Of all the things I do in my work, stability testing teaches me the most and that’s why I find it a shame when companies don’t really want to pay for it to be done properly, such a wasted opportunity. Anyway, it was one such experience that highlighted an issue to me, an issue that I’ve seen to varying degrees over a range of organic products.
I got the above picture from here as I really like the way they have explained the Kombucha process and thought you might like that too!
The pH of Organic Products often shifts downwards over time but not always to a point that one would consider alarming. Why is that?
Some organic (and some non-organic) emulsion based products get gassy and thin at the same time when they degrade? Why is that?
I’ve got my theories, they are based on observations of stability test results and trends carried out over several years (I’ve been running a stability lab since 2011).
My theory is one of fermentation and it goes something like this.
Fermentation works well when the following conditions are met:
- Sugar is present, specifically monosaccharides.
- The pH is acidic, pH 4-4.5 is good.
- The formula is potentially under-preserved for the conditions. Not necessarily enough to warrant a PET fail but enough to allow some ‘good’ bacteria and especially yeast to thrive.
I see these conditions quite often in organic and some natural formulations, mainly because these are most likely to include a large amount of Aloe in the water phase (to increase the organic percentage while at the same time capturing the benefits of this sugar-rich juice).
So as extracts go Aloe derives almost all of its benefits from sugars both monosaccharides (simple sugars) and polysaccharides (complex sugars of the type found in cellulose). The natural abundance of these simple sugars makes it a prime candidate for fermentation, a process that requires the presence of glucose and simple sugars to commence.
Fermentation but first glycolysis.
Glycolysis is a potential first step in this two-step reaction and is where the sugars in the product are broken down to form Pyruvic acid which then goes on to catalyse the fermentation reaction.
This part of the reaction is as far as I think most cosmetic products get as to start fermenting a few more conditions are required. But this part of the reaction is enough to account for an ever decreasing pH.
Pyruvic acid has a very low pKa which means it could potentially see the pH of the product drop to 2.5 if it was able to build up to high enough levels. I’d suspect this was happening in any product that displayed a consistent drop in pH throughout the stability testing where no other contributing factors were present (dehydration, concentrating the acids etc).
This reaction doesn’t generate any gas so the product would look and feel as per the control until the pH dropped below 3.5 ish or was applied on damaged skin.
My worry with products displaying this type of action is that the pH drop might cause the product to become irritating over its shelf life due to this low pH. How much the pH was felt on the skin would depend on how much Pyruvic acid was produced and the ratio of the oil and water phase but needless to say it could get messy.
If you were to have a product that was thickened only by these susceptible polysaccharides you could end up with a very thin product. We often see this with Hyaluronic Acid gels (predominantly disaccharides to start with) and it certainly happens with pure Aloe gels or gels created using guar – some sugars are more resistant to glycolysis than others.
But some products don’t stop there.
After glycolysis comes fermentation and this is what generates the bubbles.
Fermentation takes the pyruvic acid as it moves to create alcohol. In doing so Carbon Dioxide gas is produced which can make a product look very bubbly.
A consequence of the pyruvic acid being used up in the fermentation process means the pH slide is halted as fermentation tends to produce acids with a higher pKa so it is more likely to end up with a product with a pH around 3.5-3.8 which is still low but nowhere near as low and irritating as 2.5 which is classed as too low for a commercial cosmetic product.
So what can be done about this?
While it is likely that this type of degradation is somewhat inevitable in this type of formula the question is can we slow it down and meet a reasonable shelf life? I think we can. Organic products are often preserved using more gentle microbiostatics rather than microbiocidals. To illustrate the difference I’ll give you the example of my cockroach problem at home. A cockroach happened to walk its self into my pantry moth sticky trap on Wednesday and while it couldn’t get off because its feet were stuck, it did eventually die – after 2 days – and that’s called a humane trap….. Contrast that with the cockroach that got a whiff of my national parks friendly creepy bug spray and died within minutes. A microbiostatic stops bugs in their tracks so they can’t feed or breed and eventually die of boredom I suppose – it would be quite boring not being able to do those things. A microbiocidal basically nukes the hell out of the bugs, killing them quickly but potentially being more toxic to the surrounds. So organic products with their more humane preservatives are an easy target for yeast – even good yeast- to start the fermenting process. Organic products are less likely to use chelating agents (in my experience here, this is probably not the case overseas) as they don’t want to use anything that reduces the organic content. A chelating agent can really help boost preservative efficacy and would be helpful here. Starting pH in some organic formulations is low due to the desire to make the preservatives work better and the fact that natural preservatives often work by acidifying their environment. A move from pH 4.5 to 5.5 might be just enough to stack the odds in your favour without ruining your preservatives life. I am sure there are more things that could be tried too but the preservative free hurdle technology is going to be less helpful in this type of formula as the presence of sugars is the start and end of the problem, not how much free water you have, especially give the fact that irradiation is banned for organic products so some microbes including yeasts are bound to be in your product to start with.
How do I find out if I’m affected by this Kombucha affliction?
Stability testing is the way to go, organised multi-temperature stability testing over a period of at least 12 weeks.
And could anything else cause these symptoms or are you sure its fermentation?
Well as I said at the beginning this is a theory so there could well be other things at play but the observations I have made across a number of products do seem to stack up with these well-known and well documented processes. Having said that products can become bubbly through other things too and viscosity can drop in gels for other reasons so it is more that the whole picture is pointing me to this conclusion than any single sign.
And is there any analytical test that could back this theory up?
That is what I’m currently looking into as I’m as keen as anyone to get some data to back this up. I can’t see why levels of Pyruvic acid, lactic or acetic acid or alcohol can’t be measured. That should be easy. Oh and of course we can do another micro test to see how the yeast levels are looking compared to at the start of the testing.
To be honest I’m not sure what I’m going to do next with this but if I do invest in some more testing I’ll be sure to let you know!