Microbial spoilage Flashcards
Why it is necessary to understand microbial food spoilage mechanism?
- A spoiled food isn’t necessarily unsafe
- Spoiled food is mostly an economic issue, but it’s also a food security issue
- Therefore, understanding the causes and mechanisms of microbial spoilage is important in order to minimize the losses and provide a high-quality food supply with adequate shelf life
What is common and different between meat, poultry, and seafood?
- These products are all similar in that they are “muscle foods”
- They are rich in nutrients (aka bacterial substrates), which allows extensive microbial growth and support the growth of bacterial pathogens and high in moisture
- They differ in that they have different ”original” microbiotas, leading to a different succession of microbial spoilage bacteria
- They differ in the handling and storage requirements, which also leads to a different microbial succession
Is meat free from bacteria when alive? when it can be acquired? Sources
What is the first event in microbial meat contamination and who is good at it?
, the best way to preserve meat is …
- In general, the best way to preserve meat is to have a very clean processing facility so that minimal numbers of bacteria attach to the surface of the meat
- Animal carcasses must also be washed with potable water immediately after slaughter in North America
What is the measure threat for food processing environments?
Biofilms
- They can form on almost any surface (stainless steel, aluminum, nylon, Teflon, rubber, plastic, gaskets etc.) and can persist despite extensive cleaning efforts for years!?!
- Mono- or multispecies bacteria can be formed by spoilage or pathogenic bacteria
- Once formed bacteria in biofilms can be 10- to 100-fold more resistant to sanitizers in comparison to planktonic cells
What bacteria is very good at colonizing stainless steel?
Lysteria monocytogenes
How much of meat and fish is wasted at all stages and why it is a problem
•One-fourth of all meat, and 30% of all fish are lost due to microbial spoilage!!!
Terrible-> people could have eaten
2-> Carbon emissions
3-> animal welfare
What affects microbial succession patterns and general rules?
- Conditions of the slaughter, decontamination, and storage will affect the microbial succession
- But in general aerobic Gram-negative bacteria mostly Enterobacteriaceae will dominate the microflora under cold aerobic conditions, and LAB will dominate vacuum-packaged products
How microbial interaction play a role in microbial succession and give a concrete example
- Microbial interactions also play a role, microbes compete for nutrients, produce favorable or unfavorable environments for each other, and quorum sensing and this can also affect microbial succession
- Pseudomonas inhibits Shewanella and promotes Listeria
- Pseudomonas utilizes glucose and produces siderophores at higher rates than Shewanella
- Pseudomonas also hydrolyses proteins and provides amino acids to Listeria
Why spoilage is not a set term?
- Spoilage is defined by consumers rejecting a food based on undesirable sensory characteristics
- Based on the definition of spoilage it is at the discretion of the consumer (subjective), and will differ based on socio-economic factors
What will be the difference in proteolytic, non-proteolytic and canned food spoilage
- Microbial spoilage can lead to off-flavors, off-odors, off-textures, discoloration, and slime
- Proteolytic spoilage results in putrid odors due to breakdown of amino acids
- Non-proteolytic spoilage results in sour odors
- Spoilage of canned foods is usually due to improper process control, and results in the proliferation on mesophilic spore formers
What are the substrates, chemical changes, and spoilage happening in meat (both aerobic and anaerobic)
why lobsters, carbs, and crayfish are kept alive until cooking
•Crustaceans are an exception to the rules above because endogenous tissue enzymes in their hepatopancreas cause rapid postmortem muscle breakdown, this is independent of microbial proteases
What is the ideal spoilage indicator should have
- 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
Is it easy to evaluate the spoilage of the meat?
- The definition of Spoiled will depend on the food, preservation interventions, geography, so its hard to come up with a really good way to evaluate freshness
- Sensory evaluation is probably the best way to evaluate freshness of spoiled meat, but this requires trained experts for regulatory purposes and is very subjective
- Microbiological analysis is also available, but its very general and can be a destructive process
- Efforts have been made to develop quantitative biochemical changes to define spoilage level (production of amines, ammonia, trimethylamine, and sulfur)
What is traceability?
•Traceability is the ability to maintain credible custody of the identification of animals and their products from production to retail
Why traceability is important?
•The strategy for microbial control in meats is generally focused on good hygiene and proper storage and includes:
- Select
- Reduce
- Decontaminate
- Process
- No cross-contamination
- Low T storage
- 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 (heat, high pressure, irradiation) to reduce or eliminate microorganisms
- Avoid cross contamination at all stages6.Store products at low temperature, using packing conditions that discourage bacterial growth (we will talk more about storage later on)
Common microbes on fresh red meat are ___
Present in lower populations ___
•Gram-negative rods and micrococci (Pseudomonas, Enterobacteriaceae, Acinetobacter, Staphylococcus, Micrococcus, coryneforms, and fecal streptococci)
LAB, Bacillus, and Clostridium spores
What is the range of microbes on meats?
•Initial contamination levels vary from 102-107 CFU/cm2of aerobic mesophiles
___ are the dominating spoilage microorganisms in red meat at cold temperatures, on aerobically stored meat
•Pseudomonas spp.
What is dominant bacteria whem the meat is immediately vacuum packed?
Gram-positive bacteria
Why stressed animal’s meat will become spoiled more quickly?
Remember microbes like to use glucose before amino acids for energy production, and amino acid degradation leads to more signs of spoilage
•If the animal was stressed or exercised before slaughter it will lead to decreased levels of glucose in the tissue, this leads to faster degradation of the amino acids and detection of spoilage at lower bacterial cell densities (106CFU)
How microflora and spoilage is different in stakes vs ground beef?
- Intact meats (steak) spoil more slowly than comminuted meats (ground beef) because of higher levels of initial contamination, larger surface area, cross contamination during grinding, the release of fluids for bacterial growth media due to cells rupturing during grinding
- In ground meat the dominant microflora on the exterior are similar to steak (Pseudomonas) but LAB may dominate the interior due to oxygen limitation
How processed meats degradation is different from fresh?
The greening of the surface for processed meats is due to what type of bacteria?
•Greening is due to the production of hydrogen peroxide by Lactobacillus viridescens,Streptococcus, or Leuconostoc
Slime in processed meats is due to what bacteria?
•Slime is usually confined to the surface and is associated with the growth of yeasts, Lactobacillus,Enterococcus, and B. thermosphacta
What spoils dry-cured meats?
•Dry-cured meats mostly spoil because of yeasts or molds that tolerate extremely low water content
How much poultry is consumed globally?
•Approximately 31% of meat consumed globally is poultry, most of this is chicken
Where chicken get its bacteria? and how much
- Most of the microbiota associated with poultry is acquired from the bird’s skin and feathers, with some acquired during processing
- At the end of processing most poultry products have a bacterial population ranging from 101-104 CFU/cm2
- Each step in the processing of raw poultry will affect the level and type of spoilage bacteria, with some steps leading to an increase in population and some steps leading to a decrease
Specific types of bacteria that are found on poultry
- Bacterial populations associated with the carcass at the end of processing have predominantly Gram-negative bacteria (Acientobacter/ Morazella, Enterobacteriaceae, and Pseudomonas spp.)
- During refrigeration storage the Pseudomonas spp. group becomes predominant
What is the processing poultry from live chicken to end product? what are the specifics of each step?
What is the last step of poultry processing after evisceration? How it can be achieved? what is lost during this period, do not forget about bacteria
What substrate is first used when chicken is spoiled And then what? the most common spoilage organism at refrigeration temperature?
- Again, the spoilage bacteria metabolize glucose first, which leads to a population of 108 CFU/cm2
- After glucose is used, the bacteria metabolize amino acids which leads to the production of off-odors
- The most common spoilage organism at refrigeration temperatures is Pseudomonas spp. but yeasts can also be involved in spoilage
Several foodborne pathogens are associated with seafood including
•Salmonella, Clostridium botulinum, Aeromonas, S. aureus, L. monocytogenes, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus
Where most fish is coming from nowadays and what is the implication?
•For several years wild fisheries supplied the world with fish, now aquaculture has outpaced wild fisheries, therefore the species variety is more limited
The crowding and stress found in aquaculture systems enhance the spread and growth of bacteria (especially pathogens) so aquacultured fish tend to have a higher bacterial load than their wild counterparts