We are trying to quantification EPS in sourdough. We follow the bibliography protocols: We centifugate the sample, then the clear supernatant was collected, and the EPS was precipitated by adding ethanol overnight. The precipitate was recovered by centrifugation and dissolved in distilled water. At this point we have the problem that the solution is not dissolved well and it is turbid. How we can obtain a clear dissolution with out pellet?
I presume you've tried heating the suspension; that might work. It is possible that you have more than one polysaccharide. If it were me, I would check to see if the turbidity was due to starch polysaccharides. A simple iodine test would probably suffice. If it is starch, then you will probably want to eliminate it prior to working up the EPS. It sounds like centrifugation would accomplish that; if not, perhaps amylase digestion would work. If it's not starch, then you can still separate it from the clear supernate and work it up separately. Adjusting the pH upward with NaOH might dissolve it. You can, of course, simply do a phenol-sulfuric acid analysis on the turbid suspension, but that would not give you the most useful or reliable information.
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