Effect of aeration and carbon/nitrogen ratio on the molecular mass of the biodegradable polymer poly-beta-hydroxybutyrate obtained from Azotobacter chroococcum 6B
1997
Quagliano, J.C. | Miyazaki, S.S.
The bacterial polyester poly-beta-hydroxybutyrate (PRB) was quantified and characterized on an isolate of the nitrogen-fixing bacteria Azotobacter chroococcum 6B on the basis of its average molecular mass, determined from the relative viscosity at different aeration rates and carbon/nitrogen ratios during culture in fermentors. A higher value for the molecular mass (1100 kDa) was obtained with the lower aeration rates investigated, which diminished, significantly at the highest aeration rate of 2.5 vvm (a 100-fold decrease). The yield of PHB relative to the amount of glucose consumed increased with the C/N ratio (a maximum of 0.16 g PRB/g glucose consumed with a carbon/nitrogen ratio of 137.7), but the molecular mass was lowered from 800 kDa to nearly 100 kDa. The maximum PHB content was 63.5% (on a cellular dry-weight basis) after 47 h in fed-batch culture with an initial C/N ratio of 68.9 and aeration at a rate of 0.5 vvm. Calorimetric measurements on the isolated PHB showed a melting point near 175 degrees C.
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