I am attempting to formulate a face moisturiser using natural ingredients. Unfortunately I am having some issues in terms of the oxidative stability of the formula (at least I assume it is oxidation). As I have no scientific means of measuring peroxide values etc. I am relying on smell, pH and colour changes.
The formula is:
Oryza Sativa (Rice) Starch
Vaccinium Vitis-Idaea (Lingonberry) Extract & Glycerin
Sodium Stearoyl Lactylate
Isoamyl Laurate & Isoamyl Cocoate
Safflower Seed Oil
Jojoba Seed Oil
Mango Seed Butter
Chamomile Flower Extract
Sunflower Seed Oil
Glycyrrhiza Glabra (Liquorice) Root Extract
Salix Alba (Willow bark) Leaf Extract
Sadly I cant post percentages so hopefully this is sufficient without.
Originally the problem I had was with the almond smell that the formula was giving off (I was originally using Benzyl Alcohol as my preservative) but I took this out thinking that it was the cause of the issue. This did remove the almond smell but certainly not the oxidation problem. It also led me to believe that the problem is in the water phase of the formula.
The batches I make now all seem to change from a white colour to a feint brown/off white. The smell also changes, it is not overly unpleasant but definitely less pleasant than straight after I have made the batch. I have retested the pH for all of my batches as I know that Gluconolactone has a tendency to cause ph drift but the values have remained consistent over several years. I have tried running knockout tests to work out what the issue is but I just want to see if there are any parameters I am missing.
I first wondered if it was due to a lack of tocopherol. The original formula only has 0.05% but I have since produced batches with concentrations ranging from 0.2-0.5%. No luck.
I also wondered whether the lack of an effective chelate could be the issue. I thought gluconolactone would be sufficient but I have recently discovered that it is only effective at a high pH. I do have an old formula that is relatively similar in composition (thought not identical) where I used GLDA and the formula has remained very stable over the course of 3 years. Sadly this also contains green tea and has a higher viscosity so it is difficult to draw conclusions from this.
This brings me onto my next question. The formula mentioned above containing GLDA has a far higher viscosity than my current formula and as mentioned has remained very stable. I know that viscosity does have an impact on oxidation and the rate at which it takes place. If I understand correctly this is mainly due to the ability of oxidation to diffuse through the formula, if so would I be right to imagine that there would be oxidation on the surface if viscosity was the preventing factor in this case? I also wondered whether the increase concentration of emulsifiers might be 'protecting' the oil phase from interacting with dissolved oxygen in the water phase?
My final question is in terms of water soluble antioxidants. At the moment I am not using one. I have read that gluconolactone functions as an antioxidant but I assume it is nowhere near effective enough to stabilise a formula. Any suggestions on natural antioxidants that might help? I cant seem to find ergotheonine or NAC but if they are by far the best then I'm sure I could track them down.
Any thoughts on something that I might be missing would be greatly appreciated or methods to prevent oxidation that I should be considering.