Leucidal: Radish Root Ferment Filtrate.
AMTcide: Lactobacillus & Cocos Nucifera Fruit Extract.
These ingredients are both for sale here in Australia at New Directions and there is a bit more information about them on the website as to their chemistry and manufacturing instructions here and here.
The above preservative pairing may be attractive to those with a brief to product a product that is:
But don't get too excited because the above pair may not be good for those with a brief to produce a product that is:
So, now we've got that cleared up let's explain the plan.
I wanted to come up with a simple, but not too simple, cream that we could use as a base - not a 'nothing' base but a base that would be fairy well representative of what a customer might start out with. A daily moisturiser with medium viscosity and intensity. Here it is:
Soothing Moisturiser for Dry and Damaged Skin
|Acacia and Xanthan Gum||0.50||Tickener and gives the serum staying-power on the skin|
|Glycerin||5.00||Humectant to stop cream from drying out and also as a moisturising active|
|II||Caprylic Capric Triglyceride||8.00||Light weight emollient for skin feel|
|Camellia Oil (Organic)||6.00||Light weight, low allergy oil for moisturisation without clogging|
|Emulsifying Wax SGC (Glyceryl Stearate (and) Cetearyl Alcohol (and) Sodium Stearoyl Lactylate)||3.00||Emulsifier|
|III||Liquid Extract Green Tea Water Based||3.00||Active for soothing and moisturising skin|
|AMTcide (Lactobacillus & Cocos Nucifera Fruit Extract)||2.00||Anti-microbial but particularly strong against Fungi.|
|Leucidal (Leuconostoc/Radish Root Ferment Filtrate)||2.00||Broad Spectrum anti-microbial protection|
As you can see this is a simple cream, naturally derived. The water phase contains a thickener (Acadia and xanthan Gum) to help build viscosity and also stability, especially freeze/thaw stability and glycerin - at high level in this cream, this is to bind moisture to the skin and also to maintain a cushiony texture over time - cetearyl alcohol heavy creams can dry out over time. The oil phase contains just an ester (fractionated coconut oil type, light skin feeling, non greasy), Organic Camellia oil - another lovely oil for the skin and especially for facial care as it is so soft and light and then there is the emulsifier and emulsion stabiliser/ thickener (cetearyl alcohol). The oil phase in this cream is quite substantial (albeit simple) and so the emulsion will contain plenty of nutrition for microbes without being ridiculously impossible to preserve. I added a liquid (as in water based) extract to just add a bit of micro-drama into the product. This green tea extract contains Water, Alcohol, Camellia Sinensis Leaf Extract, Xanthan Gum, Potassium Sorbate, Citric Acid - so it is preserved as-is but may still increase the microbial stress on the formula, especially given it is there at 3%. Finally the preservatives were added which, in this case was 2% of each of the Leucidal and AMT Cide. You may notice that I have not added a chelating agent into this formula. I usually put chelating agents into everything but didn't want to 'help' the preservative out in this case. Adding something like EDTA, EDDS or Sodium Phytate would be a worthwhile thing to do, especially if you were looking to add more challenging actives into your base cream. Finally I opted to settle on a pH of 5-5.5 for this cream so as to be skin friendly. This pH is trickier to preserve than a pH of 4-4.5, which is slightly more extreme and unfavourable for some microbes so I could have helped myself by lowering the pH slightly - that is a strategy I could try should this product fail PET.
Good Manufacturing Practice can be the difference between a pass or fail but your manufacturing process has to be realistic and to be honest that does not need to mean 'operating theatre' standard. It is important to use clean water -I used demineralised, and I made sure my ingredient stock was relatively fresh. It is also advisable to wear a lab coat (to prevent your sleaves etc getting in the cream or bits of dust from your clothes), gloves and a hair net if you have lots of hair. I didn't do that this time but if I was making this product commercially I sure would. Finally I packed the cream into a glass bottle that had come out of a full box - I didn't pre-sterilise it though so it was only as good as it left the glass bottle factory.
For a Preservative Efficacy Test around 100g of product is needed. The test runs for 28 days and during that time the moisturiser is 'challenged' by having a known amount and type of microbe added to it at. The product is then measured at 7, 14 and 28 days to see how it is fairing. The speed at which it cleans up this micro soup mess is important and ideally the cream will meet every 'challenge' with glee and keep the cream and its user safe. The idea behind this is to emulate what could happen in-use with people putting their hands into the container repeated times. A challenge test should be challenging so it introduces quite a bit more 'dirt' than you might usually find during use over a typical use period. If you want more info on PET I wrote the blurb on the New Directions site so you can check that out.
The first thing to note with these results is the Initial TVC - this is the initial micro count. You can send your product off for a micro count and you would get a report with just that top bit. This basically confirms whether your product starts off clean or not. If the product is too dirty to start with it may already be 'out of spec' for micro and not make it to PET. For a cosmetic of general use we need the TVC to be under 1000 and for the product to contain no pathogens. This product meets that by a mile having counts in all categories of less than 10.
The second thing to look at now is the table with data for 0, 7, 14 and 28 days. This is the challenge part. As you can see different microbes are added into the cream at the start and their numbers are recorded. Ideally a product will quickly knock out all threats leaving a very clean product almost immediately but as you can see here, while the product complied it did take a bit of a while to get to grips with the A Brasillensis and C.Albicans. This result with regards to these microbes is why, in the beginning I cautioned people about using this in a more challenging formula. These more natural preservatives are typically quite slow to act as they rely on either starving the microbes, crowding them out with their 'good' bacteria or by acidifying their environment to make it more hostile to microbes. I like to think of these natural preservatives as being a bit passive-aggressive. Imagine you are at a party and the host wants to go to bed but people are still drinking and partying. The host could either a) quietly squirrel away the alcohol, turn the music down and start cleaning up or b) grab a baseball bat, stand on the table and shout 'if you don't all leave now I'll smash something'. These preservatives are doing strategy a. Now strategy a works well for polite and gentle people but not all microbes are polite and gentle, some are the micro equivalent of a criminal gang and violence is all they understand. Bringing that back to a cosmetic situation a challenging formula such as one that contains clays, other minerals and plant matter probably does require a more direct and faster response save the situation turning into a nightmare.
The last thing to note here is that the above product didn't end up as clean as it started. We started with a TVC <10 for everything but ended up with a A brasillensis count of 550 CFU/g. This is still OK for a body product but I'd want it to work a bit better if we wanted to market this product for babies, people with eczema or for an eye cream. In any of these scenarios the micro result might still be appropriate if we are going to package this product in a way that avoids such an insult but if we are going for a jar, we should really look to bolster our micro protection to save the product becoming overwhelmed in a worse-case-scenario.
The take-home message.
These 'gentle' and food-like preservative systems can and do work but that they aren't as robust as some other options and as such it is always important to run some tests on your finished products just to make sure you are covered. On top of that, using additional supporting strategies such as adding a chelating agent, using good manufacturing practice, smart packaging choices, lower pH etc can help you meet your goal.
Hopefully this worked example will help you see why we (chemists and manufacturers) worry when clients ONLY want to use nice sounding, food-type preservatives across their whole range - that strategy is unlikely to work for everything and over time it does run the risk of leaving your factory open to 'house microbes' that evolve strategies to resist your gentle anti-microbial strategy. This can end very badly.
Overall it is great that these days you can preserve your product with 'nice' sounding ingredients that actually work and lovely that we now have so many pleasant options available to us but mostly it is wonderful that a simple test like this can tell you so much - albeit at a cost (which is more of an investment really).
One test does not an experiment make but it is a starting point and with that I'll leave you to go off and run some tests of your own. Remember, in the world of cosmetic science, it is better and safer to weave your narrative around fact, not fiction and certainly not fear.
PS: I should also mention that there are different test methodologies available to the cosmetic chemist. We opt for the ISO 11930:2012 method as it was developed specifically for cosmetics rather than a pharmacopea method which, in many cases is over-the-top in terms of required endpoints. That said, it might be worth opting for a stricter test if you are making products for vulnerable people. I should also mention that it is highly recommended that you run your PET at the beginning and towards the end of your shelf life as a minimum. It is important that the preservative stays active for the whole shelf-life of the product and that you have evidence to prove that. A micro count at the end of shelf-life is better than nothing and is a bare-minimum starting point. Again the risks rise relative to other choices you make including packaging, pH and pack size.
26 September 2017