Levan in Cosmetics: Summary
FRUCTANS: One of the most attractive properties of levan is the safety of this polysaccharide for both the user and the environment. It is a polymer of fructose produced by low impact fermentation using an organism which has not been genetically modified. Levan is not cytotoxic and includes no animal derivatives. Levan contains no allergens as listed in the 7th Amendment to the European Cosmetics Directive. Testing on our preparation showed no skin or eye irritation. Further there was no indication of allergic contact sensitization.
A second selling point for levan is that it has several properties which distinguish it from other polysaccharides. Levan forms 50-200 nm diameter spheres which give the material a smooth feel. A thin coating of levan dries to a hard, shiny finish.
Unlike polysaccharides used as emulsifiers and thickeners, levan does not swell in water and has an unusually low intrinsic viscosity at 0.14 dl/gm. Levan-based films are good oxygen barriers. For a bio-based material, levan is relatively acid stable. Dissolved in 1 N HCl and held at 70 °C, levan is only partially hydrolyzed after 1 hour. Levan absorbs UV radiation, particularly in the UV-C range.
- Film Former
- Water Soluble
- Low Intrinsic Viscosity
- High Molecular Weight
- Produced by Non-GMO
- No Skin or Ocular Irritation
- 50-200 nm Diameter Spheres
- No Allergic Contact Sensitization
PRODUCTION: The Montana Polysaccharides levan is produced by a species of Bacillus in a tightly controlled fermentation of sugar. The organism is NOT genetically modified. Production is at Cathay Biotechnology (www.cathaybiotech.com) and is sold under the trade name Levana™.
NO OCULAR IRRITANCY: Ocular irritancy tests have shown levan is safe for use near the eye.
Chorioallantoic Membrane Vascular Assay (CAMVA 14 day)
- RC50 >3.0% = Non-irritant
- RC50 >1.0% <3.0% = Indeterminate
- RC50 <1.0% = Irritant
Interpretation: CAMVA tests are conducted on egg chorioallantoic membranes. A higher number denotes less irritation. At 87% (well above the 3% threshold for a non-irritant), the CAMVA test indicates levan is not causing irritation.
Bovine Corneal Opacity and Permeability Test (BCOP)
- 0-25 = Mild irritant
- 25.1 - 55 = Moderate irritant
- 55.1 and above = Severe irritant
Interpretation: For this test, a lower number points to less irritation. The BCOP score of minus 0.94, indicates marginally less irritation for corneas treated with levan than the saline controls.
NO DERMAL IRRITATION OR ALLERGIC CONTACT SENSITIZATION: Skin tests were completed on 52 subjects. For the induction phase, levan patches were applied three times per week for a total of nine applications. Patches were removed after 24 hours and the site evaluated. Two weeks after the induction phase had been completed, challenge patches were applied and scored at 24 and 72 hours. The zero scores in both series indicated no dermal irritation or allergic contact sensitization.
NO CYTOTOXICITY: Levan is not cytotoxic in the Agar Diffusion Test.
SOLUBILITY: Levan is considered to be water "soluble." Technically, perhaps it would be more accurate to refer to levan in water as a suspension that does not readily settle out. Large flakes require several hours to dissolve in cold water. Powdered levan will solubilize more rapidly as will solutions made with hot water. A thin film of levan will dissolve quickly in warm water.
Levan may be made water insoluble by tying up a portion of the available hydroxyl groups. The most successful approach found to date has involved cross-linking. The method uses an emulsifiable diphenylmethane diisocyanate (MDI) sold by Huntsman. Alternatively, a food grade product from Bayer, hexamethylene diisocyanate (HDI) sold as Bayhydur 302 has been used but has a very short open time. Another approach is to derivatize levan for increased water resistance.
Levan does not dissolve in most organic solvents and is unaffected by alcohols, d-limonene and methylethylketone. The only organic solvent found useful to date is DMSO.
VISCOSITY: Levan has an unusually low intrinsic viscosity at 0.14 dl/gm. In comparison, dextrose has an intrinsic viscosity around 1 dl/gm and materials used as thickeners typically have intrinsic viscosities in excess of 100 dl/gm.
DOES NOT ENCOURAGE MICROBIAL GROWTH: Unlike some natural products, levan does not encourage growth of fungi and bacteria. Cultures of Aspergillus sp., Cladosporium sp., Brevibacillus sp., Staphylococcus epidermidis, and Micrococcus sp. were grown on levan coated agar plates and on treated construction materials. Organism growth was not visibly different from that of untreated controls. Although levan did not enhance microbial growth, neither did it hinder the growth of existing bacteria and fungi.
ADHESIVE PROPERTIES: Levan has good adhesive strength. The following table shows the tensile strength of levan compared with other natural polymers when used to bond bare aluminum coupons. It should be noted that these tests used levan dissolved in water with no additives. It may be anticipated that formulated glues based on levan would have a superior performance.
Tensile strength is average of 9 or 10 replicates using bare aluminum coupons.
FILMS: Levan is a film former. With no additives, levan films are brittle. Adding clay such as 10-50% montmorillonite or 2% Laponite® produces a film that is flexible, translucent, not sticky and water resistant. Glycerol may be included at a rate of 0.2-5% to increase film flexibility. Other suitable plasticizers are PEG and sorbitol. Plasticizers tend to negate the water resistance effect of clay.
RAW MATERIAL: Levan is sold under the trade name Levana™ as flakes or a powder. It has an extended shelf life as long as it remains dry. To obtain the desired concentration, levan is simply dissolved in water. Levan can be applied as a fine spray, drying to a hard coating. Adhesive applications generally require 20-30% solutions while cosmetic applications typically incorporate 1-10% levan. This levan is a raw material; no attempt has been made to formulate a finished product. Levan is both the INCI and scientific name. The CAS number for levan is 9013-95-0.