Surfactant Oxidation with sorbates and benzoates

Does anyone observed oxidation or stability issues when combining Sodium cocoyl glutamate, Sodium Lauroamphoacetate (surfactant base) with Potassium sorbate and sodium Benzoate preservative syst. for hand soap application.  After a week in accelerated stability the solution turns clear yellow and and 2nd to 3rd week turns clear orange, and develops a sweet aroma.  
I suspected the potassium sorbate had an effect on this reaction but i starting to believe that could be the other way around.  The sorbate moiety has two double bonds prone to oxidation. 


  • Are you adjusting pH in this? those surfactants have a higher pH, and your preservative system is useless above pH 5.5-6. If you do go that low your surfactants might have issues though
  • pH 5 to 5.5

  • Bill_TogeBill_Toge Member, Professional Chemist
    this is a well-known 'feature' of sorbate salts in water-based products; they're best suited to dry/hygroscopic products
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • Adding citric acid/sodium citrate helps with sorbic acid oxidation 
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