Conventional vs. Natural Preservatives

By Beth Ann Browne u2013 Dow Microbial Control,Phil Geis u2013 AdvancedTesting Laboratories, Tony Rook u2013 The Sherwin-Williams Company | April 30, 2012

Green aspirations must be tempered with practical realities—an environmentally preferable product is not a success if the formulation falls apart or is overrun with potentially pathogenic microorganisms due to the lack of an effective preservative.

The microbiological quality of commercial products is among the most important elements of product quality. Nevertheless, it is an element that has not demanded a hyper-vigilant focus due to the compositions of consumer and industrial products that have prevailed during the past several decades. The use of a conventional chemical preservative along with some innate capacity of the formulation to resist spoilage (due to the high level of solvents and low water content), was previously sufficient to protect the product during manufacturing and throughout its lifetime of use by the consumer. However, modern product formulations with eco-compliant ingredients are under increased pressure by ecolabeling organizations1,2 to abandon the use of conventional preservatives in favor of alternative substances that are seen by various groups to be more “natural.”


Household cleaning products demand effective preservation systems.
Examples of these substances include organic acids, such as citric, lactic, sorbic and benzoic, as well as essential oils and plant extracts, including thyme and rosemary oils.The pursuit of environmental responsibility is to be praised, but there remains a difference between a reactive sustainability strategy that merely reacts to these market trends and a workable practice for the effective preservation of consumer and industrial products. Organic acids and essential oils are not currently suitable direct replacements for conventional preservatives for a variety of reasons including microbial efficacy profiles, product compatibility, regulatory compliance, safety, cost, and supply security. A summary of the points of difference between conventional preservatives, organic acids and essential oils is shown in Table 1 (below).

Consumer and industrial product manufacturers face enormous pressure to offer effective and innovative products at an economical price. Concurrently, consumers and environmental groups are demanding that products be more “environmentally-preferable” in addition to maintaining the same standard of effectiveness at the lowest possible price. With relevant changes such as reduced volatile organic content (VOC), elimination of heavy metals and replacement of solvents with water, products may be perceived as more “green,” but the very real consequence of increased microbial susceptibility must be acknowledged. The removal of ingredients, which once created an inhospitable environment for bacteria and fungi, has a significant impact on product quality. The majority of consumer and industrial products ranging from architectural paint to household cleaners to fabric softeners to dishwashing liquids are now highly susceptible to microbial spoilage. Ineffective preservation of these products and the raw materials used to produce them can have detrimental results including significant changes in viscosity, pH drift, color change and foul odor, all of which can occur while destroying the performance of the product.4

Microbial Efficacy
It is important to specify the positive attributes of conventional preservatives to understand the practical challenges facing natural preservative alternatives. Preservatives are often referred to as biocides, and biocides are by definition toxic and usually lethal to bacteria and fungi. A non-toxic alternative, that is still effective in controlling a broad spectrum of microorganisms, may at best be deemed an unrealistic expectation.

Rosemary oil is not a direct replacement for traditional preservatives.

A successful preservative must be broadly effective against a variety of bacterial and fungal (including molds and yeasts) species, or alternatively a combination of an effective bactericide and an effective fungicide may be used. Consumer and industrial product formulations with a pH range of 2 to12 can be susceptible to both bacteria and fungi. To the extent that organic acids are effective, their effectiveness is limited within a pH range of 2 to 6 and primarily against fungi and a subset of bacteria.
If organic acids were the only preservatives permitted for use in consumer and industrial products, a large gap would exist for products with neutral and alkaline pH, such as laundry detergents and household cleaners, and those subject to the more common spoilage bacteria such as the Pseudomonads.

Factors to Consider
Manufacturing conditions and product compatibility factors must be considered when comparing conventional preservatives to natural alternatives. Some manufacturers require the use of a rapid-acting biocide for the decontamination of products, raw materials, and equipment in order to ensure product quality. If a point is reached when only natural alternatives may be used in consumer and industrial products, the ability to use a rapid-acting biocide will be eliminated.Interestingly, the use of rapid-acting biocides is viewed as environmentally and fiscally responsible by preventing disposal of large volumes of finished products and raw materials that are contaminated with microorganisms. The reduction of bioburden resulting from the use of rapid-acting biocides also reduces the stress on a long-term preservative. It also potentially lowers the amount of long-term preservative required to effectively protect the product from spoilage.

The majority of consumer and industrial products are now highly susceptible to microbial spoilage.
Beyond preserving consumer and industrial products, biocides must be compatible with other ingredients in the formulations. Fortunately, conventional biocides are usually added at less than 0.1% active ingredient, and compatibility issues are infrequent. In contrast, non-traditional (natural alternative) preservatives are typically used at concentrations greater than 1% to achieve antimicrobial efficacy and they may significantly alter other properties of formulations such as viscosity, odor, color, pH and product performance. For example, in a comparison study,5 a household cleaner at pH 10 required 1.0% of an organic acid for effective antibacterial efficacy which reduced the cleaner’s pH to 7.5. This pH shift would alter the product performance to the point of being an ineffective cleaner. A conventional preservative at 0.05% (one twentieth the amount of the organic acid) provided the same level of antibacterial efficacy without altering the pH of the cleaner.5 To achieve potentially the same level of efficacy, organic acids and essential oils are generally required at concentrations of 20 to 50 times and 20 to 200 times greater than the conventional biocides, respectively.5

Sustainable Supply
The global commercial supply for conventional biocides is well established. However, preservatives containing organic acids or essential oils are typically used in small niche product applications due to limited efficacy and therefore are only sold in small volumes (when compared to conventional biocides). A drastic shift to preservatives from agricultural sourcing will not satisfy even a portion of the consumer and industrial markets whose products are made continuously in tens to hundreds of tons per batch. This will require significantly increased percentage levels of natural alternatives for effective preservation.

Even if expanded agricultural production of natural preservatives could be accomplished to satisfy a limited portion of the consumer and industrial product demand, there would be substantial environmental, social and sustainability impacts.6 The authors are currently unaware of existing relevant assessments of these impacts. Additionally, the natural preservative supply would likely be variable,7,8 from crop to crop, and rigorous analysis would be required to determine a consistent active ingredient level from one supply to the next to prevent overdosing or underdosing of a preservative.

Regulatory Compliance
Perhaps the most significant points for this discussion are the regulatory compliance and data reporting requirements for US EPA registration of preservatives for consumer and industrial products. Each preservative used within these products requires EPA registration as an antimicrobial pesticide under the Federal Insecticide, Fungicide, Rodenticide Act (FIFRA) first enacted in 1947 and amended in 1996 (7 U.S.C § 136 et seq.). The EPA states, “All pesticides distributed and sold in the United States must be registered by the EPA based on scientific data showing that they will not cause unreasonable risks to human health, worker, or the environment when used as directed on product labeling.”9 To obtain a registration for a preservative, the preservative supplier must generate an extensive data package including toxicology, environmental fate, exposure, product chemistry and efficacy studies. The EPA evaluates the data and conducts risk assessments. Costs associated with the registration process and data generation can reach $10 million for a new preservative product containing a new active ingredient. A US EPA-approved preservative product label is a company’s license to sell the product, and the label includes specific application areas as well as usage levels.
EPA-registered products are subject to periodic reviews by the Agency, which may result in additional data requirements for the registrant. Suppliers of non-traditional/natural preservative alternatives claiming to control bacteria and/or fungi in a consumer or industrial product that have not obtained a FIFRA registration are in violation of Federal law, unless these natural alternatives qualify as Minimum Risk Pesticides per the criteria for FIFRA 25(b) Exemption.10Product manufacturers that use non-FIFRA-registered ingredients as preservatives within their products, would also be considered non-compliant with Federal law. Currently, only a fraction of FIFRA-registered products contain organic acids or essential oils as the active ingredients.11 All natural products cannot be considered de facto “safe” because some of these materials have been shown to elicit allergic reactions in humans which may be amplified at the high use levels of 1 to 10% required for sufficient antimicrobial performance.12

The Big Picture
The evolution of consumer and industrial product formulations with an increased focus on human and environmental health is a noble effort that is supported by the authors. However, green aspirations must be tempered with practical realities—an environmentally preferable product is not a success if the formulation falls apart or is overrun with potentially pathogenic microorganisms due to the lack of an effective preservative. Current registered preservatives have been thoroughly tested with rigorous regulatory demands not only as to product efficacy but also to ensure adequate protection of human health, proper use and handling, and appropriate consideration of environmental fate. It is not evident that products generally presumed to be more environmentally-preferable would be regarded as such if put to the same scrutiny as a US EPA registered pesticide. The reality today is there are very few effective preservative materials available for formulators to use.

According to some product manufacturers, an eco-label symbol on a product package is required to be competitive in some consumer markets. Conventional biocides are added to final formulations at less than 0.1% (often 0.0015% to 0.05%) active ingredient, yet ecolabel groups judge preservatives by the same criteria as components that are added at significantly higher concentrations, some as high as 60%. These organizations or ecolabels would be restricting certification to product formulations that are compatible with preservation with organic acids or essential oils, or to neutral or alkaline pH products that are inherently resistant to microbial spoilage.

It is clear that efficacy, cost, regulatory compliance and supply have and will constrain application of organic acid and essential oil preservation to niche, if not boutique, products. If market forces or regulatory changes demand the use of only organic acids and essential oils as preservatives, then some categories of products will need to be withdrawn from the market. This would be necessary because the products cannot be made in a way to achieve effective preservation with such materials. Therefore, it is essential that programs intended to establish more environmentally preferable preservation consider products on a case-by-case basis.

In summary, the use of natural alternatives for preservation is not as simple as an ingredient substitution; there are many practical issues to consider in maintaining safe, effective, and stable consumer products that are free from microbial contamination.

1.United States Environmental Protection Agency’s Design for the Environment (DfE), www.epa.gov/dfe.
2. Natural Products Association.Natural Home Care Standard 020910v01.doc www.NPAinfo.org.
3. Generally Regarded as Safe (GRAS) Substances (SCOGS) Database. http://www.fda.gov/Food/FoodIngredientsPackaging/GenerallyRecognizedasSafeGRAS/GRASSubstancesSCOGSDatabase/default.htm
4. American Chemistry Council Biocides Panel. 2010. Benefits of Antimicrobial Pesticides in Public-Health and Industrial Uses.
5. Browne, B.A. 2010. “The Influence of Global Regulatory Requirements and Pressures on Preservative Choices for Consumer Products.”May 6, 2010. Consumer Specialty Products Association Mid-year Meeting.Chicago, IL.
6. United Nations Industrial Development Organization (UNIDO).2005. Herbs, spices and essential oils. Post-harvest operations in developing countries. http://www.unido.org/fileadmin/user_media/Publications/Pub_free/Herbs_spices_and_essential_oils.pdf
7. Barra A. 2009. Factors affecting chemical variability of essential oils: a review of recent developments. Nat Prod Commun. 4:1147-54.
8. Viljoen, A.M., Subramoney, S., van Vuuren, S.F., Baxter, K.H.C. and Demirci, B. 2005. The composition, geographical variation and antimicrobial activity of Lippia javanica (Verbenaceae) leaf essential oils.J Ethnopharm96:271-7.
9. US EPA Registration Review. http://www.epa.gov/oppsrrd1/registration_review/
10. US EPA Reregistration Eligibility Decision (RED) Flower and Vegetable Oils. EPA 738-R-93-031. Dec 1993.
11. US EPA Minimum Risk Pesticides – Criteria for FIFRA 25(b) Exemption.http://www.epa.gov/oppbppd1/biopesticides/regtools/25b_list.htm
12. Bleasel, N., Tate, B., and Rademaker, M. 2002.Allergic contact dermatitis following exposure to essential oils. Australasian Journal of Dermatology 43(3): 211-213.

CSPA Preservative defense Task Force
• The CSPA Microbiology/Preservation Subcommittee is committed to establishing best practices and acceptable standards to address the increasing concern for microbiological quality within consumer and industrial products.To support these goals, a Preservative Defense Task Force was commissioned to address the need of communicating the necessity of effective preservation strategies within consumer and industrial products.

More info: CSPA Microbiology/Preservation Subcommittee,
Tel: 202-872-8110
Website: www.cspa.org

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