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Bacteria in Glycerin Containing Product?
My company has a product that contains glycerin, it’s not a cosmetic, it’s a paint booth coating. I was looking at a retain sample from September and I noticed something I think is bacterial growth- it’s like a fuzzy greyish spot with a darker spot in the center. It’s very small, less than a centimeter in diameter. Is this bacteria? I know glycerin is a sugar so maybe bacteria could grow in it?
Water 57.40%
Glycerin USP 39.3%
Acrysol TT-61 52.65%
Triethanolamine 0.65%
We don’t use deionized water, do you think that could be the issue?
Thanks for reading
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10 Replies
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Got to be either bacterial or a fungus such as yeast. Take it to a microbiology lab and have it identified. You don’t have any preservative in that list!
Your LOI adds up to around 150% by the way. -
Supposed to be 2.65% Acrysol! Sorry! Poor proofreading on my part. Thank you for your expertise Belassi. Can you recommend a preservative I could try?
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You’ll definitely have to use a preservative in that. I know some people think glycerin ‘helps’ preserve things, but in my experience, not.
The preservative you use will depend largely on your location and I am not sure where you’re based. Since this is by definition not for human use, a large number of possible preservatives could be considered. I only know about cosmetic preservatives - I suspect there are a large number of low cost preservatives you could choose rather than those approved for human use. -
Personally, I’d use Kathon CG.
Did you send the product out for a micro test? -
You could contact your Dow representative and ask what they recommend since you are getting the Acrysol from them.
I would recommend investigating a benzisothiazolinone preservative (such as Proxel GXL) as these are usually recommended for coatings and are stable over a wide pH range. What pH is your product?
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You can preserve with a glycol but you really need to do testing such as Micro and Water activity (Aw). Every text is quite adamant that you can not extrapolate the Aw. A few years ago I was sat at an SCC Dinner with several chemists from a company where they preserve with Aw. It was difficult and they measure Aw not just in the lab but also as a QC Check on the floor. All this for a “preservative free” claim. For me it is way more than one needs to do. Just use the correct preservative and do the micro. No shortcuts there.
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The other “preservative” I’ve used for HI&I products is Dowicil QK-20, but it’s really more of a chemical sterilizer - it breaks down completely within 24 hours, so there is no consumer safety issue.
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Sounds more like fungi to me (likely Aspergillus sp.). Is it on top of the product or submerged?
Cause theoretically, glycerol (which isn’t a sugar but a polyol) above 20% is self-preservative but this does not count for surfaces where mould can thrive because it ‘floats’ on the product and doesn’t touch it enough to succumb to the osmotic pressure which is the main reason for the self-preservation. I’ve seen Aspergillus and co. growing on the weirdest places and preserving a surface isn’t as easy as the interior; why exactly it chose your product as growing medium I do not know. Adding a chelate (e.g. EDTA) can help reducing available microbial food (mostly iron) which is more abundant in technical grade products than in cosmetics or use a formaldehyde builder or a quat. I don’t like these two very much in cosmetics but they work usually better against surface contamination than the more ‘natural’ ones like parabens, benzoate, sorbate etc. -
Great insight @Pharma.
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Since glycerol isn’t a sugar but a sugar alcohol, it can’t be fermented, which means the organism using it for food must obtain oxygen. Note that the fungus was on the surface, where it not only doesn’t feel the full osmotic pressure of the glycerol, but also could get oxygen from air. The better you can exclude oxygen from your container, the easier it’ll be to preserve. You might even be able to preserve the solution with a reducing agent such as a sulfite.
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