METHYL P-HYDROXYBENZOATE

CAS: 99-76-3 ANTIMICROBIAL AGENT, FLAVORING AGENT OR ADJUVANT

Methyl p-hydroxybenzoate, commonly known as methylparaben, is a synthetic preservative used primarily for its antimicrobial properties and, in some regulatory frameworks, as a flavoring adjunct as permitted under defined conditions.

What It Is

Methyl p-hydroxybenzoate is a chemical compound identified by the CAS Number 99-76-3 and widely known in regulatory and food science contexts as methylparaben. It belongs to the class of organic esters derived from p-hydroxybenzoic acid. Other synonyms include the names listed in the "other_names" field above. In food technology, this compound is categorized by its technical functionality as an antimicrobial agent and, in some jurisdictions, also as a flavoring agent or adjuvant. Its molecular structure features a methyl ester bound to the para position of a hydroxybenzoic acid core, giving it properties that can inhibit microbial growth in formulations where microbial stability is a priority. The compound appears in solid form as colorless crystals or a white crystalline powder with little to no distinct odor. It displays solubility characteristics that allow it to dissolve readily in organic solvents, including alcohols and ethers, but its solubility in water is limited. These physicochemical attributes inform how it is handled during ingredient formulation and how it is specified in regulatory monographs or food additive specifications. Methyl p-hydroxybenzoate has been recognized in international additive systems, where it is commonly referred to as INS 218 or E218. This designation follows the International Numbering System (INS) for food additives, which is coordinated under the Codex Alimentarius framework and provides a shorthand for identifying approved additives across jurisdictions. Its inclusion in these systems reflects historical evaluations of its technological efficacy and safety profile in food science.

How It Is Made

The synthesis of methyl p-hydroxybenzoate is a classical esterification process involving the reaction of p-hydroxybenzoic acid with methanol. In this reaction, p-hydroxybenzoic acid is brought into contact with excess methanol in the presence of an acid catalyst, such as concentrated sulfuric acid, which facilitates the removal of water formed during ester bond formation. After esterification, the reaction mixture typically undergoes purification steps that can include distillation to remove residual reactants and catalysts, followed by crystallization or filtration to isolate the methyl p-hydroxybenzoate product in a high-purity form. The specification for the purity of the final product is guided by food additive monographs and compendia, such as those developed by the United States Pharmacopeia and other regional food chemical codices. These standards ensure that the resulting compound meets identity and purity requirements suitable for its intended use in food and related applications. The esterification process and purification are designed to yield a substance that is free of significant contaminants that might compromise its safety or technological function. In manufacturing practice, ensuring consistent quality and adherence to specification is critical, especially when the compound is destined for regulated food use. Good manufacturing practices (GMP) and quality control testing, such as assay for active compound content and limits on impurities, are implemented to meet regulatory thresholds and to maintain confidence in the ingredient's performance and safety within food systems.

Why It Is Used In Food

Methyl p-hydroxybenzoate is used in food applications primarily for its antimicrobial properties. Its capacity to inhibit or slow the growth of spoilage microorganisms such as yeasts and molds helps to extend the shelf life of perishable food products. This attribute can be particularly valuable in products with moderate water activity or in acidic environments where microbial proliferation is a concern. The compound’s efficacy against specific spoilage organisms contributes to maintaining product quality over defined storage periods. In addition to microbial control, methyl p-hydroxybenzoate may also be used in some regulatory frameworks as a flavoring agent or adjuvant, although such use is tightly controlled and subject to jurisdictional guidelines. Its role as a flavoring adjunct tends to be secondary to its preservative function, where its presence can support the stability of flavor compounds and overall sensory quality over the product’s shelf life. Food formulators often select methyl p-hydroxybenzoate in combination with other preservatives or food additives to achieve a broader spectrum of effectiveness or to tailor preservation strategies to the specific intrinsic and extrinsic properties of a food product. Its compatibility with a range of food matrices means it can be applied in diverse product categories, always guided by the regulatory requirements that define acceptable levels and application conditions for each category.

Adi Example Calculation

To illustrate how an acceptable daily intake (ADI) might be interpreted in a hypothetical scenario, consider a person weighing 70 kilograms. Using an ADI value expressed as an upper bound of a group range, such as 10 mg per kilogram body weight per day, the calculation estimating a lifetime daily intake that would be considered acceptable under regulatory assessment would proceed as follows: If the ADI is 10 mg per kilogram body weight per day, a 70 kg person would have an ADI threshold of 70 x 10 mg = 700 mg per day. This represents the amount that, based on regulatory risk assessment, could be consumed daily over a lifetime without posing a safety concern under the assumptions and data used to establish the ADI. It does not mean that an individual should seek to consume this amount, nor does it imply that typical consumption approaches this level. Actual dietary intake of the compound through foods containing it at regulated use levels is expected to be substantially lower. This example is purely illustrative and is not a recommendation for individual dietary intake.

Safety And Health Research

Regulatory bodies evaluate the safety of additives such as methyl p-hydroxybenzoate based on a comprehensive review of toxicological data, exposure assessments, and mechanistic studies. The Joint FAO/WHO Expert Committee on Food Additives has provided evaluations that inform the acceptable daily intake and group assessments for related compounds. These evaluations consider endpoints such as general toxicity, effects on organ systems, and, where data are available, reproductive and developmental toxicity. Source: JECFA chemical database. A key aspect of safety assessment is the consideration of how the compound behaves in the body. Methyl p-hydroxybenzoate is absorbed and metabolized, with hydrolysis to p-hydroxybenzoic acid and subsequent excretion, a metabolic pathway that underpins many risk assessments. Regulators also consider available evidence regarding potential endocrine activity or other mechanistic effects, balancing these with observed outcomes in animal studies. Historical evaluations by scientific panels have explored these mechanistic aspects, particularly within the context of parabens as a class, noting differences among members of the class in potency and biological activity. Source: EFSA AFC Panel opinion. Toxicological data, such as studies assessing high-dose exposures in laboratory animals, contribute to establishing points of departure for risk assessment and, in turn, inform acceptable daily intake derivations. The rigorous review of these data and application of safety factors aim to ensure that permitted uses of the compound in food systems maintain a margin of safety for consumers.

Regulatory Status Worldwide

Methyl p-hydroxybenzoate’s regulatory status varies by jurisdiction and application context. In the United States, the compound is recognized in the Code of Federal Regulations as methylparaben under 21 CFR 184.1490, where it is listed among substances that are permitted for use in food under the conditions specified in that regulation. This regulatory entry defines its identity and permitted use as an antimicrobial agent within food formulations when employed in accordance with good manufacturing practice. The inclusion of methylparaben in this section of the CFR signals that the U.S. Food and Drug Administration (FDA) considers it acceptable for defined food uses under prescribed conditions, although precise usage levels are guided by product category regulations and GMP. Source: eCFR 21 CFR 184.1490. Internationally, the compound is addressed by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), which evaluated methyl p-hydroxybenzoate along with structurally related esters and established an acceptable daily intake (ADI) range as part of a group evaluation. The JECFA evaluation supports a group ADI of 0-10 mg/kg body weight for methyl and ethyl parabens, indicating a level of dietary intake considered acceptable across a lifetime without appreciable risk, based on available toxicological data. Source: JECFA chemical database and FAO monograph. In Europe, historical opinions by the European Food Safety Authority (EFSA) Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food have reviewed parabens as a class of food additives. These evaluations have addressed safety considerations and group ADI settings for methyl and ethyl parabens, while noting data limitations for other parabens. Source: EFSA AFC Panel opinion on paraben usage in food. However, the current status of methyl p-hydroxybenzoate as a permitted food additive under EU food additive legislation may differ and requires reference to updated Union lists and regulations specific to food additive authorization.

Taste And Functional Properties

In sensory terms, methyl p-hydroxybenzoate contributes little to taste or aroma when used at concentrations typical of antimicrobial preservation. It is generally described as having a neutral to slightly bitter sensory profile at higher concentrations, but at the low concentrations permissible for food use, any sensory contribution is negligible. As with many preservatives, the functional properties of methyl p-hydroxybenzoate are rooted not in flavor enhancement but in its ability to support product quality by mitigating microbial degradation. Functionally, the compound exhibits stability across a range of pH conditions compatible with acidic and moderately acidic food systems. Its solubility profile means it may require formulation strategies, such as dissolution in alcohol-based carriers or incorporation into premixes, to achieve uniform distribution in aqueous matrices. Thermal stability is sufficient to withstand various processing conditions typical of food production, although as with any ingredient, compatibility with specific processing parameters should be verified in formulation trials. Methyl p-hydroxybenzoate’s functional performance is influenced by factors such as product composition, water activity, and storage conditions. In conjunction with other preservative systems, it can contribute to a multi-hurdle approach to food preservation, where combined barriers limit microbial growth and support product safety and quality.

Acceptable Daily Intake Explained

The concept of acceptable daily intake (ADI) is a risk assessment tool used by international regulators to describe the amount of a substance that can be consumed every day over a lifetime without appreciable health risk. It is typically expressed in milligrams of the compound per kilogram of body weight per day. For methyl p-hydroxybenzoate and related compounds, a group ADI reflects consideration of cumulative exposure to these structurally similar substances. The group ADI established by JECFA for methyl and ethyl parabens is expressed as a range, indicating a boundary of intake that regulatory toxicologists consider safe based on available data. This range is derived from detailed analysis of animal studies and the application of safety factors that account for uncertainties in extrapolating animal data to humans and variability within human populations. Regulatory bodies use the ADI as a guide in establishing permissible uses and concentrations of additives in food products. It is important to clarify that an ADI is not a recommended level of intake for individuals, nor is it a target to achieve; rather, it is a conservative benchmark used in regulatory evaluation to help ensure consumer safety. The actual intake of an additive by a consumer depends on the frequency of consumption of products containing that additive and the levels at which it is used in those products.

Comparison With Similar Additives

Methyl p-hydroxybenzoate can be compared with other parabens such as ethyl p-hydroxybenzoate and propyl p-hydroxybenzoate based on structural and functional characteristics. All parabens are esters of p-hydroxybenzoic acid and share a common mechanism of antimicrobial activity, but their relative efficacy and regulatory considerations can differ. For example, ethylparaben, which has a slightly longer alkyl chain, often demonstrates a similar spectrum of antimicrobial activity but may exhibit different solubility and sensory properties. Regulatory evaluations have historically grouped methyl and ethyl parabens together when setting acceptable daily intake ranges, indicating similar safety profiles for these two compounds under certain reviewed conditions. Source: JECFA and EFSA opinions. Propyl p-hydroxybenzoate, with an even longer alkyl chain, has been subject to specific evaluation due to differences in toxicological outcomes in animal studies. Regulators have sometimes excluded propylparaben from group ADIs for methyl and ethyl parabens when data suggest differential effects at certain endpoints, underscoring the need to consider individual compounds within a class. Source: WHO JECFA database. Comparing methyl p-hydroxybenzoate with non-paraben preservatives, such as sorbic acid or benzoic acid derivatives, highlights differences in spectrum of activity, solubility, and regulatory limits, which influence how food scientists select preservatives based on product attributes and regulatory frameworks.

Common Food Applications Narrative

Methyl p-hydroxybenzoate finds application in a variety of food formulations where microbial stability is essential. In beverages with extended shelf life, including syrups and acidic drinks, it can be employed as part of a preservative system to slow spoilage by yeasts and molds. Its utility extends to confectionery products that are susceptible to fungal growth when moisture content and storage conditions favor spoilage. In fruit preparations and sauces, where pH and water activity create environments conducive to microbial proliferation, methyl p-hydroxybenzoate may be used in combination with other additives to support stability over distribution and retail storage. It also can be found in baked goods with extended shelf requirements and in products with intermediate moisture content where traditional preservative strategies are needed to maintain quality. Because different jurisdictions have unique regulatory allowances, the specific food categories in which it appears vary. However, its core technological function remains consistent: preserving product quality by mitigating microbial growth. Where permitted by local regulatory authorities, manufacturers rely on this compound to help meet shelf life targets without compromising organoleptic properties. Whether in syrups, preserved fruit components, or similar products, methyl p-hydroxybenzoate serves as a tool in the food technologist’s preservation toolkit.

Safety & Regulations

FDA

  • Approved: True
  • Regulation: 21 CFR 184.1490

EFSA

  • Notes: EFSA has provided safety opinions on parabens but current EU authorization and ADI specific to food additive use require reference to contemporary EU lists.
  • E Number: E218

JECFA

  • Year: 1973
  • Ins Number: 218
  • Adi Display: 0-10 mg/kg bw
  • Adi Mg Per Kg: 10

Sources

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