Food Biochemistry and Food Processing (Simpson/Food Biochemistry and Food Processing) || Microbial Safety of Food and Food Products

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BLBS102-c41 BLBS102-Simpson March 21, 2012 14:25 Trim: 276mm X 219mm Printer Name: Yet to Come

Part 8Food Safety and Food Allergens

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41Microbial Safety of Food and Food Products

J. A. Odumeru

PrefaceIntroductionShelf Life of Foods and Food Ingredients and Food SafetyCategories of Foodborne OrganismsSources of Foodborne PathogensFoodborne Disease Casesand Outbreaks

Foodborne Bacterial InfectionsCampylobacter EnteritisSalmonellosisListeriosisVerotoxigenic Escherichia coli (VTEC) InfectionsFoodborne Parasite InfectionsFoodborne FungiFoodborne Virus Infection

Emerging Pathogens andFood SafetyControl Measures for Microbial ContaminantsFood Safety ProgramsFuture Perspectives on Food SafetyReferences

PREFACEGlobally, food safety issues are of top priorities to the food in-dustry, government food safety regulators, and consumers as aresult of a significant increase in the number of foodborne dis-ease cases and outbreaks reported worldwide in the twentiethcentury. These issues led to the proliferation of several foodsafety programs designed to reduce the incidence of foodborneillness. Although a number of producers and processors haveimplemented a variety of food safety programs, the occurrenceof foodborne illness from emerging and existing pathogens re-mains a challenge to the food industry and food safety regulators.Food safety begins on the farm and continues through process-ing, transportation, and storage until the food is consumed. Foodsafety programs such as Good Manufacturing Practices (GMP),

Sanitation, Food Quality, and Safety Tests, and Hazard AnalysisCritical Control Points (HACCP) are examples of food safetyprograms that are commonly used to control and monitor micro-bial contamination of food.

The three main categories of food safety concerns in the foodindustry include microbiological, chemical, and physical haz-ards. The microbiological hazards are those involving foodbornepathogens; chemical hazards include concerns related to antibi-otics, pesticides, and herbicides; and physical hazards are thoserelated to foreign objects in foods that can result in injury orillness when consumed with foods. Although this chapter ad-dresses issues related to microbial hazards, food safety pro-grams, which provide protection against these three types ofhazards, especially during food processing, will be discussed.Foodborne organisms, sources of microbial contamination offoods and emerging pathogens, will be reviewed in relation tofood safety issues.

INTRODUCTIONFood safety concerns are currently at an all-time high due toworldwide publicity about cases and outbreaks of foodborne ill-ness. These concerns are now of top priority in the political andeconomic agendas of governments at various levels. One of theworst nightmares for food producers or processors is to have thename of their company show up in a news report as the source ofa foodborne illness. Apart from the loss of consumer confidenceand loss of sales, there are also legal aspects about which foodcompanies must be concerned (Odumeru 2002). An estimated76 million cases of foodborne illness per year occur in the UnitedStates, resulting in 325,000 hospitalizations and 5000 deaths(Mead et al. 1999). The economic impact of these illnesses isestimated at $5 billion or more. A number of food safety pro-grams are currently in place in the food industry in an attemptto reduce the incidence of foodborne illness, which has been on

Food Biochemistry and Food Processing, Second Edition. Edited by Benjamin K. Simpson, Leo M.L. Nollet, Fidel Toldra, Soottawat Benjakul, Gopinadhan Paliyath and Y.H. Hui.C© 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.

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788 Part 8: Food Safety and Food Allergens

the rise in the last two decades (Maurice 1994). The increasein the incidence of foodborne disease has been attributed to acombination of factors. These include changes in food produc-tion and processing practices, changes in retail distribution, so-cial changes including consumer preferences and eating habits,lack of experience of mass kitchen personnel, changes in popula-tion demographics, and increases in population mobility world-wide as a result of increases in international trade and travel(McMeekin and Olley 1995, Baird Parker 1994). Furthermore,advances in sciences in the area of analytical methods devel-opment has led to the availability of better detection methodsfor the diagnosis of foodborne illness and a subsequent increasein the number of cases reported. Other factors such as betterreporting systems and increases in the occurrence of emergingpathogens have contributed to the increase in cases of food-borne diseases reported. Issues related to emerging pathogenswill be discussed in a subsection of this chapter. A numberof scientific tools are now available to the food industry andfood safety regulators for implementing food safety programsdesigned to reduce the incidence of foodborne illness. Theseinclude the use of risk assessment of foods and food ingredients,to determine the risks associated with various types of foods un-der certain processing conditions; predictive modeling, whichestimates the growth and survival of pathogens and spoilageorganisms under specified conditions; and rapid methods forscreening foods for quality and safety during and after produc-tion. This chapter will provide an overview of issues related tomicrobial safety of food and food products, food preservationtechnologies, emerging pathogens, food safety programs to con-trol microbial contamination, and future perspectives on foodsafety.

SHELF LIFE OF FOODS AND FOODINGREDIENTS AND FOOD SAFETYThe shelf life of a food product generally refers to the keepingquality of the food. An estimated 25% of the food supplies world-wide are lost as a result of spoilage; hence, it is economicallybeneficial to maintain the quality of food products at variousstages of food production and storage. There are two categoriesof foods in relation to shelf life: shelf stable and perishable.Whether a particular food product is shelf stable or perishabledepends on the intrinsic properties of the food (e.g., pH, wa-ter activity, and structure). Shelf-stable foods usually have lowwater activity, low pH, or a combination of both, while per-ishable foods tend to have high water activity and high pH.The structure or texture of the food is also an important factorin shelf stability. Extrinsic factors such as storage temperature,gaseous atmosphere, and relative humidity also determine theshelf stability of food products (McMeekin and Ross 1996).These intrinsic and extrinsic factors influence the survival andgrowth not only of spoilage organisms but also of pathogenicorganisms in foods. Food spoilage occurs as a result of physicalor chemical changes in the food or of the by-products of spoilagemicroorganisms growing in the food product. Pathogens presentin low levels may not produce identifiable changes in the food;

hence, the presence of pathogens cannot be determined usingnoticeable changes in the food as an indicator.

Although shelf-stable foods are less likely to be implicated infoodborne illness than perishable foods, cross-contamination ofshelf-stable or perishable foods by pathogens can be a source offoodborne illness. A number of preservation applications usedin the food industry are designed to extend the shelf life of thefood product by reducing microbial growth; however, pathogensthat are able to survive or even grow under preservation tech-niques such as refrigeration can cause foodborne illness. Effec-tive strategies for controlling the presence of spoilage and food-borne pathogens in foods should include elimination of sourcesof contamination combined with food preservation technologiessuch as drying, freezing, smoking, curing, fermenting, refriger-ation (Baird-Parker 2000) and modified-atmosphere packaging(Farber 1991).

CATEGORIES OF FOODBORNEORGANISMSMicroorganisms that can be transmitted to humans or animalsthrough food are referred to as foodborne organisms. Thereare three main categories of foodborne organisms: spoilage,pathogenic, and beneficial. Spoilage organisms can grow andproduce physical and chemical changes in foods, resulting inunacceptable flavor, odor, formation of slime, gas accumulation,release of liquid exudates or purge, and changes in consistency,color, and appearance. Also, extracellular or intracellular en-zymes released by spoilage organisms can result in deteriora-tion of food quality. Growth of microorganisms to high numbersis usually required before spoilage becomes noticeable. Hence,control of growth of spoilage organisms is required to impedemicrobial spoilage. The presence of foodborne pathogens infoods in low concentrations can render foods harmful to hu-mans if consumed. Because pathogenic organisms at low levelsmay not produce noticeable changes in foods, consumers maynot have advance warning signals of the danger associated withconsumption of contaminated foods. “Beneficial” or “useful”organisms include microorganisms used in various food fermen-tation processes. These organisms are either naturally present insuch foods or added to produce the desired by-product of fer-mentation. Various types of foods such as fruits and vegetables,pickles, dairy products, meats, sausages, cheeses, and yogurt arecommon types of fermented products involving the use of bene-ficial organisms. Beneficial organisms include organisms in thegroup of lactic acid bacteria, yeasts, and molds. Bacteria speciesfrom 10 genera are included in the group of lactic acid bac-teria. These include Lactococcus, Leuconostoc, Streptococcus,Lactobacillus, Pediococcus, Carnobacterium, Tetragenococcus,Aerococcus, Vagococcus, and Enterococcus. The most importanttype of yeast used for fermentation of food and alcohol is Sac-charomyces cerevisiae. This yeast is used for leavening breadand production of beer, wine, and liquors. It is also used for foodflavor. Non-mycotoxin-producing molds from the genera Peni-cillium and Aspergillus, and some in the Rhizopus and Mucorgenera, have been used for beneficial purposes in food prepara-tion (Bibek 1996).

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41 Microbial Safety of Food and Food Products 789

Figure 41.1. On-farm sources of microbial contamination of water and food products of plant and animal origin. (Adapted from Beuchat 1995.)

SOURCES OF FOODBORNE PATHOGENSIn order to determine and implement effective control mea-sures for pathogens in foods, it is important to identify potentialsources of contamination. Plants and animals are the main sourceof human food supply. The exterior and, in some cases, the inte-rior of plants and animals harbor microorganisms from externalsources such as soil, water, and air. These environmental sourcescontain a wide variety of microorganisms, some of which arepathogenic to man. Contamination of the food supply can occurat various stages of production, processing, transportation, andstorage. For example, fruits and vegetables can be contaminatedat the farm level as well as during harvesting, transportation, andprocessing. Potential sources of on-farm contamination of fruitsand vegetables are summarized in Figure 41.1. Meats can becontaminated at the time of slaughter, processing, and storage.Microbial contamination can come from slaughtered animals,water, equipment, utensils, the slaughterhouse environment, andworkers. Thus, intervention strategies to control microbial con-tamination of the food supply must be implemented at variousstages of food production, processing, transportation, and stor-age, and also at the consumer end of food preparation.

FOODBORNE DISEASE CASESAND OUTBREAKSFoodborne disease in a susceptible host can result from con-sumption of food or water contaminated with pathogenic organ-isms. A single or sporadic case of foodborne illness refers to aninstance when an illness that is unrelated to other cases occursas a result of consumption of contaminated food or water. Anoutbreak, on the other hand, refers to an incident in which twoor more persons become ill after consuming the same food orwater from the same source. The occurrence of a foodborne ill-ness depends on a number of risk factors such as (1) type and

number of pathogenic microorganisms in the food, (2) effectof food product formulation or processing on the viability ofthe pathogen, (3) storage conditions of the food that may pro-mote contamination, growth, and survival of the pathogen, and(4) the susceptibility of the individual to foodborne illness. It isbelieved that the number of reported outbreaks represents only10% of the real incidence of foodborne disease, even in coun-tries with well-established surveillance systems (Baird-Parker2000). Foodborne illness resulting from severe infections suchas hemolytic uremic syndrome, botulism, and listeriosis oftenrequire hospitalization and are more likely to be reported, whileself-limiting foodborne illness such as salmonellosis, campy-lobacteriosis, and S. aureus enterotoxin–related infections areless likely to be reported. It is believed that viral foodborne in-fections account for a large portion of cases of foodborne illness(Caul 2000). However, the extent of the problem on a global scaleis difficult to assess as a result of lack of surveillance data inmost parts of the world, coupled with the fact that most viral in-fections are self-limiting. Although viruses and bacteria-relatedinfections account for the majority of foodborne diseases, cer-tain groups of parasites and fungi are also etiologic agents offoodborne diseases.

Foodborne Bacterial Infections

Several types of foodborne bacterial pathogens are implicatedin foodborne diseases. Examples of bacterial genera most com-monly implicated in foodborne infections, onset and durationof the symptoms of the disease, types of foods that are likelyto be contaminated by these groups of bacteria, and potentialsources of contamination are summarized in Table 41.1. Bac-terial pathogens including Campylobacter, Salmonella, Listeriamonocytogenes, and verocytotoxigenic E. coli are the top causesof bacterial foodborne infections in westernized countries, basedon the number of reported cases (Sharp and Reilly 2000). The

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Table 41.2. The Incidence of the Four Most Frequent Foodborne Disease-CausingPathogens in Canada and the United States

Estimated Cases/Year (Based on Population Ratio)

Bacteria Canada United Statesa

Campylobacter 110,000–700,000 1,100,000–7,000,000Listeria 93–177 928–1767Salmonella 69,600–384,000 696,000–3,840,000Verotoxigenic E. coli (Including

E. coli O157:H7)1600–3200 16,000–32,000

Total 181,3000–1,087,400 1,812,900–10,873,800

aAdapted from Buzby and Roberts 1997.

number of reported cases of Salmonella, Campylobacter, andE. coli O157 increased from 2- to 40-fold between 1982 and 1994(Sharp and Reilly 2000). The increase in the number of caseswas attributed to heightened awareness of foodborne related ill-ness, improved diagnostic methods, and improved reporting andsurveillance procedures. Campylobacter is currently the leadingcause of foodborne disease in the United States and Canada,followed by Salmonella-related infections. The numbers of es-timated cases of foodborne illness per year in the United Statesand Canada countries are listed in Table 41.2. Although thenumber of Listeria monocytogenes–related infections is consid-erably lower than those of other pathogens, foodborne infectionscaused by this organism are characterized by a high case mor-tality ratio, especially in certain high risk groups such as theelderly, the young, immunocompromised individuals, and preg-nant women. Infections caused by E. coli O157:H7 often resultin a high morbidity and mortality rate. For example, complica-tions such as hemolytic uremic syndrome can result in kidneyfailure and death (Riley et al. 1983, Karmali 1989). Sources ofbacterial infections are not limited to contaminated foods; con-taminated water and person-to-person transmission have alsobeen implicated. For example, in a waterborne outbreak ofE. coli 0157:H7 in Walkerton, Ontario, 1700 cases and sevendeaths were reported. This led to changes in the Ontario Drink-ing Water Regulations to include strict water treatment proce-dures and zero tolerance for the presence of coliforms and E.coli in drinking water. Current food safety programs in the foodindustry must now document the use of pathogen-free water infood production and processing facilities.

CAMPYLOBACTER Enteritis

Campylobacter jejuni and C. coli are the species of Campy-lobacter implicated in most Campylobacter enteritis infections.Other species of Campylobacter such as C. lari and C. up-saleusis may also cause Campylobacter enteritis. Symptoms ofCampylobacter infection in humans are watery and/or bloody di-arrhea, abdominal pain, fever, and general malaise. The diseaseis usually self-limiting, and antibiotics are required only whencomplications occur. It is estimated that Campylobacter enteri-

tis accounts for 10% of cases of foodborne illness, and deathis rarely reported. Most cases of this disease are sporadic, andfoods of animal origin, particularly poultry, are largely responsi-ble for most infections. Contaminated fruits and vegetables havealso been implicated in Campylobacter enteritis cases.

Salmonellosis

Salmonellosis infection ranks second in incidence to Campy-lobacter enteritis. This organism is ubiquitous (present every-where) in the environment, especially in the feces of most food-producing animals; hence, a variety of foods are readily con-taminated by this organism. Salmonella are present in animalswithout causing apparent illness. However, certain serotypes ofSalmonella such as S. enteritidis can penetrate poultry repro-ductive organs, resulting in contamination of egg content andposing a health risk to consumers. Salmonellosis symptoms in-clude watery diarrhea, abdominal pain, nausea, fever, headache,and occasional constipation. Hospitalization may be required incases of severe infections. Foods that can become contaminatedwith Salmonella include meat, raw milk, poultry, eggs, dairyproducts, and other types of foods that can become contami-nated with fecal material. An increase in the number of casesof Salmonellosis linked to consumption of contaminated fruitsand vegetables such as bean sprouts, raw tomatoes, melons, andcantaloupes has been reported. In addition to fecal contamina-tion, cross-contamination of foods by Salmonella during foodpreparation can be a source of foodborne illness.

Listeriosis

Listeriosis is caused by Listeria monocytogenes. The ubiquitousnature of this organism contributes to the widespread incidenceof the organism in foods. It is psychrotrophic in nature and isable to grow at refrigeration temperatures. Hence, this organismis of concern in refrigerated foods with extended shelf life. Lis-teriosis infections often result in septicemia and/or meningitis.The case mortality ratio for Listeriosis infections is much higherthan those of Salmonella, Campylobacter, and E. coli 0157:H7infections. An estimated 500 deaths associated with Listeriosis

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are reported annually in the United States. Individuals most sus-ceptible to Listeriosis include the elderly, the young, immuno-compromised patients, and pregnant woman. A wide variety offoods including processed meats, milk and dairy products, fruits,and vegetables have been implicated in a number of Listeriosesoutbreaks. In 1999, a multistate outbreak involving 1000 casesof Listeriosis in the United States was linked to consumptionof contaminated hot dogs and delicatessen meats, resulting ina recall of 35 million pounds of these food products (MMWR1999).

Verotoxigenic ESCHERICHIA COLI (VTEC)Infections

Verotoxigenic Escherichia coli (VTEC) belonging to the O157serogroup is the most common VTEC serogroup implicated infoodborne disease outbreaks. This organism was first recog-nized as a cause of hemorrhagic colitis in 1982. VTEC O157and serogroups O5, O26, and O111 are of high prevalence in fe-ces of healthy cattle. Thus, foods of animal origin such as meat,milk, and dairy products can be contaminated with these or-ganisms. Other types of foods such as salads, vegetables, fruits,sandwiches, and cooked meat can be contaminated during prepa-ration. Contaminated water can also be a source of infection bythis organism. The majority of food- and waterborne outbreakshad links with contamination of fecal origin. Infection by VTECcan result in hemorrhagic colitis (HC) and hemolytic uremicsyndrome (HUS), abdominal pain, and watery diarrhea (bloodyor nonbloody). The HC symptoms may lead to complicationsof the HUS and subsequent renal failure. Although HUS canoccur in any age group, children are more susceptible (Karmali1989). In adults, 50% of thrombocytopenic purpura (TP) casesare caused by HUS.

Other bacterial foodborne infections can occur as a result of in-gestion of food contaminated with Staphylococcus aureus toxin,Clostridium perfringens, Clostridium botulinum toxin, Shigellaspp., Yersinia enterocolitica, Brucella spp., Vibrio cholera, Vib-rio paraheamolylicus, and Bacillus cereus enterotoxin.

Foodborne Parasite Infections

Foodborne parasite infections are caused by certain groups ofprotozoa. It is believed that foodborne infections related to par-asites are underreported by an estimated factor of 10 or more(Casemore 1991), and the etiological agent of foodborne out-breaks is identified in less than 50% of the cases (Bean et al.1990, Cliver 1987). Parasites commonly associated with food-borne disease and possible food and water sources are listed inTable 41.3.

Cryptosporidium parvum is the species of Cryptosporidiumassociated with infection in humans (Current and Blagburn1990). It is a common cause of gastrointestinal infections in im-munocompromised individuals and is an opportunistic pathogenassociated with infections in patients with acquired immunedeficiency syndrome (AIDS), but it affects healthy people aswell. Although drinking water contaminated with human or an-imal feces is the usual source of transmission of this organ-

Table 41.3. Foodborne Parasites, Fungi, and VirusesAssociated with Food- or Waterborne Illness

Pathogen Sources of Pathogen or Toxin

ParasitesCryptosporidium Contaminated surface water or

foods in contact withcontaminated water

Cyclospora Raspberry, mesculun lettuce, andbasil

Sarcocystis Raw or undercooked meatToxoplasma Raw or undercooked meatGiardia Contaminated surface water

FungiPenicillium Mycotoxins in apple juice, walnuts,

corn and cerealsAspergillus Mycotoxins in groundnuts, corn,

figs and tree nutsFusarium Mycotoxins in cereals, corn, wheat

and barleyViruses

Hepatitis A and E Contaminated water, fruits andvegetables, raw shellfish, rawoysters

Norwalk/Norwalk–like viruses

Variety of foods and water

Calcivirus Water and contaminated foodsAstrovirus Water and contaminated foods

ism to humans, epidemiological links between the consump-tion of contaminated foods such as raw sausage, offal, andraw milk and cryptosporidiosis have been reported (Casemore1990, Casemore et al. 1986). The largest outbreak of waterbornecryptosporidiosis was reported in Milwaukee, Wisconsin, with403,000 persons ill. Reported outbreaks in most countries areassociated with contaminated drinking water or contaminatedswimming pools.

Cyclospora is an emerging pathogen, which causes diarrhealinfections in humans. The first reported outbreak of Cyclosporainfection occurred in 20 US states and two provinces in Canada,Ontario and Quebec, during the months of May and June, 1996,and April and May, 1997. Consumption of contaminated im-ported raspberries was implicated in many of these outbreaks(Herwaldt and Ackers 1996, Herwaldt and Beach 1997). Con-taminated mesclun lettuce and basil have also been linked toCyclospora outbreaks (MMWR 1997).

Sarcocystis is another coccidian parasite, which is prevalentin livestock. Human infection occurs as a result of ingestion ofraw or undercooked meat containing mature sarcocysts (Tenter1995).

Toxoplasma gondii is an intracellular parasite, which is preva-lent in man and animals (Fayer 1981). Ingestion of raw or un-dercooked meat from livestock and game animals is often im-plicated in human toxoplasmosis infections. Another parasitecommonly implicated in food and waterborne illness is Giardia.

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Outbreaks of food and waterborne illness have been reported inthe United States and the United Kingdom (Craun 1990, Porteret al. 1990). Infection with this parasite is associated with unsan-itary conditions, and contaminated water is the most commonsource of infection.

Foodborne Fungi

Fungi most commonly associated with foodborne intoxica-tions are Penicillium, Aspergillus, and Fusarium. The types offoods that may contain mycotoxin contamination are listed inTable 41.3. A foodborne fungi outbreak associated with con-sumption of corn contaminated with Aspergillus flavus was re-ported in India. The outbreak involved 1000 cases and 100 deaths(Krishnamachari et al. 1975). Mold growth can occur in foodsstored under high temperature or humidity, resulting in the pro-duction of mycotoxin, which can be harmful to humans.

Foodborne Virus Infection

Viruses from human fecal origin can result in illness if ingestedwith food or water. Food or waterborne viruses commonly as-sociated with human illness are listed in Table 41.3. Viral gas-troenteritis is caused by Norwalk-like viruses and in some casesby the calicivirus and astrovirus groups. The symptoms ofteninclude acute but short self-limiting episode of diarrhea andvomiting. The viruses can be transmitted from person to personvia contaminated utensils and foods. Foodborne viral hepatitisin humans is caused by the hepatitis A or hepatitis E virus. Theonset of hepatitis may be preceded by anorexia, fever, fatigue,nausea, and vomiting. Infected individuals shed the organism infeces, which if allowed to contaminate food or water, can resultin person-to-person transmission (Caul 2000).

EMERGING PATHOGENS ANDFOOD SAFETYEmerging infectious diseases have increased in the last twodecades and are likely to increase in the future. Hence, thecharacteristics of the etiologic agents of these diseases mustbe considered when designing control measures to ensure foodsafety. There are two types of emergence: true emergence andreemergence. A true emergence involves the occurrence of mi-crobial agent not previously identified as a public health threat. Areemergence involves the occurrence of a microbial agent caus-ing disease in a new way not previously reported or the reemer-gence of a human disease after a decline in incidence. Emergencemay be due to the introduction of a new agent, to recognitionof an existing disease that was not previously detected, or toenvironmental pressures resulting in occurrence of a pathogenthat can cause human disease. For example, the occurrence ofenterohemorrhagic E. coli O157:H7 as a pathogen in 1982 isbelieved to be due to introduction of a new agent. The organismwas involved in two outbreaks that year in the United States,and these outbreaks were associated with consumption of un-dercooked hamburgers from a fast-food restaurant chain. Severalcountries worldwide have reported outbreaks of infection caused

Table 41.4. Emerging Pathogens and SuspectedCauses of Emergence

Pathogens Cause of Emergence

Salmonella DT104 Resistance to antibioticsE. coli O157:H7 Development of a new pathogenCyclospora cayetanensis Development of a new pathogenCryptosporidium parvum Development of a new watershed

areasHepatitis E virus Newly recognizedNorwalk Virus Increased recognitionAeromonas Spp. Immunosuppression and

improved detectionC. jejuni Increased recognition,

consumption of uncookedpoultry

L. monocytogenes Increased awarenessHelicobacter pylori Increased recognitionVibrio vulnificus Increased recognition

by this organism. The appearance of Salmonella typhimuriumphage type 104 is another example of a new agent. Increasesin the use of antibiotics in humans and animals may have pro-vided the environmental pressures resulting in the occurrenceof Salmonella typhimurium phage type 104 with multiresistanceto five antibiotics: ampicillin, chloramphenicol, streptomycin,sulphonamides, and tetracycline. This multiresistant character-istic leaves little choice of antibiotics for treatment of diseasecaused by this organism. The occurrence of Listeria monocyto-genes as a foodborne agent is an example of reemergence. Theorganism is a well-known infectious agent; however, its role as afoodborne organism was not detected until the early 1980s. Ex-amples of emerging foodborne pathogens and possible causes ofemergence are provided in Table 41.4. The challenge posed bythe appearance of emerging pathogens is that these organismsmay not always behave as traditional pathogens. Therefore, newcontrol measures to ensure that foods are free of these pathogensmay be required.

CONTROL MEASURES FOR MICROBIALCONTAMINANTSA combination of factors is normally responsible for occurrenceof an incident of foodborne illness. The pathogen must firstreach the food involved; the organism must survive until food isingested; in many cases, the organism must multiply to an infec-tious level or produce toxins; and lastly, the host must be suscep-tible to the level of organisms ingested with the food. Controlmeasures to ensure food safety include (1) prevention of con-tamination of foods by pathogenic organisms (2) inhibition ofgrowth or elimination of pathogens in foods and food products.The first stage of control measures is to prevent contamination offood animals and plants during the production stage. Productionpractices such as the use of manure and other organic fertil-izer materials can provide the vehicle for contamination of food

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crops; hence, it is important to ensure that this type of fertilizer ispathogen-free prior to use. The second stage of control measureis to prevent contamination and growth of pathogenic organismsduring harvesting and transportation of food products. It is gen-erally believed that control of microbial contamination early inproduction is more effective than control measures applied at alater stage of production. However, in cases when the presenceof pathogens cannot be eliminated during the production stage,processing procedures that are designed to control the presenceof pathogens must be implemented. A combination of intrinsicfactors, (i.e., factors associated with the properties of the food)and extrinsic factors (i.e., factors associated with external con-ditions) is often used during processing and storage to controlmicrobial growth or survival in foods (Bibek 1996). Intrinsicfactors such as the pH, water activity, and food components canpromote or inhibit microbial growth or survival. These prop-erties can be used in combination with extrinsic factors suchas heat, preservatives, irradiation, and storage conditions (e.g.,refrigeration, relative humidity, and gaseous atmosphere).

Currently, there are several food preservation technologiesavailable for controlling microbial growth and survival. Themost commonly used technologies for controlling microbialgrowth include application of low temperatures such as refrig-eration or freezing, reduction of water activity of the food bydrying, curing with salt or increased sugar level, pH reductionby acidification or fermentation, use of food preservatives, andmodified atmosphere techniques. Other preservation technolo-gies designed to inactivate foodborne organism include heattreatment such as sterilization, cooking, retorting, pasteuriza-tion, irradiation, and the use of hydrostatic pressure and pulselight. Also, use of packaging materials and adequate sanitationof the food production or processing environment can be used tolimit entry of microorganisms into the food product and preventrecontamination of processed foods (Gould 1989, Hall 1997).The use of a combination of preservation techniques, often re-ferred to as the hurdle concept, can be very effective in con-trolling microbial growth. A combination of suboptimal levelsof the growth-limiting factors can be very useful where higherlevels of one of the factors can be detrimental to the quality ofthe product. The most important hurdles used in food preserva-tion include high or low temperature, water activity (aw), redoxpotential (Eh), acidity (pH), preservatives such as sulfite, nitrite,and sorbate, and the use of competing microorganisms such aslactic acid bacteria. The application of an appropriate combina-tion of these hurdles can improve the microbial stability, sensoryand nutritional qualities, and safety of the foods.

FOOD SAFETY PROGRAMSTraditional approaches to controlling the safety and quality offoods involve inspection of foods after production or processingfor compliance with general hygienic practice, and where appro-priate, foods are sampled for laboratory testing. This approachdoes not ensure food safety since reliance on visual inspectionand testing of finished products cannot guarantee the absence ofharmful pathogens in food. A more effective food safety con-trol program, called the hazard analysis critical control point

(HACCP) program, was introduced to the food industry in theearly 1970s, and various food safety regulations and trade bodiesworldwide endorsed its use as an effective and rational approachto assurance of food safety. HACCP is a systematic approachto hazard identification, assessment, and control. The benefitsof the HACCP approach to ensuring food safety include thefollowing:

� The food industry has a better proactive tool for ensuringthe safety of foods produced.

� Potential food safety problems can be detected early.� Food inspectors can focus more on verifying plant controls.� More effective use is made of resources by directing atten-

tion to where the need is greatest.� A significant reduction in the cost of end product testing is

achieved.

There are seven key principles of HACCP. Principle No. 1includes hazard analysis to identify the microbiological, chem-ical, and physical hazards of public health concern. Raw ma-terials processing procedures, including packaging and storage,are assessed for microbiological hazards. The second principleis to determine the procedures or points in the food operationwhere hazards can be controlled effectively. These are calledthe critical control points (CCPs). The third principle includesthe establishment of critical limits that separate acceptable fromnonacceptable limits. The fourth principle involves the devel-opment of a system to monitor the CCPs so that the limits arenot exceeded. The fifth principle is to determine what correctiveactions to take when the CCPs are exceeded. The sixth principleincludes the establishment of procedures for verifying that theHACCP program is working as expected. The seventh princi-ple involves the documentation procedures and records for allaspects of these six principles. These HACCP principles havereceived worldwide recognition, by governments and the foodindustry. Many industrial organizations have adopted this foodsafety program as a means of controlling food safety hazards.

One of the most successful food safety programs at the con-sumer level is the FightBac program developed by the Partner-ship for Food Safety Education (PFSE), formed in 1997. Thisnonprofit organization provides education on safe handling offood to the public. The key features of the information on safehandling of food in the FightBac program are summarized inTable 41.5. Further information on this program can be foundin the FightBac website (www.fightbac.org). Implementation ofthese safe food-handling procedures by consumers can preventthe occurrence of foodborne illness.

FUTURE PERSPECTIVES ONFOOD SAFETYFoodborne disease is preventable, provided control measuresto prevent contamination of the food supply are implementedat various stages of the food chain, from the farm to the pointof consumption. On-farm food safety programs include controlmeasures for preventing contamination of plants, animals, andplant and animal products that are produced for human consump-tion. Implementation of effective environmental sanitation, good

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Table 41.5. Four Simple Steps for Consumers to Ensure Food Safety (FightBac!TM)

Clean: Wash hands and surfaces often� Wash your cutting boards, dishes, utensils, and counter tops with hot soapy water after preparing each food item and before you

go onto the next food� Use plastic or other nonporous cutting boards� Consider using paper towels to clean up kitchen surfaces

Separate: Don’t cross-contaminate� This is especially true when handling raw meat, poultry, and seafood� Never place cooked food on a plate that previously held raw meat, poultry, or seafood

Cook: Cook to proper temperatures� Use a clean thermometer that measures the internal temperatures of cooked foods to make sure meat, poultry, casseroles, and

other foods are cooked all the way through� Cook roasts and steaks to at least 145◦F. Whole poultry should be cooked to 180◦F for doneness� Cook ground beef, where bacteria can spread during processing, to at least 160◦F� Don’t use recipes in which eggs remain raw or only partially cooked

Chill: Refrigerate promptly� Refrigerate or freeze perishables, prepared foods, and leftovers within 2 hours or sooner� Never defrost at room temperatures. Thaw food in the refrigerator, under cold running water, or in the microwave. Marine foods

in the refrigerator� Divide large amounts of leftovers into small, shallow containers for quick cooling in the refrigerator

Source: FightBac!, Partnership for Food Safety Education. Available at www.fightbac.org.

manufacturing practices (GMPs) and hazard analysis criticalcontrol points (HACCP) programs are key control measures formicrobial, chemical, and physical hazards, not only at the farmlevel, but also during food processing, transportation, storage,and final preparation of foods prior to consumption. Further-more, education and training of producers, processors, retailers,restaurant personnel, and consumers are important in the im-plementation of control measures to ensure the safety of foodsconsumed. Also, adequate inspection of food processing facil-ities and operations is very important to ensure that sanitation,GMP and HACCP protocols are being followed on a consistentbasis. In order to implement a HACCP program successfully,the management of food operations must be committed to theprogram, by being aware of the benefits the program offers, andbe prepared to invest time and money into the program. The useof microbiological testing as a verification tool for food safetyprograms including HACCP is important in providing evidencethat indeed the control measures in place are effective. Finishedproduct testing alone must not be relied on as means of ensuringfood safety. The application of rapid methods for microbiologi-cal tests provides a useful tool for ensuring production of a safefood product at various points in the HACCP implementation.Microbiological tests can be performed for (1) the raw materialsrequired for processing, (2) monitoring critical control points,and (3) HACCP verification. The reliance on testing of finishedfood products alone is a thing of the past. The challenge to foodmicrobiologists now is to develop on-line food safety testingtools that can be used during food production. The limitation ofcurrent rapid tests for foodborne pathogens is that they require24 hours or more to complete because of the requirement for am-plification of pathogen numbers to detectable levels. The ability

to detect pathogens at very low levels within seconds, minutes,or in less than 24 hours is an important future development forfood microbiologists.

The likelihood of future increases in the incidence of food-borne illness is high as a result of increases in the numberof susceptible aging populations, the treatment of disease withimmunosuppressing drugs, and increases in the availability ofready-to-eat foods requiring no further processing prior to con-sumption. Unless steps are taken to implement food safety pro-grams, which can reduce microbial contamination of foods atall levels of food production, processing, and retailing, and toeducate restaurant personnel and consumers about the safe han-dling of foods, outbreaks of foodborne illness will continueto occur.

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