Total aerobic count in wax/oil cosmetic - (Aug/09/2022 )
Hello everyone! I'm hoping somebody can help shed some light on a project I've inherited. My company is a contract manufacturer in the cosmetics business specializing in wax/oil based lip balms and deodorants. One of our largest customers requires us to determine the total aerobic count in every lot of their products that we produce. Our R&D chemist has conducted that test ever since this customer contracted with us, however, he is now retiring and the micro side of finished product testing is falling to me. Our current method is to weigh out 10g of product and 5g Tween 20 into a sterile plastic cup and mash into a homogenous slurry. That slurry is added to 90mL of Butterfield Buffer and shaken. 1mL of this new mixture is added to 3M AC petrifilm and incubated. My concerns are that the product/Tween slurry is not truly homogenous, and even if it is, it does not incorporate very well at all in the 90mL of buffer. At the end of shaking there is a big mass of product floating at the top. I want to know if there is a better way to prepare a wax/oil product prior to plating because it does not seem likely that any bacterial present would be released from the product and into the buffer. Just an FYI, my education and career so far have been almost entirely analytical chemistry. I have had a little experience with microbiological testing, but only enough to make me somewhat less of a square peg in a round hole. Any tips or advice anyone has to offer would be greatly appreciated. Thank you!
When you plate, do you plate just the buffer layer or do you plate the whole “mess”?
it seems to me that the purpose of the shaking is to extract the bacteria into the buffer.
As a chemist, you should be familiar with partitioning and extraction techniques. This procedure appears to be similar
We plate the buffer layer. I agree that the shaking is to extract the bacteria, but our current method does not allow the product/Tween slurry to become a solution or even a fine suspension in the buffer. All the shaking in the world won't extract any bacteria if the product won't break apart in the buffer, and I'm not sure how much Tween 20 I can use before I risk possibly impacting results. As for extraction techniques, most of the procedures I know are going to be anti-microbial in nature due to solvents or temperature. If our procedure is as good as it gets for this kind of product, I guess I can live with that, but there just seems to be a lot of opportunity for improvement.
If you were to add enough surfactant to homogenize the mixture then you would probably kill the bacteria.
you might be able to improve the extraction by homogenizing in a Dounce homogenizer (with the looser pestle). However, this will become cumbersome for more than a few samples.
Tried isopropyl myristate? Also try heating to ~40C max. Purpose of shaking is to emulsify /suspend - not "extract" bacteria.
Did your predecessor validate/demonstrate suitability?
Maybe consider selling your customer on parametric release. Has to be a hot fill and assuming you've got raw materials in control, think testing is wasting your time and their $.
A Douncer might be worth a shot, and at this point I think I need to introduce some mechanical means of mixing instead of just shaking by hand. Isopropyl myristate is a great solvent for waxes and oils, and it is in some of our formulas as a very low level ingredient, but is there any chance it might kill off some of the bacteria? As for suitability, my predecessor did demonstrate the method several times with different products. He swore by this method, but I have a hard time believing in it's suitability when there is still a lumpy mass of product floating in 90mL of buffer. He he never showed me any validation data either.
Our manufacturing process does involve combining, melting and mixing of all raw materials at temperatures 160-180F, so I can't imagine that there would be anything left alive by the time the bulk material is filled into containers. There are a few raw materials that have naturally high bioburdens, but our customers require them to be irradiated prior to us. I would be absolutely thrilled to finally convince this customer that micro testing is unnecessary for their products, but after all these years they still require it even though their reasons have not been made clear to me.
For mechanical, maybe try a stomacher.
Isopropyl myristate is recommended in USP 61. Think you'll be ok with it .- but try suitability and see.
I'm with you, doubt it really works. Bet he added bugs to the "suspension" and that is obviously not addressing bugs in the original wax. Anyway, if there's no documentation - it never happened.
Can't you guys make a proposal to the customer? It seems profoundly reasonable and they ought to appreciate the technical perspective and initiative even if they haven't the guts to go for it. I would offer the proposal as a process - each release is conducted with a check that temperature was reached and each raw was low/no risk or gamma'd.
We have proposed that exact thing in the same manner with no luck. I see that isopropyl myristate is recommended for "fatty products" under <61>, which leads me to a fundamental question: what should we consider our products? My predecessor has always treated our products as if they were "non-fatty products insoluble in water", and they are certainly insoluble in water. However, even though some of our products contain a majority hydrocarbon wax, all of our product contain at least 20% plant oils, triglycerides, or "fats". Most of our products are 80% fats or more. Should we be treating our products as "fatty products"?
Not sure the classification that important vs.whatever works.
Looks like I have some experimentation to do. I've done a little work with isopropyl myristate already and immediately I have a better looking emulsion than what we get using Tween 20. With a little fine tuning I'm sure I can make that work. This has been very helpful, thank you so much!