Continuing Challenges in Acidified Foods

By Dr. Richard Podolak and Joan Pinkas

In 2010, FDA published the comprehensive “Draft Guidance for Industry: Acidified Foods” to assist food processors in determining what constitutes an acidified food. The document provided nonbinding recommendations to the industry and was not a regulatory mandate. In December 2015, FDA announced the withdrawal of this guidance, in part, because many of the topics addressed in the draft guidance were addressed in other documents.

The withdrawal has prompted many questions from food processors related to pre-acidified ingredients added to the product, the status of water, low-acid powders and low acid liquids, the definition of a small amount of low-acid ingredients, and the definition of a significant shift in pH. The answers to these questions should be based on science, recognizing, for example, that properly pre-acidified ingredients should be judged based on their acidified pH, and that pure water has no buffering capacity and does not influence product pH. Process authorities have the scientific background, technical knowledge, and experience to recommend the parameters and processes that will yield safe food products.

Each food manufacturer is responsible for determining if its products fall into the acidified, acid, or low-acid food categories. If acidified foods are improperly manufactured, they may pose a health hazard to consumers, especially with Clostridium botulinum. As defined in the U.S. Code of Federal Regulations (21 CFR part 114):

• Acid and acidified foods are those that have a pH of 4.6 or lower and a water activity greater than 0.85.
• Acid foods are those that naturally have a pH of 4.6 or lower.
• Acidified foods are foods to which acid or acid food ingredients are added to reach a final equilibrium pH of 4.6 or below. These products must be registered with FDA and produced with the maximum equilibrium pH indicated and according to the requirements in 21 CFR 108.25 and 114.

While these definitions seem straightforward, the devil is in the details. It was, in fact, the finalization of FSMA’s Preventive Controls for Human Foods rule that resulted in the withdrawal of draft guidance for acidified foods, leaving gaps in the interpretation of acidified food policy.

ACIDIFIED FOOD REGULATION. FDA regulations governing the safe manufacture of acidified foods were promulgated in 1979. The main purpose of regulating these products was to prevent botulism due to improper acidification. Clostridium botulinum spore germination, growth, and toxin production will not occur if pH is maintained at or below 4.6.

Until the late 1990s, the safety of acidified foods was viewed as the control of C. botulinum toxin production. But due to the outbreaks of E. coli O157: H7 and Salmonella in apple cider and orange juice, FDA’s Center for Food Safety and Applied Nutrition (CSFAN) proposed in 2001 that all new acidified food-process filings should include a heating or a pasteurization step.

The main purpose of the heat treatment applied to acidified foods is to bring them to a condition of “shelf-stability,” hence to destroy vegetative cells of microorganisms of public health significance — and those of non-health significance, such as spoilage microorganisms capable of reproducing in food products during their storage, distribution, retail, and holding by the end user.

The rescinded draft guidance recommended that any finished product containing an acidified food ingredient should be an acidified food covered by 21 CFR Part 114. Before 2010, both FDA and the food industry considered a product containing pre-acidified ingredients as an acid food. The acidified ingredient supplier was responsible for filing the acidification process. GMA, supported by the food industry, continues to believe that an acidified food ingredient should be treated as the “predominant acid or acid food” since it is just one more acid component in the final formulation of all acid ingredients. The pre-acidified ingredients will not influence the equilibrium pH of the finished product. There is no distinction, from a food safety and scientific standpoint, between naturally acid ingredients and ingredients that meet the same pH as a result of acidification.

To address the safety of products containing acidified ingredients, the emphasis should be on pH control. The proper measurement of finished equilibrium pH is essential. This will ensure that the acid will be fully diffused throughout the food, especially solids.

FDA recommends that every component of the formula should have a pH that is 4.6 (or lower, if determined by a process authority) within 24 consecutive hours. After the equilibrium pH (4.6 or lower, as required) has been achieved, the likelihood that spores of C. botulinum will germinate and grow is eliminated.

A frequent inquiry GMA receives from food processors of acidified foods is related to water. Under the withdrawn draft guidance, water was treated as a low-acid food. This may be technically true, since pure water has a neutral pH of 7.0, however, noncarbonated bottled water historically has not required a thermal or other C. botulinum spore lethality treatment, and has not been required to be filed as a low-acid canned food (LACF) product. As such, incorporating water into the list of LACF foods to be considered in determining the status of a potential acidified food runs counter to the long-standing precedent of exempting water from this classification. Additionally, water has a minimal buffering capacity and generally acts as a solvent only by providing the medium for monitoring the pH. In other words, just because water has a pH of 7, adding water to any food product will not change the pH of that product.

SALAD DRESSINGS AND SAUCES. Although salad dressings and condiment sauces have historically been excluded from the acidified food regulation, FDA’s draft guidance document suggested that some of these products could come under scrutiny as acidified foods. Salad dressings and condiments with a pH of 4.6 or below are generally considered to be formulated acid foods because they are prepared from a variety of ingredients. Some of the ingredients are low acid, typically in the form of powders, small particulates and liquids. In addition to water-soluble ingredients such as salt, sugar, and flavors, other low-acid ingredients include starch, ground spices, and egg.

The combination of these ingredients with others, such as water, vinegar, and oil, is what makes a salad dressing a salad dressing. These products are not inherently low-acid foods to which acid is added to lower the pH, so their status as acid foods is well justified. Nonetheless, questions continue to arise as to what low-acid ingredients should be considered when evaluating a formula, what constitutes a “small amount” of low-acid ingredients, and what is a significant shift in pH due to the addition of low-acid ingredients.

The nature of many salad dressings and sauces does not allow for a heating step without destroying the integrity of the product. Commercial processors of products with a maximum pH of 4.1 typically rely on a combination of non-thermal factors for inactivation of potential vegetative pathogens and spoilage microorganisms. The parameters include control of pH, acidity as acetic acid in the aqueous phase, hold time after production and others.

An example of a non-thermal Salmonella inactivation process for egg-containing dressings is cited in 21 CFR 101.100. A pH of 4.1 or below with acidity as acetic acid in the aqueous phase of 1.4% or greater and a hold time of 72 hours is considered to be a suitable bactericidal process for Salmonella in an egg-containing dressing.

The excellent public-health safety record of commercially prepared salad dressings and condiment sauces indicates that the inclusion of low-acid liquids, powders, and granules in a dressing or sauce formula does not pose a food safety risk. These ingredients are readily dissolved or hydrate quickly when exposed to acid solutions. Processors who consider their condiment or sauce exempt from the regulation can receive a FDA opinion by voluntarily filing FDA Form 2541e, Food Process Filing for Acidified Method.

BEYOND REGULATION. The focus of acidified foods should be on evaluating the microbiological stability and safety of these products regardless of their regulatory status. Therefore, the proper acidification process and proper application of a well-determined thermal process to control vegetative cells of pathogens are crucial in providing safe acidified foods.

The food safety practices incorporated into process recommendations provided by process authorities have been and continue to be recognized by industry, government, and academia. Thermally processed acidified foods have a good record of food safety and the parameters required to ensure safety and shelf stability are well understood by the food industry. Validation and verification of control measures proposed for acidified foods by the Preventive Controls rule will additionally increase the safety of these products.

The authors: Podolak is GMA senior scientist, processing technologies; Pinkas is principal scientist, microbiology, McCormick & Co.