Salmonella Control in Commercial Baking: Kill-Step Validation

Overview of the U.S. Baking Industry

The baking industry in the United States is older than the country itself, and a number of flour mills in the American colonies operated bakeries (Albion & Williamson, 1944). Many of the baked goods produced by these early bakeries—especially bread products—bore little resemblance to their modern, enriched counterparts. As Albion and Williamson (1944) report, "A considerable part of their exports being bread, probably mainly a 'hardtack' that would not deteriorate on long sea voyages" (p. 447). Over time, the American baking industry became more specialized, with one sector focusing on pastries, cakes, pies, and breads, while a second sector produced biscuits and crackers (Albion & Williamson, 1944).

The biscuits and cracker sector was the first to introduce large-scale factory production, largely because its products were less perishable and could be distributed over larger geographic regions (Albion & Williamson, 1944). At the turn of the twentieth century, American bakeries in this sector began to form strategic alliances and large corporations became commonplace. Albion and Williamson note that "In 1898 the National Biscuit Company [NBC] was formed by the merger of four large companies. The new company, it was claimed, would control the cracker and biscuit trade from the Atlantic to the Rockies, operating 139 plants and about 90% of the total capacity of the industry" (p. 447).

NBC applied improved packaging methods and innovative marketing strategies to grow its market share rapidly. By 1900, it was using more than two million barrels of flour annually and had plans to mill its own flour (Albion & Williamson, 1944). The other baking sector—specializing in perishable goods such as breads, pies, cakes, and pastries—benefited from manufacturing improvements introduced during World War I, which helped it develop commercial products, especially preservative-enhanced breads, that enjoyed widespread popularity (Albion & Williamson, 1944).

By 1940, the U.S. federal government, concerned over the malnourishment that had adversely affected the American population during the Great Depression, took action. At least 13% of the initial million men assessed by draft boards in 1940 were refused active duty service due to malnourishment and associated symptoms (Wonder Bread, 2012). According to the editors of The Wilson Quarterly, "It dawned on the government to spike the most ubiquitous items in American pantries with vitamins. Thiamin, niacin, iron, and eventually riboflavin became banner ingredients of enriched bread" (Wonder Bread, 2012, p. 66).

To ensure public receptivity to enriched bread, the U.S. Department of Agriculture partnered with baking industry researchers in 1952 to launch what has been termed the "Manhattan Project of bread" (Wonder Bread, 2012, p. 66). The goals of this public-private partnership were twofold: (a) to identify American consumer preferences for white bread taste, texture, and appearance, and (b) to develop manufacturing processes capable of producing large quantities of bread rapidly (Wonder Bread, 2012). The findings were based on exhaustive testing of 600 American families in Rockford, Illinois. Most consumers preferred "extremely fluffy bread," likely because this quality was widely regarded as a sign of freshness, and also preferred bread that was two-and-a-half times sweeter than the typical product of the day (Wonder Bread, 2012).

Researchers also identified a new method for fermenting yeast that significantly reduced the rising time required for bread products and introduced methods for strengthening gluten strands to withstand more rigorous automatic production (Wonder Bread, 2012). As the editors of The Wilson Quarterly conclude, "Four years and almost one hundred thousand slices of bread later, the prototypical loaf of enriched white bread was born" (Wonder Bread, 2012, p. 66). By 1962, average American consumers were eating one-and-a-half pounds of this newly enriched bread product each week, providing between 25% and 30% of their requisite caloric intake (Wonder Bread, 2012).

Today, companies in the American baking industry produce an enormous array of products, including fresh and frozen bread, cakes, pies, and doughnuts (Bakery business, 2016). Major competitors include Flowers Foods and McKee Foods. Approximately 2,800 commercial bakeries account for a combined annual revenue of approximately $36 billion, together with around 6,000 retail bakeries generating approximately $3.8 billion (Bakery business, 2016). Today, the industry generates more than $102 billion in direct economic activity each year and employs more than 706,000 highly skilled workers; the aggregated total economic impact, taking into account the multiplier effect of supplier and induced spending, is estimated at nearly $310 billion a year (Baking industry economic impact study, 2016).

The U.S. baking industry has an enormous impact on the American economy, generating approximately $311.0 billion in total economic output, or about 2.1% of the country's GDP (Baking industry economic impact study, 2016). According to the American Bakers Association (ABA), bakers, product wholesalers, and retailers directly or indirectly employed approximately 1.76 million Americans in 2010. Individuals employed in the U.S. baking industry earned more than $90.2 billion in wages and benefits in 2015 and paid $38.5 billion in direct federal, state, and local taxes—a figure that does not include state and local sales taxes paid on baked goods (Baking industry economic impact study, 2016).

Demand for bakery goods is projected to increase at a yearly rate of approximately 0.6% over the next five years, reaching a total of nearly $40 billion (Bakery business, 2016). The U.S. Small Business Development Centers (SBDC) reports that "Consumers are expected to continue to trend toward healthy eating and increase demand for items like fortified breads, gluten-free loaves and sprouted and organic sweets" (Bakery business, 2016, p. 3). External competition has increased over the past five years and imports will continue to grow at an annualized rate of 7.1%; however, growing demand outside the country is expected to increase exports by 9.8% per year over the next five years (Bakery business, 2016).

In 2012, there were approximately 167,600 baker jobs in the United States, with about 6% of bakers self-employed (Bakery business, 2016). Industry analysts project a 6% increase in the number of bakers between 2012 and 2022, though this rate is below the average for all occupational types. Innovations in manufacturing and mass production methods are also expected to limit future job growth (Bakery business, 2016).

Changing consumer preferences also continue to shape the industry. Fully 50% of American consumers currently report that high fiber content in prepared cakes and pies is important to them (Zegler, 2014). About 58% express increased demand for bakery goods that are fresher and higher in protein content. As Zegler (2014) emphasizes, "Not only do consumers want to know what's inside their products, they want to know how it got there and more about the company that made it" (para. 3). The U.S. baking industry thus faces both significant challenges and opportunities going forward.

Salmonella as a Food Safety Threat in Bakeries

Today, Salmonella bacteria are the most frequently reported source of foodborne illness in the United States (Claudio, 2012; USDA food safety information, 2016). Salmonella are gram-negative pathogens that can cause diarrheal illness in infected humans (USDA food safety information, 2016). According to the FDA, "[Salmonella] are microscopic living creatures that pass from the feces of people or animals to other people or other animals. The Salmonella family includes over 2,300 serotypes of bacteria which are one-celled organisms too small to be seen without a microscope" (USDA food safety information, 2016, para. 4). Two serotypes—Salmonella Typhimurium and Enteritidis—are the most commonly encountered in the U.S. and cause fully 50% of human infections (USDA food safety information, 2016).

Salmonella does not typically alter the smell, taste, or appearance of food products, making its detection particularly difficult (USDA food safety information, 2016). All raw foods of animal origin—including many commonly used as baking ingredients such as eggs, milk, and other dairy products—are potential carriers. Although Salmonella is most commonly associated with raw poultry and beef processing, bakeries can also experience contamination through the constituent ingredients used in baked goods, and outbreaks have occurred historically and remain a salient threat even in highly developed nations (Claudio, 2012).

As recently as 2002, two deaths and hundreds of illnesses caused by Salmonella poisoning in London were traced to a single egg supplier (Harris & Wright, 2002). A follow-up report found that "more than 350 people have been taken ill in Britain in six salmonella outbreaks linked to eggs since August 2002 and two people in the North West have died. Many of the cases were traced back to bakeries which used raw eggs in icing and desserts" (Poulter, 2002, p. 23).

These challenges are compounded by political and institutional obstacles. One industry analyst observes:

"At the beginning of the twenty-first century, efforts to prevent microbial contamination of the food supply continue to be held hostage to industries obstructing intervention, agencies competing for scarce resources, inspectors defending obsolete job descriptions, courts defending obsolete laws, and a Congress more anxious to protect the sources of campaign contributions than the health of the public." (Nestle, 2010, p. 137)

Salmonella is responsible for more human deaths than any other foodborne pathogen in the United States (Nestle, 2010). Approximately 1.2 million American consumers suffer from Salmonella poisoning each year, and the pathogen is highly resistant to conventional cleaning and sanitation methods (Nestle, 2010). Bakery goods can have Salmonella spp. introduced through a wide array of constituent ingredients such as eggs, milk products, flour, milk chocolate, coconut, peanut butter, fruit, spices, and yeast flavorings (Channaih, 2015). If commercial bakery products are improperly cooked, the presence of Salmonella spp. can represent a significant public health threat (Channaih, 2015).

The FDA's overarching concerns with respect to Salmonella in baked goods include the following: (1) Salmonella cannot grow in low-moisture foods and environments but can survive; (2) survival can occur for long periods of time; (3) low-moisture foods tend to have longer shelf lives; (4) heat resistance increases under low-moisture conditions; (5) low numbers of Salmonella can cause illness; and (6) if low-moisture ingredients or foods are rehydrated during manufacturing or preparation, bacteria can grow rapidly, significantly increasing the health risk to consumers (Channaih, 2015).

Some factors that can cause Salmonella contamination in the low-moisture food environments typical of commercial bakeries include poor building and equipment design, poor quality ingredients, poor cleaning and sanitation practices, poor pest management practices, and lack of validation (Channaih, 2015). Even airborne dust in a food manufacturing facility can be a source of Salmonella contamination. The bacteria are capable of adapting to extreme environmental conditions, including pH (can survive at pH 3.8 to 9.5, optimal 6.5 to 7.5), low water activity, and varied temperature conditions (2–54°C, optimal 35–37°C) (Channaih, 2015). When the water activity (denoted as a_W) of baked goods is reduced, Salmonella growth is correspondingly reduced; however, the surviving bacteria are actually strengthened by this process and their survival rates are significantly increased (Channaih, 2015). According to one food safety expert, "The survival [of Salmonella] is affected by nutritional composition of the products: Salmonella showed highest resistance in low water activity and high fat foods. The location (internal vs. external) of Salmonella cells in a product is also critical for its long-term survival" (Channaih, 2015, p. 4).

Controlling Salmonella in Low-Moisture Baking Environments

There are several steps that commercial bakeries can take to help control Salmonella in low-moisture foods and environments. These include: considering points of entry for microorganisms; understanding the factors that influence Salmonella survival in low-moisture foods and environments; applying sound building and equipment design; effectively implementing preventive controls, prerequisite programs, Good Manufacturing Practices (GMPs), and HACCP; conducting regular inspection and auditing; taking effective corrective action; and performing process validation or kill-step validation (Channaih, 2015).

Commercial bakeries should also remain vigilant concerning the numerous possible entry points for Salmonella, including raw materials and ingredients, air, water, personnel, contact materials and surfaces, and pests (Channaih, 2015). In most cases, ingredients are the primary source of contamination. Ingredients are increasingly being tested by food processors and their customers. In most cases, positive finished-product tests have been traced back to positive ingredient tests and subsequent recalls. Bakeries should request certificates of analysis from suppliers and conduct testing where necessary.

Pest management is another critical control area. Proven control strategies include effective GMPs, sound personnel practices, appropriate building and equipment design, production and process controls, sanitation and cleaning practices, proper storage and distribution, and a robust environmental monitoring program (EMP) (Channaih, 2015). Microorganisms are generally introduced into the food processing environment through raw materials, pests, air, water, and employees. To the extent that contamination levels are allowed to increase unchecked, or that inadequate sanitation procedures are used, Salmonella can become established and cause foodborne illness. As Channaih (2015) advises, "A substantial amount of foodborne illness outbreaks results from poor environmental controls and/or hygiene practices. Hence, it is critical to maintain and monitor the hygienic environment in the food processing facility" (p. 4).

Implementing an Effective Pathogen Environmental Monitoring Program

A useful strategy for mitigating the risk of Salmonella contamination is the implementation of a pathogen environmental monitoring (PEM) program. An effective PEM program can help mitigate the risk of Salmonella spp. contamination in both production and post-production environments when included as an integral element of a food production facility's hazard analysis and critical control points (HACCP) plan (Preventing Salmonella recontamination, 2015). An effective PEM program will measure the overall effectiveness of sanitary design, personnel practices, and operational methods.

The PEM can be used to verify that cleaning and sanitizing procedures are (a) keeping indicator organisms and any organisms of particular concern in check and (b) assessing the risks posed by the pathogen of concern (Preventing Salmonella recontamination, 2015). It is important to note, however, that even the most rigorous PEM program is insufficient on its own to ensure food safety. Channaih (2015) emphasizes that environmental monitoring programs are "not designed to validate the effectiveness of cleaning and sanitizing methods, but is more focused on validating cleaning and sanitizing frequencies, and all the programs of the Good Manufacturing Practices (21 CFR)" (p. 5).

Conclusion and Recommendations

Complex problems typically require complex solutions, and this is certainly the case with mitigating the threat of foodborne illnesses in the United States today. With a multi-billion dollar economic impact and as a provider of a mainstay of the American diet, the U.S. baking industry is vitally important to the nation's best interests. The research was consistent in showing that, despite the challenges and complexity of controlling microscopic pathogens such as Salmonella spp., the American baking industry has achieved a solid track record of success in mitigating this serious threat to public health.

Nevertheless, the research also consistently emphasizes that Salmonella is the leading source of foodborne illness, and the pathogen is not expected to disappear anytime soon. Even if Salmonella spp. were eliminated, other microscopic pathogens such as Clostridium botulinum would still represent significant threats, and the baking industry must remain vigilant and proactive. While the kill-step validation process is complex and time-consuming, and must be performed by experienced microbiologists and statisticians with appropriate containment and laboratory facilities, it is the only proven method that can provide evidence that mitigation strategies are working as intended.

The effectiveness of a kill-step validation study also requires: (a) industry-specific GMPs, (b) an effective and timely HACCP program, (c) a sanitation program, (d) effective employee hygiene practices, (e) a comprehensive pest control program, and (f) good post-process hygiene handling procedures (Channaih, 2015). Following the establishment of pathogen controls, it is also essential to conduct process validation to ensure those controls are performing as required.

A number of recommendations emerged from the review of the relevant literature and industry-specific resources. Most importantly, the American Bakers Association should develop and disseminate evidence-based kill-step validation strategies to the more than 700 baking facilities and baking company suppliers it represents before the U.S. Congress. In recent years, significant improvements have been made to food production, handling, and distribution, but keeping food products safe from pathogen contamination remains an ongoing challenge. It is therefore vitally important for the entire industry to develop, implement, and administer effective scientific validation processes to ensure that pathogens are actually being destroyed through cooking or other preventive measures. Although every commercial bakery is unique, they all share this common need.

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