Microbial Spoilage of Food

1. Microbial Spoilage of Food

2. Microbial Spoilage of food • A food product is defined as “spoiled” if “sensory changes make it unacceptable to the consumer” • Indications of spoilage include: development of “off-flavors,” odors, slime/biofilm, color change, bad taste, or any other characteristic that is undesirable to the consumer • Spoilage is usually caused by the decomposition and formation of metabolites resulting from microbial growth • Food capable of spoiling is referred to as “perishable food”

3. Its still good to eat, right?

4. Why do foods spoil? • Foods decompose from the moment they are harvested due to attacks from enzymes, oxidation and microorganisms. These include bacteria, mold, and yeast. • As microbes enzymatically digest the food and use it for themselves, they produce metabolic by products – some of these may be health hazards • Spoilage microbes do not have to be pathogenic – they usually just produce toxic waste • Spoilage may be harmless or slightly detract from quality; some spoiled foods may be harmful to consume • Uncooked or under-cooked animal flesh that is allowed to spoil is typically very toxic • The toxic effects from consuming spoiled food are referred to as "food poisoning", and more properly as "foodborne illness”

5. Preventing spoilage • Preservatives- naturally occurring or synthetically produced substance used to expand the shelf life of food; lengthens the time it can be harvested, processed, sold, and kept in the consumer's home • Refrigeration– increases the shelf life of certain foods/beverages; Freezing can preserve food even longer - both have limitations

6. Spoilage in Red meat • Levels of bacteria in healthy, live animals is extremely low • Levels of bacteria are high in the hair, hide, hooves, and intestinal tracts of red-meat producing livestock • Contamination of meat often occurs during skinning, hair-removal, or if the abdominal cavity is punctured • Contamination during handling and post-processing may also introduce microbes

7. ] Causes/Symptoms of meat spoilage

8. Spoilage in poultry • Skin, feathers, feet, intestines, litter and feces of poultry harbor many potential microbial contaminants • Transportation of birds and processing in slaughter houses are commonly associated with spread of microbes

9. Spoilage in fish • Microbial contaminants in fish are strongly influenced by their collection environments, season, temperature, handling and processing • Water temperature is especially influential > warm water = more microbes • Trawled (dragging with nets) fish usually have more microbes than those fished from lines – debris from seafloor, compaction of fish in nets

10. Canning • Canning of food - preserves food for longer periods of time, whether canned at home or commercially • Canned food is vacuum packed in order to keep oxygen out of the can that is needed to allow bacteria to break it down • Canning does have limitations, and does not preserve the food indefinitely

11. Preservation of food • Lactic acid fermentation also preserves food and prevents spoilage through competitive exclusion, by raising pH and preventing exposure to other sources of nutritional degradation, such as oxidation, heat and sunlight • Dried foods can last a long time, sometimes nearly indefinitely • Pasteurization – preserves liquid food; prominently applied to milk - milk is heated at about 70°C for 15 to 30 seconds to kill the bacteria present in it and cooling it quickly to 10°C to prevent the remaining bacteria from growing; it is then stored in sterilized bottles or pouches in cold temps • Meats may be smoked for preservation – best if combined with salt curing or drying

13. Food spoilage pathogens: Listeria • Listeria common in the environment; rarely causes infections in people • About 1,600 people in the United States get sick from Listeria each year; rapid treatment with antibiotics is usually successful • Mostly effects pregnant women and their babies, people with weakened immune systems, and people 65 years or older - at least 90 percent of reported Listeria infections • Listeria may survive being frozen; it spreads through the bloodstream to cause meningitis - often fatal • Processed deli meats, poorly washed vegetables/fruits and unpasteurized milk are common sources

14. Food Spoilage Microbes: Salmonella • Salmonella - mobile, non-spore forming, facultative anaerobe bacteria • Typically present in human and animal intestines; infections that spread beyond intestines may be severe • Most frequently spread by direct fecal-contaminated water or food; sensitive to gastric acid in the stomach – high amounts must be ingested • Most healthy people recover within a few days without specific treatment • May survive for weeks outside a living body; not destroyed by freezing;perish after being heated at least ten minutes at 75 °C (167 °F) – must be inner temp of food • Symptoms: diarrhea, fever, vomiting, and abdominal cramps 12 to 72 hours after infection. In most cases, the illness lasts four to seven days, and most people recover without treatment • ~ 40,000 cases of Salmonella infection are reported each year in the USA

15. Spoilage of Dairy Products • Good growth medium b/c high water content, many available nutrients, near-neutral pH, but milk fat is difficult for most microbes to access and many microbes cannot utilize lactose. Freshly collected raw milk contains many natural microbial growth inhibitors • Lactoperoxidase system of fresh, raw cow milk inhibits LAB, coliforms, and many pathogens • Pasteurization partially destroys lactoperoxidase inhibitory system • Yogurt is acidified milk – lower pH; cheeses are lower pH than yogurt and have higher salt and less water (lower spoilage potential) • Butter is a water-oil emulsion – most microbial growth is inhibited in salted butter; unsalted butter relies on low pH and refrigeration for preservation