Lotion bars: Tweaking the waxes, Tracy asks: I was wondering if it would be okay to add an antioxidant like ROE or Vitamin E T-50 to extend the life of the oils? If so, does it matter which one is used?
Yes, you can add anti-oxidants to any oil soluble product to extend its life span. Rosemary oleo resin, Vitamin E, and some essential oils are all good anti-oxidants. Use them at the usage levels suggested by your supplier.
Frequently asked questions section of the blog
A more in-depth look at anti-oxidants
How do anti-oxidants affect the shelf life of our products?
Rancidity: A primer
More questions about preservatives!, Michele J asks: Rocky Mountain Soap claims their products are 100% natural. I questioned them on preservatives and they said their lotions contain either Vitamin E or Basil Oil (sodium levulinate) as the preservative. They also claim their lotions have been tested and are fine for up to one year. What are your thoughts on this?
Vitamin E isn't a preservative; it's an anti-oxidant. It retards rancidity in our oils and butters, which isn't the same as preventing microbial contamination by yeast, bacteria, or fungus. It's a great inclusion in a product that contains oil soluble ingredients, but if someone is saying it's a preservative, they are wrong.
As for sodium levulinate (aka sodium 4-oxovalerate) - I think it's a bit disingenuous to say it's "basil oil". It might be derived from basil, but that's like saying that behentrimonium methosulfate (BTMS) is colza or rapeseed oil. Would I consider it natural? No. There are so many processes between pulling the basil from the soil to becoming sodium levulinate that I think one would have to be straining to do some explanining to call this natural. If this is natural, then almost every ingredient we use is natural as they are all derived from some natural ingredient in the beginning.
I found this reference from Perry Romanowski of the Chemist's Corner that it isn't enough to preserve a product on its own (link, scroll down or search on the page), so it needs to be combined with something else to be a broad spectrum preservative. I found it with potassium sorbate in Verstatil SL and with sodium anistate in Dermosoft 1338. Considering that Rocky Mountain Soaps also has sodium anisate in their lotions, it seems like they're using this version, which would be effective against gram+ and gram- bacteria, yeast, and mold.
As an aside, this book notes that sodium levulinate might work as an anti-freeze. Considering that things that might work as anti-freezes are considered evil by places like EWG - "propylene glycol is found in anti-freeze!" - what does it mean for this preservative?
As an aside, it looks like they are using glyceryl stearate and quillaja saponaria as emulsifiers? (Read more in this post about the use of these surfactants for foaming products.)
What do I think? I think they are using a broad spectrum preservative that contains sodium levulinate and sodium anistate that might good for a year. (It'll depend upon the oils they're using, too.) They are using an anti-oxidant in the form of Vitamin E, which will help retard the rancidity of oils (although I didn't see it in their water containing products, like this one.) To say their products are 100% natural - that would be a matter for debate.
Preservatives: How do they work?
Join me tomorrow for more comment-y fun!