Transcript Spoilage organisms

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, hairremoval, or if the abdominal
cavity is punctured
• Contamination during
handling and post-processing
may also introduce microbes
]
CAUSES/SYMPTOMS OF MEAT
SPOILAGE
Oxygen
Present
Present
Present
Absent
Microbial agent
Symptoms
Aerobic bacteria
•Surface slime
•Discolouration
•Gas production
•Change in odor
•Fat decomposition
Yeasts
•Surface slime
•Discoloration
•Change in odor and taste
•Fat decomposition
Molds
•Sticky and "whiskery" surface
•Discoloration
•Change in odor
•Fat decomposition
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
2011
2011 Germany E.
coli O104:H4
outbreak
E. coli O104:H4
fenugreek
sprouts[4]
2011
2011 United States
listeriosis outbreak Listeria
in cantaloupes
2008
2008 Canadian
listeriosis outbreak Listeria
in cold cuts
cantaloupe[2]
cold cuts
Company
Jensen Farms
Maple Leaf
Foods[8]
Infected
Deaths
03950 !>3,950[5]
053 !53[6]
00146 !146
00050 !>50
Notes
Deadliest
bacterial
foodborne
outbreak in
Europe. Deadliest
E. Coli outbreak.
030 !30[7]
Second deadliest
bacterial
foodborne
outbreak in US.
Second deadliest
Listeria outbreak.
022 !22[9]
Deadliest
foodborne
outbreak in
Canada.
2008
2008 United States
salmonellosis
Salmonella
outbreak in
peanuts
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
E. coli O157:H7
O157:H7 outbreak
in spinach
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