Robert Tisserand replies about Vitamin-E added to slow the oxidization of essential oils:
“There are four principal isomers (chemical subtypes) of tocopherol:
There are also sub-types of each one.
You can use ‘mixed’ tocopherols: all four in various proportions. But my preference for essential oils is to use alpha-tocopherol, specifically d-alpha tocopherol…
the tocopherol should be added at 0.1% by weight of the total product. Putting more in won’t be more effective.
Although ‘tocopherol’ and ‘vitamin E’ are often used synonymously, vitamin E is actually even broader, because the term encompasses both tocopherols and tocotrienols.”