found at the corresponding steady s tates when the DO was varied between 0 and 90%. Maximum lactase produc tion was attained at 10% DO. Under this condition the best results wer e an enzyme activity of 5910 IU g(-1), specific production rate of 181 0 IU g(-1) h(-1) and volumetric production rate of 1530 IU dm(-3) h(-1 ). This seem to be due to the fact that at low aeration conditions the yeast metabolism is more reductive and as a consequence it verifies b oth higher specific lactose consumption rate and higher enzyme express ion than in full aeration conditions. The results of this investigatio n are also compared with those of other studies of lactase production by Kluyveromyces sp. (C) 1998 Society of Chemical Industry.