As a consequence, some preliminary rheological measurements in the ranges of native concentrations (Table 3) of polysaccharide in distilled water were conducted. Flow properties of the more significant concentrations are reported in Fig. 7. No significant differences appeared between flows of the polymers extracted from R. violacea and P. purpureum whereas strong differences were detected between those extracted from A. platensis and those coming from red microalgae. The Cross model applied to these results (Table 3) indicates that the ‘zero shear’ viscosity (i.e., η₀) of polysaccharides from A. platensis was inferior to these of the two red microalgae in water with a factor of 20 for the 1.5 g l⁻¹ concentration. Even if this difference decreased for lower concentrations, it remained significant showing that the BFI decrease was in correlation with the increase of viscosity in culture media of red microalgae. Interestingly, the presence of non viscous high-molecular-weight exopolymers as these produced by the strain of A. platensis used in this study was not sufficient to obtain BFI <2.