Microbiological Spoilage Flashcards
How are meat, poultry similar and how do they differ?
they are msucle foods, they are rich in nutrients (aka bacterial substrates) which allow for extensive microbial growth and support the growth of bacterial pathogens. They differ in that they have differet original microbiotas, leading to a different succession of microbial spoilage bacteria. They differ in the handling and storage requirement, which also leads to a different microbial sucession.
it is generally accepted that bacteria are ________________ in very ___ number within muscle tissues of healthy, live animals
absent, undetectable or present in very low
what processes deposit bacteria on the exposed surfaces of adipose or muscle tissue?
slaughtering, dressing or catching
how can contamination originate in meats?
natural; from the animal ie GI or feather
external; processing environment
what is the first event in contamination in meat? what is the best bacteria for this
attachment of bacterial cells to the meat surface. Pseudomonas.
what is a major issue in food processing environments? why?
biofilms. They can form on almost any surface and can persist despite extensive cleaning efforts for years.
biofilms are resistant to sanitizers in comparison to planktonic cells.
In general _____ will dominate microflora under cold aerobic conditions and LAB will dominate vaccuum packaged products
aerobic gram negative enterobacteriaceae
what is spoilage/types of spoilage.
Spoilage is defined by consumers rejecting a food based on undesirable sensory characteristics
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
Explain the energy sources of spoilage bacteria
- energy source = glucose
- glucose is more rapidly metabolized by aerobic bacteria (pseudomonas) than by facultative anaerobes there is o2 = present pseudomonas predominate.
- after glucose = lactate is primary energy in both aerobic and anaerobic conditions.
- after = amino acids as energy source.
explain the interactions between microbes in food spoilage of meets
microbes compete for nutrients produce favorable or unfavorable environments for eachother 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
what is the best way to evaluate freshness of spoiled meat?
sensory evaluation and microbiological analysis.
quantitative biochemical changes to define spoilage level like production of amines, ammonia, trimethylamine, sulfur etc.
The ideal spoilage indicator should be
- absent or present in very low levels in fresh tissue
- be produced by spoilage microflora
- increase with storage time
- correlate well with sensory analysis.
what is traceability and why is it considered important with respect to food spoilage?
It is the ability to maintain credible custody of the identification of animals and their products from production in retail.
essential for protection of human and animal health.
What are strategies used to establish microbial control in meat?
The strategy for microbial control in meats is generally focused on good hygiene and proper storage and includes:
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 stages
Store products at low temperature, using packing conditions that discourage bacterial growth (we will talk more about storage later on)
Explain microbial contamination in red meats?
- determine before and during slaughter
- initial contamination levels = aerobic mesophiles
- common microbes = gram negative rodes and cocci. Pseudomonass, staphylococcus.
lower pop = LAB bacillus and Clostridium spores
what is the difference between aerobically stored and vacuum packed meats?
aerobically, cold= psuedomonas
vacuum packed = gram positive bacteria.
what is the effect of a stressed or exersized animal before slaughter?
decreased levels of glucose in the tissue so it leads to faster spoilage.
T or F: steak spoils faster than ground beef
F; higher levels of initial contamination, larger surface area, cross contamination during grinding, release of fluids for bacterial growth media during grinding
what is the dominant microflora in ground meat exterior and interior?
exterior = pseudomonas interior = LAB due to oxygen limitation
Explain the causes of spoilage of processed meats
Processed meats have lower water activity, due to added salt, than fresh meats and therefore, spoilage by Gram-negative psychrotrophic bacteria under refrigeration is limited
Instead, processed meats are spoiled by lower-water-activity tolerating bacteria such as lactobacilli (anaerobic) or micrococci (aerobic)
Processed meats such as bologna, cooked or fermented sausage, or cold-cuts spoil in a different way and usually develop slime, souring, or greening
Slime is usually confined to the surface and is associated with the growth of yeasts, Lactobacillus, Enterococcus, and B. thermosphacta
Greening is due to the production of hydrogen peroxide by Lactobacillus viridescens, Streptococcus, or Leuconostoc
Dry-cured meats mostly spoil because of yeasts or molds that tolerate extremely low water content
processed meats are mainly spoiled by
lower water acitivity tolerating bacteria like Lactobacilli or microcci
dry and cured meats mostly spoil because of yeast and molds that can tolerate low water content.
