Abstract

The effects of the most significant operational variables on reactor performance of fed-batch and repeated fed-batch were evaluated in the lactulose production by enzymatic transgalactosylation. Feed flowrate in the fed stage (F) and fructose to lactose molar ratio (Fr/L) were the variables that mostly affected the values of lactulose yield (Y-LU), lactulose productivity (pi(Lu)) and selectivity of transgalactosylation (S-Lu/(TOS)). Maximum Y-LU of 0.21 g lactulose per g lactose was obtained at 50% w/w inlet carbohydrates concentration (IC) of, 50 degrees C, Fr/L 8, F 1 mL.min(-1), 200 IU.g(Lactose)(-1) reactor enzyme load and pH 4.5. At these conditions the selectivity was 7.4, productivity was 0.71 g(Lu).g(-1).h(-1) and lactose conversion was 0.66. The operation by repeated fed batch increases the efficiency of use of the biocatalysts (E-B) and the accumulated productivity compared to batch and fed batch operation with the same biocatalyst. E-B obtained was 4.13 g(Lu).mg(biocatalyst)( protein)(-1), 10.6 times higher than in fed-batch.