Enhancement of extracellular polymeric substances (EPS) production in Spirulina (Arthrospira sp.) by two-step cultivation process and partial characterization of their polysaccharidic moiety

The interactive effects of light intensity and NaCl concentration were investigated for Spirulina two-step cultivation process using Full Factorial Design. In the experiment interval, light intensity had no effect while the NaCl concentration had significant effect on the enhancement of extracellular polymeric substances (EPS) production. Interestingly, results revealed a significant negative interaction between light and NaCl concentration indicating that high NaCl concentration (40 gL−1) and low light intensity (10 μmol photons m−2s−1) enhanced the EPS production. Under these conditions, EPS production reached a maximum of 1.02 g g−1 of biomass (dry weight), which is 1.67-folds greater than EPS content under optimal growth conditions (10 μmol photons m−2s−1, 1 g L−1, 30 °C). Desalting and deproteinezation steps of EPS were efficient to obtain polysaccharides (PS) with high carbohydrate (67.3 ± 1.1%), low soluble proteins (5.14 ± 0.32%), ash (5.85 ± 0.71%) and sulfate (2.42 ± 0.12%) contents. Rheological studies of PS at different concentrations (1%, 2.5% and 5%) revealed that the viscosity of the solution increased with the increase of PS concentration. In addition, PS exhibited a non Newtonian shear-thinning nature, a predominant gel-like behavior and a good resistance to consecutive heating-cooling cycles. The adopted process could be, then, a promising and economic strategy to enhance EPS production and extract polysaccharides with interesting rheological properties.