MICROBIAL SPOILAGE OF FOOD

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”

ITS STILL GOOD TO EAT, RIGHT?

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”

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

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

CAUSES/SYMPTOMS OF MEAT SPOILAGE

Oxygen Microbial agent Symptoms

Present Aerobic bacteria

•Surface slime•Discolouration•Gas production•Change in odor•Fat decomposition

Present Yeasts•Surface slime•Discoloration•Change in odor and taste•Fat decomposition

Present Molds•Sticky and "whiskery" surface•Discoloration•Change in odor•Fat decomposition

Absent Anaerobic bacteria•Putrefaction and foul odors•Gas production•Souring

]

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

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

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

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

Year Event Agent Vehicle Company Infected Deaths Notes

2011 2011 Germany E. coli O104:H4 outbreak

E. coli O104:H4 fenugreek sprouts[4]

03950 !>3,950[5] 053 !53[6]

Deadliest bacterial foodborne outbreak in Europe. Deadliest E. Coli outbreak.

2011 2011 United States listeriosis outbreak in cantaloupes

Listeria cantaloupe[2] Jensen Farms 00146 !146 030 !30[7]

Second deadliest bacterial foodborne outbreak in US. Second deadliest Listeria outbreak.

2008 2008 Canadian listeriosis outbreak in cold cuts

Listeria cold cuts Maple Leaf Foods[8] 00050 !>50 022 !22[9]

Deadliest foodborne outbreak in Canada.

2008 2008 United States salmonellosis outbreak in peanuts

Salmonella peanuts Peanut Corporation of America

000200 !>200 009 !9

Largest foodborne salmonella outbreak in peanut butter. One of the largest food recalls in United States history.[12]

2006 2006 North American E. coli O157:H7 outbreak in spinach

E. coli O157:H7 spinach Dole Foods[13] 00205 !>205[13] 003 !3 [15]

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

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

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