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Formulating with Naturals—Skin Care
By: Arthur Georgalas
Posted: February 3, 2011, from the February 2011 issue of Cosmetics & Toiletries.
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The stabilization of these two-phase systems in nature usually involves complex combinations of lipids and proteins. Some commercially available natural emulsions include oleosomes—lipid bodies in oil seeds such as safflower that stabilize vegetable oil droplets for seed storage by coating them in oleosin protein. Mammalian milk is also stabilized by proteins, among which are caseins—one of the major milk protein groups present as micelles that disperse milk fat.7
In addition, plant latex, found in more than 20,000 species including guayule, milkweed, poinsettia and many Euphorbiaceae and other botanical families, is stabilized in laticiferous (milk-forming) systems with the help of proteins plus polar lecithin lipids and other components. Studies8 of the Hevea species, the chief rubber-producing plant, show an adsorbed sheath of protein on the surface, stabilizing the particles of isoprenoid oils that comprise rubber’s source hydrocarbons. This protein gives the oil droplets electrophoretic mobility, i.e. a zeta potential, and stabilizes them via surface electrostatic charges. In fact, many proteins are known to have surfactant properties based on the relative hydrophobicity of their amino acid side chains and ionizable groups, a major factor in governing their tertiary structure. Even relatively small hydrolyzed proteins have surface activity that can contribute to emulsion stabilization. Formulators should look both inside and outside of the cosmetic buyer’s guide for proteins to assist in the natural stabilization of dispersed systems.9
If one allows for simple kitchen chemistry processes such as saponification in the development of natural products, a range of soap surfactants based on vegetable oils are also available, most commonly coconut, palm kernel and soy. Use of the strongly alkaline amino acid arginine in the free base form can be an unusual natural alternative to simple mineral alkali or ammonia for neutralization, replacing the much maligned triethanolamine (TEA).10 In addition, waxes such as beeswax and candellila can supply naturally occurring free fatty acids for soap formation since both have acid values near 20; in fact, one company reports that a certified organic emulsion can be prepared using the US Department of Agriculture’s (USDA) NOP beeswax.11
Other natural amphiphiles that can be combined or used individually include the phospholipid lecithins and lanolin, the wool wax-based mixture of sterol esters, plant sterols and saponins, as well as a range of commercial plant sterol and triterpenoid glycosides extracted from soapwort and agave.
Formulators should note that lecithins can have a varied hydrophilic-lipophilic balance (HLB), depending on the degree of hydrolysis and extraction methods, which can be useful for both o/w and w/o emulsions. Unmodified sterols are exclusively w/o stabilizers whereas the saponin glycosides, as their name implies, act like soaps and are used more for foam generation.