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Formulating with Naturals—Skin Care
By: Arthur Georgalas
Posted: February 3, 2011, from the February 2011 issue of Cosmetics & Toiletries.
page 4 of 5
Natural thickeners and stabilizers from the carbohydrate group of polymers include many of the plant gums of microbial, algal and vascular plant origin. These gums modify the texture and flow properties of emulsions and add to their physical stability. Xanthan gum is a mainstay of food emulsion preparation and is one of the few ingredients named in the USDA’s list of allowed additives to organic-certified processed foods. It imparts the shear thinning rheology with significant yield value necessary to give creams and lotions shelf stability with desired feel at acceptably low use levels of a few tenths percent.
Additional vegetable gums having varying degrees of emulsification, stabilization and viscosity control include tragacanth, scleroglucans, guar, locust bean, carageenan and the alginates, many of which demonstrate synergy, suggesting trials of varying mixtures. Simple insoluble cellulose itself also has been used in the form of citrus fibers and microcrystalline cellulose. Another soluble complex carbohydrate for dispersion enhancement and reduced, more homogeneous emulsion particle sizes is galactoarabinan from the Larch tree. Further, naturals of the mineral variety including swellable clays such as bentonite are useful for their water-structuring ability, forming a hydrated “house of cards” on high shear dispersion. They are also especially effective in combination with natural gums.
The three primary plant metabolite groups described, i.e. lipids, proteins and carbohydrates, provide the scaffold and building blocks for emulsion construction. Some of the starting materials for these polymers also function as humectants in finished products, notably glycerol and amino acids such as pyrrolidone carboxylic acid (PCA) and sugar alcohols such as sorbitol. From the range of secondary plant metabolites identified, mostly polyphenols and terpenoids, the ancillary components of emulsions—colors, fragrances and preservatives as well as some botanical actives, are sourced; botanical actives will be addressed in a future column.
When nature-derived materials are difficult to obtain, nature-identical compounds can be synthesized that function virtually the same—as long as they are not chiral compounds and they are sufficiently purified. The NaTrue organization, for one, goes to great lengths to identify the nature-equivalent preservatives they allow,12 including such organic acids as sorbic, benzoic, salicylic and dehydroacetic and their salts as well as benzyl alcohol.
Allowed organic cosmetic colorants, as listed in the US Code of Federal Regulations (CFR) 21, part 73, include annatto orange-red and beta-carotene, both yellow-orange, oil-soluble carotenoids, as well as carmine, the red polyphenol pigment derived from carminic acid from the cochineal bug. It should be noted that many nature-derived food colorants such as beet extract are only specifically approved for foods, not cosmetics.