As lactose is the limiting substrate for microbial growth and its concentrations in the cheese whey varies between 4.0 and 5.0 g L1, it is necessary to make a preliminary concentration to reach the required values. As can be seen, the increase in the initial lactose concentration increased the cell and gum productivities. At S0¼10 g L1 and 30 g L1 the maximum gum productivities were around 7.3 and 21.9 g L1 h1 for 0.3oDo0.9 h1, respectively.