Alginate can be precipitated from culture broths by adding several solvents, such as ethanol, isopropanol, and acetone. Once the precipitate has been washed, it can be dried and gravimetrically determined. In this work, the following procedure is used:
1. Add 3 vol of ice-cold 95% ethanol to 1 vol of culture broth at 4°C into preweighed tubes, stirring slowly.
2. Centrifuge the mixture at 12,000^ at 4°C for 10 min.
3. Remove the supernatant carefully.
4. Resuspend the gel-like residue in 1 vol of distilled water.
5. Add 3 vol of ice-cold 95% ethanol, stirring slowly.
6. Centrifuge the new mixture in pre-weighed tubes at 12,000g- at 4°C for 10 min.
7. Remove the supernatant carefully.
8. Dry the tubes in the oven at 105°C for 24 h and determine the alginate dry weight and concentration (P).
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