What does rosemary extract do?
Rosemary oleoresin extract (also called ROE or rosemary extract) is good at lengthening the shelf life of fats or products that contain fats. (6)
The process of rancidity begins when fat begins to oxidize -- to react with oxygen. An antioxidant like ROE protects the fat from oxidizing, because it reacts with oxygen more easily and quickly than the fat.
How is ROE used?
ROE is a dark, thick liquid with a distinct "herby" odor in the bottle.
It can be added in tiny amounts directly to pure fats or added to soaps and other bath and beauty products that contain fats.
If you want to add ROE to lotions, salves, balms, scrubs, etc., be aware the odor may be detectable in these products. Choose fragrances that compliment the odor of ROE, or look for a supplier that sells deodorized rosemary extract.
ROE is so diluted in soap, you cannot smell it.
Can I use Rosemary essential oil rather than ROE?
Until further research proves otherwise, the answer is no. Rosemary essential oil (EO) does indeed have antioxidant properties, but it is unknown whether rosemary EO is as effective as ROE for long-term preservation of fats.
One study reported "...Carnosol and carnosic acid have been suggested to account for over 90% of the antioxidant properties of rosemary extract....." (1) Rosmarinic acid may also contribute to the antioxidant properties. (5) These chemicals are not present in rosemary essential oil (2), but they are present in ROE.
Why are rosemary EO and ROE different?
Even though the EO and ROE are made from the same parts of the rosemary plant, they contain quite different blends of chemicals due to the way each is made.
Rosemary EO is made by steam distillation. Steam distillation removes only the lightest volatile chemicals in the plant material -- the aromatic chemicals we call essential oils.
Rosemary oleoresin is made by infusion -- by soaking the same plant material in a solvent. The solvent dissolves the essential oils and other less-volatile chemicals in the plant material. The solvent is removed, leaving the "oleoresin extract" behind. An oleoresin extract contains essential oil as well as the heavier resins, waxes, and oils also dissolved by the solvent.
What kind of ROE to use?
ROE is usually sold in varying strengths as measured by its carnosic acid content which can range from 2% to 7%.
I recommend purchasing ROE with 5% to 7% carnosic acid for use in bulk fats and in soap and other bath-and-body products.
If you plan to use ROE in other products, you may want to purchase a less concentrated product for ease of weighing and measuring.
Another option is to purchase a higher-strength ROE and dilute a portion with a mild oil, such as sunflower oil. Use this diluted ROE when you only need a tiny amount of ROE.
A few US suppliers of ROE are Lotioncrafter (7% strength), Wholesale Supplies Plus (7%), Majestic Mountain Sage (2% and 5%).
What if I can only find Rosemary Seed Extract, not ROE?
An alternate common name for Rosemary Oleoresin is Rosemary Seed Extract. Since ROE is an extract of the leaves and stems, this alternate name is confusing.
The key is to look at the INCI (official) name -- Rosemarinus officinalis (Rosemary) Leaf Extract (and) Helianthus annus (Sunflower) Seed Oil.
Note: The oil and the extract may be in reverse order or the oil may be omitted, depending on the supplier.
How much should I use?
I suggest no more than 0.5 grams ROE per 1000 grams of fat (0.05% based on total fat weight) to help preserve fats in storage or for use in soap.
ROE weight = Fat weight X 0.05 / 100 = Fat weight X 0.0005
The dosage range I have found reported in the literature is 0.2 to 1.0 g ROE per 1000 g fat (0.02% to 0.1% based on total fat weight). If you want to use another dosage other than 0.05%, replace the 0.05 in the formula above with the number you want to use instead.
These numbers are based on ROE with 5% to 7% carnosic acid content. If the carnosic acid content in your ROE is lower than that, then adjust the dosage accordingly.
Kevin Dunn recommends 1.0 g ROE for every 1000 g oils (0.1% of total fat weight) to be added when making soap. He found ROE by itself to be an effective "natural" treatment for rancidity (DOS, dreaded orange spots) in soap. He suggests an even more effective but less "natural" combination of 1.0 g ROE and 0.5 g tetrasodium EDTA powder for every 1000 g oils. (3)
Do not use more ROE than necessary!
Too much antioxidant can accelerate the oxidation of fats, a process called "pro-oxidation."
Stick with the recommended dosage -- more ROE is not better! Also do not double dose -- if you add ROE to your stored fats, do not add more ROE when making soap.
One study looked at the antioxidant and pro-oxidant effects of ROE in soybean oil. The researchers found ROE was ineffective at 0.01% and it was pro-oxidant at 0.5%. They found ROE worked best as an antioxidant in the 0.02% to 0.05% range. (4)
How should I use it?
Stored fats: Add ROE to liquid fats after you buy them to protect against oxidation and rancidity during storage. ROE is especially helpful for protecting oils high in polyunsaturated fatty acids, such as grapeseed and hemp, but it is beneficial for all liquid fats, as well as for home-rendered lard and tallow.
Other fats naturally have long shelf lives or have been hydrogenated and treated with antioxidants and chelators to lengthen their shelf lives. Adding ROE to these fats for storage is not required. These fats include coconut, palm kernel, and palm, as well as commercially produced lard and tallow.
Since ROE is a thick syrup, it will not mix easily into liquid fat if you just put ROE directly into a large container of liquid fat. A better way is to pour out a little fat (100-200 mL or 1/4-1/2 cup) into a cup, mix the ROE into that fat until you can't see any trace of the ROE syrup, add this mixture to the large container of oil, and shake or stir well.
If you home-render lard or tallow, stir ROE into the warm liquid fat right after rendering.
Soap: Stir ROE into the fats before adding your lye solution.
When making soap with fats treated with ROE, you may notice the soap batter briefly turns bright orange right after the lye solution is mixed into the fats. In my experience, this blush of color fades away after several minutes, and the finished soap is not discolored.
How much lye does it neutralize?
None! Do not adjust your lye weight for ROE.
(1) O. I. Aruoma, B. Halliwell, R. Aeschbach & J. Löligers. (1992) Antioxidant and pro-oxidant properties of active rosemary constituents: carnosol and carnosic acid. Xenobiotica, 22:2, 257-268, DOI: 10.3109/00498259209046624. https://www.tandfonline.com/doi/abs/10.3109/00498259209046624
(2) R Tisserand, R., Young, R. Rosemary. Essential Oil Safety, 2nd ed. Churchill, Livingstone, Elsevier. 2014. pg 407-409.
(3) Dunn, K. Scientific Soapmaking. Clavicula Press. 2010. pg 279-286.
(4) Hall, C., Cuppett, S. The effects of bleached and unbleached rosemary oleoresins on light-sensitized oxidation of soybean oil. J Am Oil Chem Soc 70, 477–482 (1993). https://doi.org/10.1007/BF02542579
(5) Nieto, G., Ros, G., & Castillo, J. (2018). Antioxidant and Antimicrobial Properties of Rosemary (Rosmarinus officinalis, L.): A Review. Medicines (Basel, Switzerland), 5(3), 98. https://doi.org/10.3390/medicines5030098
(6) Turan, S. Effects of some plant extracts on the oxidative stability of canola oil and its purified triacylglycerols. Journal of Food Quality 37 (2014) 247–25. https://onlinelibrary.wiley.com/doi/pdf/10.1111/jfq.12086
(7) Damechki, M., Sotiropoulou, S., & Tsimidou, M. (2001). Antioxidant and pro-oxidant factors in oregano and rosemary gourmet olive oils. Grasas y Aceites, 52(3-4), 207-213. DOI:http://dx.doi.org/10.3989/gya.2001.v52.i3-4.359. http://grasasyaceites.revistas.csic.es/index.php/grasasyaceites/article/view/359
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