The K5 polysaccharidic antigen obtainable from a strain of Escherichia coil is the non-sulphated precursor in heparin biosynthesis; K5 is composed by two components, 16000 and 1500 Da, their ratio depending on the fermentation conditions. In this study an assessment was made of how various cell-culture filtrate separation technologies affected the components themselves and their ratio. A dynamic membrane filtration technology a tubular ceramic module for tangential flow microfiltration and the standard discontinuous centrifugation were comparatively employed to perform the separation. Experiments carried out on E. coli cultures containing the two components in different ratios showed that the DMF system is a suitable technology for K5 isolation.