Introduction
Preservation ingredients represent a significant shift in the beauty & personal care industry, driven by consumer perception of ingredient safety. Consumers are more informed and opinionated about the ingredients in their products and have championed changes such as the paraben-free movement, the clean beauty movement, and a multitude of other waves of "free-from" claims.
While this poses a challenging opportunity for scientists, what consumers want is simple:
- Products that are safe for their bodies
- Products that provide efficacy without excess
- Products made from simple, natural and sustainable ingredients
Preservation is a particularly important topic because effective preservation is not optional. Preservative systems are required to maintain safety of a formulation by keeping it free of microbial contamination. At Inolex we have embraced the challenge of a changing preservation landscape with safe and effective alternative preservation options. Our technology options center around the Hurdle Technology approach to preservation.
What is Hurdle Technology?
Hurdle Technology was first popularized as a preservation approach in the food industry. It is an intelligent combination of different preservation factors or techniques ("hurdles") to achieve broad spectrum, mild and reliable preservation effects. In beauty & personal care formulations, we combine multiple techniques to create an environment that is inhospitable to microbial growth. The multiple techniques include various benefits from ingredients, as well as processing procedures:
- Common ingredient functions that create hurdles include membrane disruption and iron chelation.
- Formulation hurdles include low pH and employment of Good Manufacturing Practice (GMP) principles.
Membrane Disruptors: Medium Chain Terminal Diols
Medium Chain Terminal Diols (MCTDs) are an important class of multifunctional ingredients that are known to control microbial growth in cosmetic formulations. Caprylyl Glycol (Lexgard® O) and Ethylhexylglycerin (Lexgard® E) are commonly used MCTDs. More recently, 100% plant-based options have emerged such as Glyceryl Caprylate (Lexgard® GMCY MB) and Methylheptylglycerin (Lexgard® MHG Natural MB).
MCTDs are effective preservation components because they are membrane disrupters. The MCTDs interact with the cell membrane lipids leading to disruption of the cell membrane. This allows other ingredients to enter the cells and water to leak out of the cells, leading to eventual cell collapse. Common MCTDs contain a short alkyl chain (C6 - C10) and terminal hydroxyl groups for optimal membrane disruption. Medium Chain Terminal Diols alone are very effective against bacteria and have low or no efficacy against yeast or mold.
Iron Chelation: Organic Acids
Organic acids are a component of the hurdle technology approach which have been studied since the 1900s. They are often employed in combination with MCTDs to provide increased efficacy against yeast and mold.
Caprylhydroxamic Acid (CHA) is a biostatic organic acid that can be a crucial component of an effective broad spectrum preservation system due to its multiple mechanisms of action. Metal ion chelation, particularly iron chelation, is a critical mechanism for controlling microbial growth, particularly in yeast and mold. Iron is an important nutrient for these microorganisms, and microorganisms that are deprived of iron by chelation cannot proliferate or survive. Most organic acids used as hurdles in preservation systems, including Caprylhydroxamic Acid, also have short alkyl chains (C6 - C10) which provide similar membrane disruption effects as MCTDs.
The Effect of pH on Organic Acid Efficacy
Formulation pH has a significant effect on the efficacy of organic acids as preservation ingredients. To be effective for preservation, organic acids must be in the undissociated (or acid) form. Essentially all organic acids that are effective against microbes are weak acids. This means that when dissolved in aqueous solution, they partially dissociate to their ionized (or salt) form. As the formulation pH is decreased with additional acid, the balance of molecules shifts to an increased concentration of molecules in the undissociated form.
The effect of pH on organic acid preservation efficacy can pose a challenge for formulating products with consumer-friendly preservation ingredients. This is because most organic acids begin to dissociate at pH > 4. The % undissociated acid can be calculated based on the pKa value of that acid. For instance, in a formulation with pH 4, only 50% of the undissociated acid is present for an organic acid with a pKa of 4. In other words, only 50% of the concentration of that ingredient is providing a preservation benefit in the formulation. The concentration of that ingredient that is providing a preservation benefit will continue to decrease as formulation pH is increased.
Caprylhydroxamic Acid is a solution for effective preservation with hurdle technology because it remains undissociated up to pH 8. ~99% of the concentration in formulation, from pH 3 - 8, is present and providing preservation effects. This enables a wide range of formulations that can be preserved with this approach.
Unique Benefits of Caprylhydroxamic Acid
- Effective chelating agent: Metal binding and sequestering is a hurdle mechanism for efficacy against microorganisms. It is the primary mechanism of action for Caprylhydroxamic Acid, which has been shown to be a strong chelating agent for Iron III.
- Similarities to MCTDs: Caprylhydroxamic Acid has a C8 chain and a hydroxamic acid moiety, which is also a polar group. Its chemical structure has many similarities to Medium Chain Terminal Diols, with a similar degree of hydrophobicity. As a result, it is has a comparable ability to disrupt cell membranes.
- Hydroxamic acid: Being a hydroxamic acid, as opposed to a carboxylic acid like most organic acids, CHA has a much higher pKa. This unique attribute means that it is ~99% undissociated in formulation even at pH 7. The amount of “active” CHA is significantly higher than other common organic acids, such as Benzoic Acid.
- CHA + MCTDs: Combining CHA with MCTDs (Spectrastat products) creates a highly effective hurdle technology ingredient combination that can provide broad spectrum microbial growth protection at neutral pH.
- Natural origin: Caprylhydroxamic Acid is 100% natural, with one component derived from coconut oil and the other derived from atmospheric nitrogen and hydrogen.
Caprylhydroxamic Acid and MCTD Combinations
Combination products of CHA and MCTDs allow formulators to easily add just one ingredient to a formulation and have broad spectrum preservation efficacy using the hurdle technology approach.
There are various test criteria against which the preservation efficacy of a system can be measured. The four most popular today are the EP-A criteria, the EP-B criteria, the CTFA (PCPC) criteria, and the ISO11930 criteria. Inolex's CHA-MCTD combinations have been evaluated in a range of formulation types and demonstrated to pass all 4 test criteria. Recommended use levels for each ingredient are based on these preservative efficacy test (PET) data.
In summary, the Safe Preservation portfolio from Inolex offers expansive innovation in the area of preservation alternatives, centered around the application of the hurdle technology approach with novel ingredient combinations.
The proprietary, 100% natural Caprylhydroxamic Acid technology provides formulators with effective preservation options at a wide range of pH levels that are aligned with consumers’ views of ingredient safety.
Combination of CHA with Medium Chain Terminol Diols like Caprylyl Glycol, Glyceryl Caprylate, or Methylheptylglycerin creates complete ingredient systems that enable broad spectrum formulation preservation. These combinations are optimized for use in a variety of formulation types, meeting specific formulation design and production criteria, including 100% natural combinations, high water solubility, cold processability, and a variety of other parameters.
Featured Hurdle Technology Systems
Spectrastat™
Versatile Broad Spectrum Preservation System- Protect against bacteria, yeast, and mold
- Pass industry standard tests at wide pH range
- Alternative to traditional preservatives
- Widely used in the market
Spectrastat™ MHG Natural MB
Multi-Benefit Plant-Based Preservation Innovation- Broad spectrum performance passing industry standard test criteria
- Preserves skin’s microbiome
- Cold processable
- 100% natural & NATRUE approved
Spectrastat™ G2 Natural MB
100% Natural Broad Spectrum Preservation System- Plant-based preservation system
- NATRUE approved & 100% biobased content
- Broad spectrum performance
- Pass industry-standard challenge test
References
- Kabara, J.J. and Orth, D.S., eds., Preservative-Free and Self-Preserving Cosmetics and Drugs., Marcel Dekker, Inc, 1997.
- Leistner, L. (2000). Basic aspects of food preservation by hurdle technology. International Journal of Food Microbiology, 55, 181-186. Doi.10.1016/s0168-1605(00)00161-6.
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