Optimization of the culture medium using the Burman and Box-Behnken experimental designs for an enhanced production of alginate by Azotobacter vinelandii

Alginates are regarded as high-value biomacromolecules. A pursuit for new bacterial species that can produce novel alginates for various applications in different industries including the pharmaceutical and food industries as well as the field of medicine is still needed. Variations in the molecular weight and sugar composition of alginates depend on the culture medium composition and different physical conditions provided during fermentation. The aim of this study was to obtain a maximum alginate production by the potent Egyptian bacterial strain Azotobacter vinelandii , out of the 30 tested Azotobacter isolates. The composition of the production medium and environmental growth conditions during fermentation were optimized to ensure consistency and to enhance alginate production. Nine variables were optimized using the Plackett-Burman randomization method. Eighteen trials were performed to verify the variables to obtain high alginate production levels. Temperature as well as sucrose and NaCl concentrations have been found to affect the alginate production by A. vinelandii significantly and were therefore chosen for further improvement of the medium using the Box-Behnken design. The Box-Behnken model was optimized mathematically using the Excel solver. The results were analyzed statistically by ANOVA multiple regression analysis and different statistical methods (coefficient, standard error, t statistic, and confidence interval). On using the Plackett-Burman and Box-Behnken designs, the biggest alginate production rates were found to be 3.8 and 4.94 g/l/day, respectively. Addition of 00.1 g/l MgSO4, 0.01 g/l FSO4, and 0.001 g/l NaMoO4 to the culture medium further enhanced the alginate production and yielded 5.4 g/l/day and 8.5 g/l/day. Thus, the obtained alginate was purified using Sephadex G-100 Gel chromatography and compared with a standard by IR correlation. The alginate was found to be composed of 50–70% carbohydrates and 60–80% uronic acid. The techniques used in this survey were found useful for improving the production of alginates.