Food Preservation and Foodborne Microbial Diseases

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Chapter 29

• Food Preservation and Foodborne Microbial Diseases

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Food Spoilage

• Food spoilage any change in the appearance,
  smell, or taste of a food product that makes it
  unacceptable to the consumer.
• Spoiled food is not necessarily unsafe to eat,
  but pathogenic organisms can cause food spoilage.
• Food spoilage results in economic loss to
  producers, distributors, and even consumers.
• Since foods are organic they provide nutrients
  for the growth of a large variety of
  chemoorganotrophs.

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Food Spoilage (cont.)

• Based on water content, foods can be classified
  as highly perishable, semiperishable, or
  nonperishable.
• Enteric bacteria, ex. Salmonella, Shigella,
  Escherichia, often contaminate meat during the
  slaughtering process.
• Lactic acid bacteria are the most common
  microorganisms in dairy products and are the
  major spoilers of milk and milk products.
• Pseudomonas spp. Are widely involved in the
  spoilage of fresh foods.

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Food Preservation - Temperature

• Temp. Generally the lower the better to prevent
  food spoilage, although psychrotolerant
  microorganisms can survive and grow at
  refrigerator temps.
• Refrigerators 4C ? temporary storage.
• Freezers -20C ? storage for weeks to months.
• Low temp. freezers or dry ice -80C ? long-term
  storage, expensive.

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Acidity

• pH 5 or less inhibits the growth of most spoilage
  organisms, ex. pickling (reduces water
  availability).
• Pickling vinegar sugar or salt ? cucumbers,
  meats, fruits.
• Fermented foods, ex. sauerkraut (cabbage),
  yogurt, cheese, sour cream are acidic due to
  lactic acid bacteria, acetic acid bacteria, etc.

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Water Availability

• Preserve foods by reducing water
  activity/availability by
• Freeze-drying lyophilization, ex. milk, meat,
  fruit, etc.
• Addition of salt or sugar, ex. jams, jellies,
  sausage, ham.

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Canning

• Canning food is sealed in a container such as a
  can or glass jar and heated to kill all living
  organisms, or at least to ensure that there will
  be no growth of residual organisms.
• Acidic foods should be heated to 100C, whereas
  nonacidic foods should be heated to 121C.
  Properly canned foods may not be sterile b/c
  heating them for the time required might alter
  the foods taste and nutritional value.
• Since some of the anaerobic organisms that can
  grow in cans are from the genus Clostridium, food
  from a can that is visibly altered, ex. bulged
  can, should not be eaten.

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Chemical Food Preservation Irradiation

• Ex. of chemical food preservatives sodium
  benzoate, sulfites, sodium nitrate, formaldehyde
  (from food-smoking process). Some of these are
  controversial due to potential carcinogenic and
  mutagenic properties.
• Irradiation involves the use of ionizing
  radiation to reduce contamination by bacteria,
  fungi, and insects, ex. meat, dried spices, fresh
  fruits and vegetables.

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Foodborne Diseases and Microbial Sampling

• Food Poisoning (or intoxication) disease that
  results from ingestion of foods containing
  preformed microbial toxins, ex. Clostridium
  botulinum, S. aureus.
• Food infections active infections resulting
  from ingestion of pathogen-contaminated food.
• Microbial sampling of foods includes conducting
  nucleic acid probe tests or inoculation onto
  enriched or selective media to detect pathogens.

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Staphylococcal Food Poisoning

• Heat-stabile enterotoxins cause gastroenteritis
  (nausea, vomiting, diarrhea).
• 185,000 cases/yr. in the U.S.
• Custard- and cream-filled baked goods, poultry,
  meat, etc. are commonly involved.
• Detected by ELISA or growth methods.
• Disease is usually self-limiting and treated for
  dehydration caused and not treated with
  antibiotics since the disease is a result of the
  toxin and not an active infection.

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Clostridial Food Poisoning

• Botulism exotoxin causes paralysis. Ingestion of
  a small amount is dangerous and can be fatal.
  Clostridium spp. are anaerobic spore-formers.
• C. perfringens most prevalent reported form of
  food poisoning in the U.S. with 248,000 cases/yr.
• Fresh and improperly canned foods are affected,
  ex. raw honey ? infants.
• Diagnosis by demonstrating toxin in patient
  serum, or the toxin or Clostridium botulinum in
  suspected food products, or presence of the toxin
  or organism in bowel contents of infants
  (organism will colonize infants).
• Treatment involves administration of antitoxin
  and supportive therapy.

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Salmonellosis

• Salmonella colonizes intestinal epithelium and
  causes headache, chills, vomiting, diarrhea,
  fever, may result in septicemia ? typhoid fever
  (S. typhi)
• 45,000 documented cases/yr. in U.S., but probably
  lt4 of cases are reported.
• Affects fresh food, ex. eggs, meat, dairy
  products.
• Diagnosis made by observation of clinical
  symptoms, history of recent food eaten, culture
  of organism from feces. Supportive therapy for
  entercolitis, antibiotic therapy for septicemia.

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Pathogenic E. coli

• Enterohemorrhagic E. coli, ex. E. coli 0157H7,
  produce verotoxin ? bloody diarrhea, kidney
  failure.
• 60,000 infections, 50 deaths/yr., leading cause
  of kidney failure in children.
• Most common cause is undercooked meat.
• Diagnosis involves culture from the feces, ID of
  O and H Ag and toxins by serology.
• Treatment involves supportive therapy,
  antibiotics.

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Campylobacter

• Cause most prevalent bacterial foodborne
  infections in the U.S. ? high fever, headache,
  malaise, nausea, abdominal cramps, profuse
  diarrhea (watery, bloody).
• 2 million annual cases of bacterial diarrhea.
• Affects poultry (normal flora), pork, shellfish.
• Spontaneous recovery in 1 week.
• Diagnosis from presence in stool, immunological
  assays. May treat with antibiotics.

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Listeriosis

• Widely found in soil and water, no fresh food is
  safe from contamination ? can cause bacteremia,
  meningitis.
• Usually affects processed foods (meats).
• 2500 cases/yr. in U.S., 500 deaths.
• Diagnosis by culturing organism from blood or
  spinal fluid. Treat with antibiotics.

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Other Foodborne Infectious Diseases

• Bacillus cereus
• Hepatitis A
• Giardia
• Toxoplasma gondii
• Prions ? Creutzfeldt-Jakob Disease, BSE