Emulsion Oxidation Problem

Hi there,

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:

Water Phase:
Aqua 
Oryza Sativa (Rice) Starch 
Vaccinium Vitis-Idaea (Lingonberry) Extract & Glycerin 
Gluconolactone 
Siligel 
Sodium Stearoyl Lactylate 

Oil Phase:
Glyceryl Stearate 
Isoamyl Laurate & Isoamyl Cocoate 
Safflower Seed Oil
Cetyl Alcohol
Jojoba Seed Oil
Polyglyceryl-6 Palmitate/Succinate
Mango Seed Butter
Squalane
Chamomile Flower Extract
Sunflower Seed Oil
Tocopherol
Cetearyl Alcohol

Cool Phase:
Niacinamide
Glycyrrhiza Glabra (Liquorice) Root Extract
Salix Alba (Willow bark) Leaf Extract
Potassium Sorbate

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. 

Alfie

Comments

  • PaprikPaprik Member
    Hi,

    could you at least share what the lipid portion? In total? 
    And extracts?

    When you state you add Tocopherol into Oil phase. Does that mean you are heating it with all the lipid portion for emulsification? 
    That might be the problem. Tocopherol (I am guessing you are not using Tocopherol Acetate) is heat sensitive and if you are using it in balm/hot pour, you need to increase its input significantly as some of it does oxidase due to the high temperature. 

    Also, I am not really sure about your preservation system. 
    Gluconactone does help with preservation of the product, but I would not rely on it. Especially with Potassium Sorbate only. (You have a very nutrient rich formula)
  • suswang8suswang8 Member
    I think you need to add at least one additional preservative plus 0.25% or so of  sodium phytate (chelator), and then come back to us.  
  • GraillotionGraillotion Member
    edited May 26
    You have only listed a partial preservative, that ONLY works in a given pH range...and NOT listed a pH of the product (or did I miss that in my cursory scan).

    I guess my first question is... How do you know your product is not rotting...instead of oxidizing?  I guess...I would start by using a proper preservation system, then see how things perform beyond that point.  One step at a time.
  • alfie101alfie101 Member
    edited May 26
    @Paprik - The lipid portion is approx 16%. I was told that you should add tocopherol to the oil phases for emulsification otherwise it wouldn't be in 'contact' with the phases it is trying to protect. As for the preservative system, I have tried multiple but this one has passed PET testing at the start and after one year of storage at RT.

    @suswang8 - See above as per the preservative. As for sodium phytate this is one of the options I am currently trying. Only issue is that it completely destabilised the siligel in my water phase, any idea why?


    @Graillotion - See above as per product rotting. The pH of the product is 4.7. 

    Thanks for your responses.

  • ketchitoketchito Member
    @alfie101 Some oxidation processes can be catalyzed by the presence of metal ions (some extracts have them in significant amounts), and that's why adding a chelant like GLDA makes sense. Try always having one. I'd also replace the sorbate (tends to contribute with some specific odor) by a more broad spectrum (and less allergenic) combination, like Phenoxyethanol and Sodium benzoate.
  • AbdullahAbdullah Member
    I am testing small amounts of 3 oils ( bitter almond oil, sweet almond oil and unrefined hempseed oil) for oxidation since last year to see what happens at the end.
    They are placed in Sunny window, transparent package most of the time. I am sure that they have oxidized a lot because the texture has changed and grainy things has formed specially in sweet almond oil and hempseed oil. 
    The only thing that hasn't changed at all is the smell. Bitter almond and unrefined hempseed oil has strong aroma. 
    So i think your problem is not oil oxidation.

    After how much time the smell turns bad?
    I also think it may be contamination.

    Have you tested for contamination after the smell and color change?

    If not, one simple test would be to add 0.3% EDTA liquid+ 1% DMDM hydantoin, formalin or CMI MI. If the smell changed it means it was contaminated, high load of these strong preservatives killed the microbes and now it is not contaminated, that is why bad smell has gone. 
  • alfie101alfie101 Member
    Ok, thanks for the advice everyone!
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