microbial spoilage and public health concerns Flashcards
why is it important to understand microbial food spoilage?
to minimize economic losses and provide a high-quality food supply with adequate shelf-life
what do meat, poultry, and seafood have in common?
they are muscle foods, rich in nutrients (bacterial substrates), which allows extensive microbial growth and support the growth of bacterial pathogens
what are the differences between meat, poultry, and seafood?
They have different “original” microbiota leading to a different succession of microbial spoilage bacteria. they also differ in the handling and storage requirements, which also leads to a different microbial succession. they also differ in handling and storage requirements which also leads to a different microbial succession
under what conditions does contamination originate?
- natural: originating from the animal (GI tract, skin, feathers)
- originating from the processing environment
what is the first event in contamination?
attachment of bacterial cells to the meat surface
what bacteria is exceptionally good at attaching to meat surfaces?
pseudomonas
what is the best way to preserve meat?
having a very clean processing facility so that minimal numbers of bacteria attach to the surface of the meat
what is the significance of biofilms?
they are a major issue in food processing environments. they can form on almost any surface and can persist despite despite extensive cleaning efforts for years. once formed, bacteria can be 10- to 100- fold more resistant to sanitizers in comparison to planktonic cells
____ of all meat and __ of all fish are lost due to microbial spoilage
one fourth
30%
what conditions affect the microbial succession in meat and fish?
conditions of slaughter, decontamination, and storage
In general, _____ bacteria, mostly ______ will dominate the microflora under cold aerobic conditions, and LAB will dominate vacuum-packaged products
gram-negative
enterbacteriaceae
Pseudomonas inhibits ____and promotes ______
Shewanella
Listeria
Pseudomonas utilizes glucose and produces ____ at higher rates than Shewanella
siderophores
Pseudomonas also hydrolyses proteins and provides ____ to _____
amino acids
Listeria
what is the definition of spoilage?
consumers rejecting a food based on undesirable sensory characteristics. the definition is based on the consumer and will differ based on socio-economic factors
what does proteolytic spoilage result in?
putrid odors due to breakdown of amino acids
what does non-proteolytic spoilage result in?
sour odors
what is spoilage of canned foods due to?
improper process control, resulting in proliferation on mesophilic spore formers
what is the energy source of spoilage bacteria?
glucose
glucose is more rapidly metabolized by ____ bacteria than by ____ anaerobes
aerobic
facultative
If oxygen is present, ____ predominate in spoilage
Pseudomonas
what is the primary energy source of spoilage after glucose?
lactate, in both aerobic and anaerobic bacteria
what is the energy source after glucose and lactate?
amino acids
why are crustaceans like lobster and crayfish, kept alive until cooking?
their endogenous tissues enzymes in their hepatopancreas cause rapid postmortem muscle breakdown, independent of microbial processes
what is the best type of evaluation for quality evaluation?
sensory evaluation
the ideal spoilage indicator should…
- be absent or present in very low levels in fresh tissue
- be produced by the spoilage microflora
- increase with storage time
- correlate well with sensory analysis
What is meat traceability?
the ability to maintain credible custody of the identification of animals and their products from production to retail
the strategy for microbial control in meats is generally focused on _____ and _____
good hygiene
proper storage
methods for microbial control:
- harvest, or ship animals for slaughter with low contamination
- reduce the potential for transfer of microorganisms to carcasses, meat, and seafood from water and the environment
- apply safe and effective decontamination interventions
- apply processes such as heat, high pressure, irradiation, to reduce or eliminate microorganisms
- avoid cross-contamination
- store products at low temperature
how is the type and extent of microbial contamination determined on red meats?
determined by the hygiene of the animals before and during slaughter
common microbes on fresh red meat are ____ rods and _____
gram-negative rods
micrococci
examples of gram-negative rods and micrococci
Pseudomonas, enterobacteriaceae, acinetobacter, staphylococcus, micrococcus, coryneforms, and fecal streptococci
what bacteria are present in lower populations on red meat?
LAB, bacillus, and clostridium spores
what species of microorganisms are the dominating spoilage microorganisms in red meat?
pseudomonas spp.
what happens when meat is immediately vacuum-packed?
gram-positive bacteria will dominate the population
Remember, microbes like to use ____ before ____ for energy production, and amino acid degradation leads to more signs of spoilage
glucose
amino acids
what pre-slaughter factor leads to faster degradation of amino acids in red meat?
the animal being stressed or exercised before slaughter.
____ meats spoil more slowly than _____ meats because of higher initial contamination, larger surface, area, cross-contamination during grinding, and the release of fluids for bacterial growth media due to cells rupturing during grinding.
intact meats (steak) comminuted meats (ground beef)
processed meats have lower ___ due to added salt
water activity
spoilage by what kind of bacteria is limited in processed meats?
gram-negative psychotropic bacteria
spoilage by what kind of bacteria is prevalent in processed meats?
lactobacilli (anaerobic) or micrococci (aerobic)
examples of processed meats:
- bologna
- cooked or fermented sausage
- cold-cuts
sliming is the result of what bacteria?
growth of yeasts, lactobacillus, enterococcus, and B. thermosphacta
greening is the result of waht bacteria?
production of hydrogen peroxide by lactobacillus viridescens, streptococcus, or leuconostoc
how do dry-cured meats spoil?
presence of yeasts or molds that tolerate extremely low water content
most of the microbiota associated with poultry is acquired from which regions of the bird?
bird’s skin, feathers
bacterial populations associated with the carcass at the end of processing are _____ bacteria
predominantly gram-negative
gram-negative bacteria in carcasses at the end of processing?
Acientobacter/ morazella, enterobacteriaceae, and pseudomonas
during refrigeration storage, ____ spp. group becomes predominant
pseudomonas
steps of processing poultry:
- stunning/ killing / bleeding
- Scalding
- picking
- evisceration
- chilling
stunning/killing
Birds are placed onto moving shackles and are stunned with electricity or low oxygen
scalding
birds are immersed in hot water to ease the removal of feathers
picking
the feathers are removed by placing the bird in a picker, containing rubber fingers to grab the feathers and full them out. this process aerosolized bacteria and can spread them to other carcasses
evisceration
Intestinal tract is mechanically removed. this could sometimes damage thigh and back muscles resulting in tissue rupture and more nutrients being available for spoilage. intestines could also rupture leading to fluid leakage into the carcass which increases bacterial load
chilling
carcasses chilled to reduce microbial growth which improves shelf-life and food safety. air chilling is the most common method
spoilage bacteria metabolizes _____ first, which leads to a CFU population of _____
glucose
10^8 CFU/cm^2
the most common spoilage organism at refrigeration temperatures is ______ but ____ can also be involved in spoilage
Pseudomonas spp.
yeasts
what are foodborne pathogens associated with seafood?
salmonella, Clostridium botulinum, aeromonas, S. aureus, L. monocytogenes, vibrio cholerae, vibrio parahaemolyticus, and vibrio vulnificus
aqua-cultured fish tend to have a higher ______ than their wild counterparts
bacterial load
What are biogenic diamines?
compounds produced by decarboxylation of specific free amino acids, which are produced by postmortem fish or shellfish tissue
how does decarboxylation occur?
via the release of decarboxylase from the various microorganisms growing on the food product
fish muscle is naturally rich in free ____, and this increases even more after the fish dies
amino acids
What are some biogenic diamines?
histamine, cadaverine, and putrescine
_____ is not destroyed by cooking, so even properly cooked spoiled fish can result in poisoning
histamine
what is a consequence of nitrite being used in cold-smoked fish products that aren’t fresh enough?
putrescine and cadaverine will react with nitrite, producing carcinogens
consuming biogenic amines can cause what type of food poisoning?
scomboid food poisonings (a disease due to the ingestion of contaminated food, mainly in fish)
symptoms of scombroid food poisoning?
flushed skin, headache, itchiness, blurred vision, abdominal cramps, and diarrhea
how long can scombroid food poisoning last?
2 days
how fast do scombroid food poisoning symptoms come on?
10-60 minutes after eating
what are the causes of scombroid food poisoning?
fish being improperly stored, which results in microbial growth, resulting in the production of biogenic amines, such as histamine
_____ is the main natural chemical responsible for true allergic reactions, so the symptoms are almost identical to a food allergy
Histamine
what can be taken to alleviate symptoms of scombroid food poisoning?
anti-histamines
____ are the most exportable seafood product in the world
Shrimp
what are pathogenic vibrios?
gram-negative bacteria that cause illness
____ can attach to and colonize the exoskeletons of shrimp
pathogenic vibrios
what organisms are responsible for refrigerated shrimp spoilage?
pseudomonas and aeromonas
what kind of contamination of growing ponds where shrimp are produced, is most common?
fecal contamination, coliforms, and salmonella are common in shrimp rearing environments
____ are filter feeders that can concentrate the native water microbiome
Oysters
why is it that consuming oysters raw, is problematic?
eating raw oysters is associated with several outbreaks
what other type of shellfish besides oysters, is also problematic to eat raw?
mussels - concentrate bacteria
