Characteristics of cross-flow filtration of pullulan broth.

Cross-flow filtration of culture broth from Aureobasidium pullulans, which elaborates pullulan, was done with a thin channel-type module and microfiltration membranes made of different materials and with different pore sizes. Various factors affecting the results of the filtration were studied. The specific resistance of the microbial cake was found to be higher than that of bakers' yeast, the cells of which are about the same size as an A. pullulans cell, and resistance increased with cultivation time. The flux and transmission of pullulan through the membrane decreased with cultivation time as the specific resistance increased. The flux and transmission of pullulan depended on the structure and pore size of the membrane and also on the pH of the broth. With a polysulphone membrane with a nominal pore size of 2.0 microns, transmission was nearly 100% with negligible leakage of cells and the flux was high when the pH of the broth was adjusted to 2.0.