[formul8101]

addition of a polyol (sorbitol, xylitol, erythritol, Glycerin) around 10% would aid in preservation by reducing water activity. Xylitol and Erythritol also have anticavity action and produce a cooling sensation in the mouth which would aid in masking the bitterness of some of the oils added. I would avoid lowering the pH below 5.5 as remineralization of tooth enamel cannot occur below 5.5.

[formul8101]

Is it necessary to have Preservative Challenge Tests done on products with physiochemical factors that would make them low risk according to ISO 29621 i.e. a pH > 10 or Aw < 0.75 ? 

[formul8101]

@MarkBroussard will Schulke still perform a free KOKO test challenge test for any formulations containing a schulke product?

[formul8101]

After further researching preservatives systems that would function under the formula conditions of toothpaste, i.e. neutral to slightly basic. I am going to try the following:

EPE 9010 0.5% (phenoxyethanol 90%, ethylhexylglycerine 10%)

1,3 propanediol 4% 

I plan to dissolve them in a separate liquid phase under high shear that I would then add as a third phase to the combined ingredients. 

[formul8101]

After reading more into preservative properties of Benzyl alcohol ( https://www.americanpharmaceuticalreview.com/Featured-Articles/38885-Antimicrobial-Preservatives-Part-Two-Choosing-a-Preservative/ )

I am wondering how it would function in a toothpaste. The pH required for Benzyl alcohol to be most effective is below 5, however, a toothpastes function requires it to be neutral or slightly basic to prevent dental carie formation. would the benzyl alcohol still function at a pH of around 8 or would this cause issues with deprotonation of the alcohol group and a subsequent loss of function? 

Also does anyone happen to know what category toothpaste is classified as under USP51? I am assuming category 3? 

[formul8101]

Thanks DAS you are completely right I got mixed up with the CFU value it is 100 which I would want to be far below. As for the preservative challenge test I will do one but after performing some of my own microbial tests on the prototype with dipsildes.

I think the formulation will end up being something like this 

Calcium Carbonate (abrasive)
Sodium Bicarbonate (neutralizing agent + abrasive)
Xylitol (sweetener + humectant)
Sorbitol (moisturizer)
Minerals 
Water 
Flavoring Oils
potassium cocoate (surfactant/emulsifier) or another non SLS surfactant
Xanthan Gum (binding agent/Thickener)
Benzyl alcohol (preservative)

I will have to investigate the preservation of the formula however I would hope that by decreasing the water content and metabolizable ingredients it may not require more preservation than the benzyl alcohol.

[formul8101]

I agree that there is nothing wrong with glycerin. That said what people perceive as ‘natural’, ‘safe’ or ‘healthy’ can affect the marketability of a product. As such I am going to experiment with not using glycerin. 

I am going to use potassium cocoate as the surfactant / emulsifier and I am thinking that I will try to reduce the water content sufficiently to prevent microbial growth through the replacement of water with coconut oil, a binding agent and potentially glycerin.

[formul8101]

Thanks for the input Gunther I will start looking into these.

I also missed castile soap in the ingredients list I provided. So that is filling the role of emulsifying agent and surfactant. That said I do like the idea of sodium cocoate or potassium cocoate. 

I also just made a small batch with the addition of some bentonite clay. the reasoning behind this was the hydrophilicity of the clay and its fine particle size might help with the binding and consistency of the product, it would also function as an additional mild abrasive. The bentonite clay did thicken the product up, however, did require the addition of more water which might pose a preservative issue. 

I might look into a coco oil or similar anhydrous formulation. I know glycerine could aid in making a anhydrous formulation, however, I am not sure whether I should avoid using it due how contentious it is for some people.

[formul8101]

Thanks for all the input guys it has been really helpful. 

[formul8101]

” 2. not necessarily - if there’s not enough water in the formula to sustain microbial growth, the product can easily pass a challenge test without an active preservative (at my last place, this was our preferred method for preserving toothpastes)

personally I’d describe that as “self-preserving” rather than “preservative free”, as it’s less ambiguous and less open to legal challenges” 

@ Bill_Toge

I have been trying to determine a water activity for a series of toothpaste I am working on that would keep their microbial activity down and effectively make them “self-preserving” as you described. What water activity would you recommend to be below in order to achieve this?

The literature I have found has implied that a water activity of less than ~ 0.9Aw.

Thanks for your time