14) Microbial Spoilage and Public Health Concerns Flashcards
spoiled food isn’t necessarily ___
unsafe
why is it important to understand the causes of microbial spoilage?
to minimize losses and provide high quality food supply w/ adequate shelf life
why do meat, poultry and seafood susceptible for microbial growth?
- they are rich in nutrients which supports growth of bacterial pathogens and microbial growth
- they are “muscle foods”
how do meat, poultry and seafood differ?
1) they have different “original” microbiotas, which leads to diff succession of microbial spoilage bacteria
2) different handling and storage requirements, which leads to diff microbial succession
compare muscle tissues of health living animals to slaughtered animals
live animals: assumed that bacteria is absent or undetectable
slaughtered animals: can have deposited bacteria or contamination from natural or external origins
describe natural and external contamination sources
natural: originating from animal
external: originating from processing equipment
the abundance of microbes on food depends on what?
1) type of animal
2) hygiene of processing facility
what is the first event in contamination?
attachment of bacterial cells to the meat surface
which bacteria is considered to be best at attaching onto meat surface?
pseudomonas
what is the best way to preserve meat?
have a clean processing facility so minimal bacteria will attach to meat surface
what are biofilms?
why is it a problem?
- major issue in food processing
- can form on almost any surface and will persist extensive cleaning for years
- once formed, bacteria in biofilms can be x10 or x100 more resistant to sanitizers
what affects microbial succession?
1) conditions of slaughter
2) decontamination
3) storage
what MOs will mostly dominate food? under what conditions?
1) Enterobactericeae in aerobic conditions
2) LAB in anaerobic vacuum packaged pdts
how do microbial interactions affect microbial succession?
how does this occur with psudomonas?
- by competing for nutrients
- producing favorable or unfavorable environments for each other
- quorum sensing
pseudomonas. ..
- inhibits Shewanella and promotes Listeria
- utilizes glucose and promotes siderophores at higher rates than Shewanella
- hydrolyses proteins and provides AAs to listeria
define spoilage
consumers rejecting a food based on undesirable sensory characteristics
spoilage results in what?
- off-flavors, off-odors, off-textures, discoloration, slime
how does proteolytic and non-proteolytic spoilage affect odors?
proteolytic: putrid odors due to breakdown of AAs
non-proteolytic spoilage: sour odors
spoilage of canned foods is usually due to what?
what does it result in?
due to improper process control
results in proliferation on mesophilic spore formers
what is the energy source of spoilage bacteria?
how is this affected by different levels of O2?
glucose
with aerobic bacteria (eg. pseudomonas): metabolizes glucose faster
with facultative anaerobes (eg. Shewanella putrefaciens): metabolizes glucose slower
thus, when O2 is present, pseudomonas predominates spoilage
after glucose, what is the next primary energy source?
lactate
after glucose and lactose, what is the next energy source?
what is the result of this?
AAs
results in proteolysis becoming more evident (seen by slime, sulfur and ammonia odors)
what is the exception with crustaceans?
- their hepatopancreas has endogenous tissue enzymes that cause rapid postmortem muscle breakdown, which is independent of microbial proteases
- reason for why lobsters, crabs and crayfish are kept alive until cooking
why is it difficult to evaluate freshness?
since the definition of spoiled depends on many factors (food, preservation interventions, geography, etc…)
what is the best way to evaluate freshness of spoiled meat? why are problems with this?
what is another method?
sensory evaluation
problems
- requires trained experts
- can be very subjective
or microbiological analysis
problems:
- very general
- destructive process
ideal spoilage indicator should…. (4)
- be absent or present in very low levels in fresh tissue
- be produced by spoilage microflora
- increase /w storage time
- correlate well with sensory analysis
what is AMR?
antimicrobial resistance
where is AMR developed? when is this a concern?
AMR (antimicrobial resistance) can be developed in foodborne pathogens, which are often found in agricultural foods
it is a concern if AMR bacteria have higher resistance to common food processing treatments
define traceability
the ability to maintain credible custody of the identification of animals and their pdts from production to retail
how is traceability different with meat from a single animal vs compound products (ground beef)
single animal: good traceability
compound pdt: more complicated. May be limited to date and place
where did the demand for meat traceability originate from?
1) the need to trace BSE positive animals
2) discovery of horse meat replacing beef in IKEA meatballs
strategy for microbial control in meats includes… (6)
- harvest or shipping animals for slaughter w/ low contamination
- reduce potential for transfer of MOs to carcasses, meat and seafood from water and the environment
- apply safe and effective decontamination interventions
- apply processes (heat, pressure, irradiation) to reduce or eliminate MOs
- avoid cross contamination at all stages
- store pdts at low temp, using packing conditions that discourage bacterial growth
the type and extent of microbial contamination on fresh red meat is determined by what?
hygiene of the animals before and during slaughter
what are common microbes on fresh red meat?
gram-ned rods and micrococci (pseudomonas, enterobacteriaceae, acinetobacter, staphylococcus, micrococcu, ocryneforms, fecal streptococci)
what is the dominating spoilage MO in aerobically stored red meat?
pseudomonas spp.
what is the dominating spoilage MO in vacuum packed red meat?
gram-pos bacteria
which leads to more signs of spoilage?
a) glucose degradation
b) amino acid degradation
AA degradation
how does stress or exercise before slaughter affect tissue composition?
decreases level of glucose in tissue, which leads to faster degradation of AAs and detection of spoilage
which spoils faster?
a) intact meats (steak)
b) comminuted meats (ground beef)
why?
comminuted meats spoil faster
b/c of
- higher levels of initial contamination
- larger surface area
- cross contamination during grinding
- release of fluids for bacterial growth media due to cells rupturing during grinding
what is the difference between MOs found in steak vs in ground meat?
steak: pseudomonas on exterior (aerobic)
ground meat: pseudomonas on exterior and LAB in interior (anaerobic)
describe the microflora of processed meats
they have lower water activity due to added salt, thus there is less spoilage by gram-neg psychrotrophic bacteria under refrigeration
what MO causes spoilage in processed meats?
lower water activity tolerating bacteria:
1) lactobacilli (anaerobic)
2) micrococci (aerobic)
describe the properties of spoilage in processed meats
develops slime, souring or greening
where is slime found on processed meats?
what is it associated with?
found on surface
associated with growth of yeast, lactobacillus, neterococcus, B. thermosphacta
what is the cause of greening with processed meat?
production of H2O2 by Lactobacillus viridescens, Streptococcus, or Leuconostoc
where is most of the microbiota associated with poultry from?
the bird’s skin and feathers
what is the MOs associated with carcasses with poultry?
gram-neg bacteria (includes enterobacteriaeceae and pseudomonas spp)
what are the main steps in poultry processing?
- stunning/ killing/ bleeding
- scalding (hot water to remove feathers and cuticle)
- picking (feathers removed which aerosolizes bacteria)
- Evisceration (removal of intestinal tract; may result in tissue rupture or damage which gives more nutrients for spoilage)
- chilling (air chilling or immersion in cold water)
how does spoilage vary between air and water chilled birds?
similar number of bacteria for both but psychotropic spoilage bacteria are reduced on water chilled birds
air chilled birds loose wt; water chilled birds gain wt
what is the most common spoilage organism at refrigeration temp?
Pseudomonas spp
compare the bacterial load of aquaculture fish to wild fish
aquaculture fish have much higher bacteria load than wild fish
b/c crowding and stress in aquaculture systems enhances spread and growth of bacteria and pathogens
what are biogenic amines? how are they produced?
what do they include?
can be produced postmortem by fish or shellfish tissue
produced from decarboxylation of specific free AAs which occurs via release of decarboxylase from MOs growing on the food pdt
includes:
histamine
cadaverine
putrescine
describe the levels of free AAs in fish muscles:
a) when alive
b) after death
when alive, fish muscle is naturally rich in free AAs
after death, free AAs increases even more
how is histamine affected by cooking? why is this important?
it is not destroyed by cooking
thus even properly cooked spoiled fish can result in poisoning
describe the action of histidine decarboxylase enzyme
what is it produced by?
converts histidine to histamine
enzyme is produced by morganella morganii, which is a symbiotic bacteria in fish
what happens if nitrite used in cold smoked fish pdts is not fresh enough
putrescine and cadaverine reacts w/ nitrite to produce carcinogens
consuming biogenic amines can cause_______
scombroid food poisonings
what is scombroid food poisoning?
what are symptoms?
how long can it last?
foodborne intoxication resulting from eating spoiled fish
flushed skin, headache, itchiness, blurred vision, cramps, diarrhea
onsets 10-60mins after eating; can last for two days
what is the cause of scombroid food poisoning?
if the fish has had inappropriate storage, resulting in microbial growth and production of biogenic amines (eg. histamine)
what are symptoms of scombroid food poisoning similar to? why?
similar to a food allergy b/c histamine is the main natural chemical responsible for allergic rxns
what can be taken to alleviate symptoms of scombroid food poisoning?
antihistamines
where are pathogenic vibrios found?
water where shrimp are raised, whether there is fecal contamination or not
how do pathogenic vibrios affect shrimp?
they can attach to and colonize the exoskeletons of shrimp
what are organisms responsible for refrigerated shrimp?
psedomonas and aeromonas
what is common in shrimp rearing environments?
coliforms and salmonella
where are vibrios (pathogenic and non-pathogenic) generally found?
in the estuarine environment where bivalves are collected and farmed
what is associated with oyster outbreaks?
oysters can concentrate native water microbiome since they are filter feeders
this is a problem b/c oysters are often consumed raw
why are muscle not recommended to be eaten raw?
b/c they concentrate bacteria
