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Sodium benzoate in toothpaste
How does 0.3% (or around there) sodium benzoate actually work in toothpaste, since toothpaste should be a neutral pH?
I thought sodium benzoate is most effective at pH 4 or less (or an acidic pH that a toothpaste would NOT be at).
Thanks for your time in answering!
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7 Replies
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With some surfactants, the effective pKa of benzoate is increased making it effective at higher pH.
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I’ve been developing toothpastes for a few years now. Most of our toothpaste does not use any sodium benzoate, potassium sorbate or any other preservative; however two of them do - our toothpaste is stable based on low water activity (0.2 from memory), high pH (calcium carbonate pastes are generally pH 8-8.5).
We have tested to various PET/Log count methods (ISO, BP, USP etc) and all passed with the exception of the kids toothpaste.
With the kids toothpaste we sought extra advice on pH from Indiana University’s Oral Health Research Institute as to the lowest pH we could go to - and the advise we received was surprisingly low; however, we ended up using potassium sorbate and targeting a pH of 5-5.5 and we passed PET/Log counts.
Note: We develop to a natural standard and many options for effective preservation were not available to us.
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Surfactant micelles cause increased concentration of the ionic moiety (undissociated active) of the SB in the water/phase which can, depending upon the type and concentration of the SAA alter the PKa. The value of the latter has to be determined by experiment
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One can see the impact in challenge test results - with the right challenge test resukts.
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correction …… with the right challenge test.
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Would this be true for any of the organic acids to some extent?
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Not aware such data exists for others.
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