Acidified Foods: Definitions and Regulations

by: Martha Kimber, M.S.

Definition of Acidified Foods

Per 21 CFR 114, acidified foods are “low-acid foods to which acid(s) or acid food(s) are added... with a water activity greater than 0.85 and a finished equilibrium pH of 4.6 or below.” These foods are shelf-stable.

Examples of Acidified Foods

Included Products

• Products that contain large pieces of low acid components (cucumber, beets, onions, peppers, onions, some fruits, etc.)
• Dressings, salsas, and condiments with large amounts of low acid ingredients (sugar, milk powder, dried spices, starch, anchovy, etc.).

Excluded Products

• Alcoholic beverages
• Carbonated beverages
• Fermented foods
• Naturally acidic foods
• Syrups and pastes with a water activity <0.85
• Refrigerated and frozen products

Applicable Regulations

Acidified foods are governed by several federal regulations:

• 21 CFR 114: defines acidified foods and outlines processing and record-keeping requirements
• 21 CFR 108: covers requirements, exemptions, and considerations for permits when packaging and selling acidified foods
• 21 CFR 117: applicable to all FDA-regulated foods, details cGMP, hazard analysis, and preventive controls under the Food Safety Modernization Act (FSMA)
• In some states, there are additional requirements (e.g. the Cannery Inspection Program in California)

Regulations mandate that acidified foods be thermally processed and hot-filled into the final packaging, with some exceptions. If the acidified food is not thermally processed or is cold-filled into its final packaging, scientific data must be collected by conducting a laboratory challenge study to demonstrate that microbial pathogens of public health concern naturally die-off in the product and spoilage microorganisms of non-health significance do not reproduce in the product. The product pH, acidulant, and any preservatives that are added to the product may be used as effective microbiological controls in lieu of thermal processing and hot-filling processes.

Classification of Acidified Foods vs. Acid Foods

The key safety concern for acidified foods is based on the potential for Clostridium botulinum growth. The preamble to the rule is focused on products that contain a large percentage of non-acid ingredients, large particles of non-acid ingredients, or take a long time to reach a pH equilibrium below pH 4.6.

Products that do not contain particulates, contain only a small amount of low-acid ingredients, and/or reach equilibrium pH rapidly should not be considered acidified foods but may be considered “formulated acid foods” and may therefore be excluded from acidified food regulations.

An experienced processing authority (PA) should be consulted to determine whether a product may be considered to be an acidified or a formulated acid food. If the product is classified as a formulated acid food, a process authority letter should scientifically justify the exclusion.

If the product is classified as an acidified food and the food is cold filled (not aseptically) and it's not thermally processed, it is important that you work with your PA to design and execute an appropriate challenge study that is specific to your product formulation and desired process.

“What is considered a “small amount” of low acid ingredients in a food? I've heard that the cut-off is less than 10% of formulation.”

While 10% of the total formulation is often used as a general guide to initiate an evaluation, it is not accepted by FDA as a formal criterion. There is no defined value for “small amount” by the FDA. Furthermore, the percentage of low acid ingredients in a formulation is just one factor among several that should be considered by your PA. It is also important to consider the process required in achieving the product’s target equilibrium pH and how much of a pH shift occurs during acidification steps.

Microbiological Safety Considerations

Historically, acidified foods have a great food safety record. Largely this can be attributed to the extensive regulations in the US. There are very few instances where acidified products have been implicated in foodborne illness outbreaks. The few cases that have occurred were not commercially produced products but home canned products that were improperly acidified.

Organisms of Concern

In general, many foodborne pathogens of public health concern require favorable conditions in order to grow and/or produce toxin in a food product. Clostridium botulinum, Clostridium perfringens, Staphylococcus aureus, and Bacillus cereus all require favorable conditions to either germinate and produce toxin or grow to high population levels before producing toxin. These pathogens are often controlled by pH. For example, Clostridium botulinum is inhibited by a pH level of 4.6 and is therefore not considered to be a pertinent organism of concern for properly acidified foods.

Other organisms, such as Escherichia coli O157:H7, Salmonella species, and Listeria monocytogenes are so pathogenic, even at very low population levels, that their mere presence in a food may result in foodborne illness and favorable growth conditions for replication are not required. These pathogens may survive for long periods of time in a food product, even if the environment is unfavorable or acidic enough to inhibit growth. Therefore, the presence of E. coli O157:H7, Salmonella species, and L. monocytogenes in acidified food products presents a public health risk. These three pathogens are often selected as primary organisms of concern for acidified food products.

Common spoilage organisms of concern for acidified foods typically include yeasts, molds, lactic acid bacteria, and acid-tolerant bacilli. The growth of these groups of organisms in a food product does not represent a food safety risk but can result in product spoilage and economic loss. All four groups of these organisms are tolerant of low pH levels but minimum tolerances vary by species. Some of these spoilage organisms are also known for their heat-resistance and ability to survive standard pasteurization treatments applied to acidified foods, such as heat-resistant molds (HRM) and Alicyclobacillus spp. (ACB). In most cases, HRMs and ACBs cannot be controlled by thermal processing but can be excluded from products through the use of high quality ingredients, preservatives, and strict adherence to GMPs and sanitation protocols.

Thermal Processing of Acidified Foods

Thermal processing is the standard processing requirement for producing acidified foods, using heat for a defined period of time to address microorganisms. The two primary goals for thermal processing are:

1. Inactivate vegetative pathogens capable of surviving and causing illness. Even if they are present at very low levels, these have a low infective dose, and may still cause foodborne illness upon consumption.
2. Ensure that the product is shelf stable by inactivating spoilage organisms that can reproduce in the product under normal conditions of storage, distribution, and retail.

Is thermal processing of acidified foods required?

A thermal process is not always necessary to ensure microbiological safety. In some cases, a formulation control approach may be used, which utilizes the product’s intrinsic parameters (pH, titratable acidity, preservatives, etc.) in order to achieve microbial lethality against pertinent vegetative pathogens.

The efficacy of the formulation itself to deliver pathogen lethality must be scientifically validated and is defined as the amount of time required to achieve a 5-log reduction of pertinent pathogenic organisms. When filing, the FDA cold-fill-and-hold process form 2541e should be submitted, along with a copy of the scientifically designed challenge study specific to your product.

“Cold” or Ambient-Filled Acidified Foods

The FDA terminology “cold fill”, implies that the product is a refrigerated food, but in reality this term indicates that a product is filled into its final packaging under ambient conditions (not hot-filled). There are several types of cold-fill procedures:

1. The product is thermally processed, cooled, and then aseptically filled into the final packaging.
2. The product is thermally processed, cooled, and ambient-filled into the final packaging (not aseptic).
3. The ingredients are batched without a thermal process and then ambient-filled into the final packaging.

Processes 2 and 3 are commonly used for dressings, sauces, and preserved beverages, which are commonly packaged in lightweight plastic bottles such as PET which cannot withstand typical hot-fill temperatures.

Challenge Studies for Cold-Filled Acidified Foods

Challenge studies may be used to validate the safety of cold-filled acidified foods. Many industry and scientific resources are available for reference and provide guidance on proper study design (Breidt et al., 2018; NACMCF, 2010). Key design considerations include:

1. Product selection. Test multiple product lots or a representative “worst case scenario” formulation. Formulation attributes (including pH, salt, preservatives, titratable acidity, type of acidulant, etc.) should be considered when selecting representative product samples for the study.
2. Pathogen strain selection. Use multi-strain inoculum cocktails of pertinent pathogenic organisms, including Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica. When possible, strains that were recovered from similar high acid products, outbreaks, and clinical isolates should be selected. Each pathogen inoculum cocktail should be tested separately.
3. Acid adaptation. The cultures should be acid-adapted prior to inoculation to mimic real product conditions.
4. Inoculum level. Sufficiently high inoculum levels should be used so that 5-log reductions can be demonstrated.
5. Incubation temperature and time. Selected storage temperature should be based on the lowest expected condition during warehousing. Warehouse conditions for most shelf stable, acidified food products are not controlled, and in colder climates 10°C/ 50°F typically considered to be “worst-case scenario”. The incubation time should align with what can be reasonably expected during warehousing before product release.
6. Test replicates. Include at least three replicates per product formulation, target pathogen, and sampling time.

The results of the challenge study should provide the minimum storage temperature and minimum storage time required to achieve 5-log reductions of pertinent vegetative pathogens for a given product formulation. The challenge study report can be used as a supporting document for your FDA filing.

FDA Filing Procedure for Acidified Foods

Filing acidified foods with the FDA involves the following:

1. Form 2541: Register the processing facility as a Food Canning Establishment (FCE).
2. Form 2451e: Submit process filing details for the acidified food.
3. Process authority letter: Include with your filing, this document details the critical factors for the thermal process, if applicable, such as process time, temperature, flow rate, etc., as well as the product formulation critical factors.
4. Challenge study final report: Required for cold-filled products, which clearly states the product intrinsic parameters (pH, preservative level, etc.) as well as the extrinsic parameters (storage time, temperature) required to achieve safety.
5. State requirements: Some states, such as California, act as a process authority and have additional requirements that must be followed in addition to the federal requirements.

Do you have questions about how to apply this knowledge to your product or process?

Connect with an expert.

References

Breidt Jr, F., Andress, E. L., & Ingham, B. (2018). Recommendations for Designing and Conducting Cold-fill Hold Challenge Studies for Acidified Food Products. Food Protection Trends, 38(5).

National Advisory Committee on Microbiological Criteria for Foods. (2010). Parameters for determining inoculated pack/challenge study protocols. Journal of Food Protection, 73(1), 140-203.

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