Rancidity happens in different ways (for the full post, click here). Anti-oxidants fight that rancidity in different ways - one might kill microbes that could cause oxidation, while others might scavenge free radicals. By combining various anti-oxidants, we can create a full spectrum anti-oxidant mixture that can help stave off rancidity in different ways.
Studies have shown that 0.05% alpha-tocopherol and 0.02% ROE combined in a water in lotion prevents rancidity for five days longer than either one alone. Alpha-tocopherol acts as a free radical scavenger, combining with free radicals to stabilize. When ROE is included with the alpha-tocopherol, it donates a hydrogen atom to regenerate the alpha-tocopherol so it can keep scavenging those radicals. When the ROE is expended, the alpha-tocopherol will keep anti-oxidizing until it is gone, then rancidity kicks in.
As a note, five days might not seem like a long time, but these studies were done subjecting the lotions to super high temperatures (170˚F, for instance) - a temperature that should ruin a lotion within a few days at the most - so it is significant.
When we combine two anti-oxidants (or more), they can work together to stave off rancidity a little longer. So combining something that is a great free radical scavenger (alpha-tocopherol) with something that protects from photo-oxidation (like the carotenoids) will boost the anti-oxidative power of each nicely.
This happens in our ingredients. In rosemary extract, the carnosic acid, carnosol, and rosmarinic acid are all hydrogen donors, while the carnosic acid and carnosol behave as chelating ingredients, binding to metal ions that might cause auto-oxidation. If we were to add ROE to sea buckthorn oil - Vitamin E is a free radical scavenger and would happily accept the donated hydrogen, and the carotenoids slows down photo-oxidation - we'd have a seriously awesome anti-oxidant combination to our lotion.
Join me for fun formulating with cucumber extract tomorrow!