Effect of extraction temperature on the diffusion coefficient of polysaccharides from Spirulina and the optimal separation method

The extraction temperature had a significant impact on the concentration of polysaccharides derived from solid-liquid extraction of Spirulina. The polysaccharide concentration was significantly higher when the extraction was performed at 90A degrees C than when it was performed at 80, 70, and 50A degrees C. This result is related to the diffusion coefficients of the polysaccharides, which increased from 1.07 x 10(-12) at 50A degrees C to 3.02 x 10(-12) m(2)/sec at 90A degrees C. Using the Arrhenius equation, the pre-exponential factor (D (0) ) and the activation energy (E (a) ) for Spirulina polysaccharide extraction were calculated as 7.958 x 10(-9) m(2)/sec and 24.0 kJ/mol, respectively. Among the methods used for the separation of Spirulina polysaccharides, cetyltrimethylammonium bromide (CTAB, method I) and organic solvent (ethanol, in methods II and III) provided similar yields of polysaccharides. However, the separation of polysaccharides using an ultrafiltration (UF) process (method III) and ethanol precipitation was superior to separation via CTAB or vacuum rotary evaporation (method II). The use of a membrane with a molecular weight cut-off (MWCO) of 30 kDa and an area of 0.01 m(2) at a feed pressure of 103 kPa with a mean permeate flux of 39.3 L/m(2)/h and a retention rate of 95% was optimal for the UF process. The addition of two volumes (v/v) of ethanol, which gave a total polysaccharide content of approximately 4% dry weight, was found to be most suitable for polysaccharide precipitation. The results of a Sepharose 6B column separation showed that the molecular weights of the polysaccharides in fractions I and II were 212 and 12.6 kDa, respectively.