Does anyone have ideas how to remove calcium from defatted fish bones (other than using pH changes?). The product should stay food-grade.
I assume the calcium is in hydroxyapatite form and partially bound to collagen.
Any input would be greatly appreciated.
EDTA will certainly do the trick, but "food grade" suggests your bones are going to be eaten (yum yum!). I'm not sure if EDTA is allowed. However acetic acid in the form of "spirit vinegar" will work equally well and is much quicker. Not sure what the objection to low pH is; this could be raised again as soon as the calcium has been solubilised.
Thank you for your answer. The pH is the best (read: simplest) way to go, however, depending on what you put in, once you neutralize the pH with a base, you will also have to remove the possible (NaCl / acetate / etc). This is actually why cheap 'soy' sauce is salty (they use the HCl to hydrolyze the protein and then is it neutralized by NaOH). However, if you would like to reduce the waste water and the amount of aqueous processing steps, then you get stuck with my problem.
Not sure whether the answer is still relevant, but you could use food grade phosphoric acid to solubilise the bone minerals / apatite phases, and then precipitate most of the phosphates and calcium using calcium hydroxide. There are some micro-minerals that also get solubilised from the bones though, and which will not necessarily precipitate.
Thanks for your input. Phosphoric acid is indeed a good method to solubilize the apatite, however I think this would affect the protein characteristics. Perhaps I can find a concentration at which the effects will be minimized. thanks again.
There is an electrolytic process for decalcification of bones. Not sure of the details but it might be worth looking into as pH would not be changed. Regarding acid decalcification, I routinely use 6M trichloroacetic acid which is a very gentle agent; however, this is on aldehyde-fixed bones. Neutralising with alkali is simple. If you're worried about losing material, then do the whole procedure in a dialysis bag.
Hope this might be some help.
Simon
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