Food Preservation and Foodborne Microbial Diseases

1. Chapter 29 Food Preservation and Foodborne Microbial Diseases

2. 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.

3. 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.

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

5. 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.

6. 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.

7. 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 100�C, whereas nonacidic foods should be heated to 121�C. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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 <4% 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.

13. Pathogenic E. coli Enterohemorrhagic E. coli, ex. E. coli 0157:H7, 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.

14. 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.

15. 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.

16. Other Foodborne Infectious Diseases Bacillus cereus Hepatitis A Giardia Toxoplasma gondii Prions ? Creutzfeldt-Jakob Disease, BSE