| Fresh poultry advanced spoilage | - spoilage bacteria gradually penetrate deeper tissues of the carcass
- eventually degrade muscle tissue
- strong proteolytic activity of predominant aerobic spoilage bacteria
- strong sulfide odors, softening, exudate, discoloration, gas production |
| Reduction of microbial spoilage in raw meat | - low temps (0-1C): slows/stops microbial growth
- modified atmosphere packaging (MAP): carbon dioxide and/or nitrogen, inhibits growth of aerobes
- vacuum packaging: removal of air (21% oxygen), inhibits growth of aerobes |
| Predominant bacteria type in spoilage of refrigerated fresh meat? | Psychrotrophic bacteria |
| Microbial food spoilage: causes | - microbial growth
- release of enzymes into food |
| Microbial food spoilage: changes | color, odor (enzyme production), texture, slime formation (microbial growth), gas accumulation, and release of liquid (exudate or purge) |
| sequence of food spoilage events | - microbes enter food
- food environment favors microbial growth
- storage temp. allows growth of 1+ microbial type
- food stored long enough to allow multiplication to high numbers |
| Microbial types: significance | - bacteria, yeast, and molds ALL can spoil foods
- bacteria: most rapid food spoilage, followed by yeasts
- molds: spoil foods where bacteria/yeasts don't grow well (low pH, extreme temps), grow slower
- yeasts: grow in vacuum packaged foods |
| Vacuum packaging (molds vs. yeasts) | - reduce spoilage by molds
- yeasts are facultative anaerobes and can still grow in vacuum packaging |
| Significance of microbial numbers | - microbes must attain certain levels (spoilage detection level, SDL) in food to cause spoilage
- SDL varies with microorganism and type of food
- faster spoilage in foods with high initial microbial numbers than foods with low initial numbers at storage conditions that favor microbial growth
- bioprocessed foods contain very high #s of microbes that are desirable |
| Microbial numbers: bacteria/yeast spoilage | - bacteria and yeasts: 10^7/g, mL, cm2 of food |
| Microbial numbers: H2S/amine spoilage | - detection of off odors at lower levels, 10^7 cfu/g, mL, cm2
- ex amines: di- and tri-methyl amines |
| Microbial numbers: lactic acid spoilage | - spoilage linked to lactic acid: detection at higher levels, 10^8-10^9 cfu/g, mL, cm2 |
| Microbial numbers: slime formation | - detection at ~ 10^8 cells/g, mL, cm2 |
| Spoilage: fermented foods | occurs from growth of yeasts, molds (some molds can metabolize lactic acid), and undesirable bacteria (Alcaligenes and Pseudomonas spp.) |
| Sources of contamination in red meats | - skin and hide of animal (Staph, micrococcus, Pseudomonas, yeast, molds)
- intestinal tract
- workers' hands, tools
- equipment
- processing plant environment: aerosols, condensate, dust |
| Sources of contamination in poultry | - feet: microbes from skin, litter, and feces
- skin and feathers
- litter |
| Poultry contamination microbes | skin and feathers: Staphylococcus aureus, Acinetobacter spp, Moraxella spp, Enterobacteriaceae (10^4 - 10^6/g skin), clostridia spores on feet/feathers, micrococci, and most mesophilic flora.
litter has high microbial populations: 10^10-10^11 aerobic mesophiles/g, 10^8 psychrotrophs/g, 10^6 E. coli/g |
| Sources of contamination in fin-fish | - aquatic environment (warm v. cold water)
- water quality
- slime on fish
- skin
- gills
- intestinal tract |
| Fin-fish contamination microbes | from slime, skin gills, and intestinal tract of fisshes
- Acinetobacter, Moraxella, Pseudomonas, Shewanella putrefaciens
- Vibrio spp, Bacillu spp, Micrococcus spp, coryneforms |
| Fish catching method & contamination | - method contributes to amount and type of microbial contamination
- line caught fish: lower microbial contamination
- trawling: higher microbial contamination
- microbial types: based on water quality and microbial ecology of mud/debris on sea floor |
| Raw meat spoilage bacteria | gram -: Pseudomonas, Alcaligenes, Moraxella, Proteus, Aeromonas, Escherichia, Serratia
gram +: Brochothrix, Micrococcus, Lactobacillus, Enterobacter, Carnobacterium
yeasts and molds |
| What determines predominant spoilage flora? | availability of nutrients, oxygen, storage temp, storage time, pH of the meat, growth rate of the spoilage microbes |
| Predominant bacteria type in spoilage of refrigerated fresh meat? | Psychrotrophic bacteria |
| Spoilage in aerobic storage | Pseudomonas spp. will cause changes in odor, color, texture, and sliminess
aerobic bacteria grow more rapidly as more ATP generated from aerobic respiration |
| Spoilage in vacuum-packaged meat | lactic acid bacteria will predominate --> sour odor, gas, color defects |
| Reduction of microbial spoilage in raw red meat | - low temps (0-1C): slows/stops microbial growth
- modified atmosphere packaging (MAP): carbon dioxide and/or nitrogen, inhibits growth of aerobes
- vacuum packaging: removal of air (21% oxygen), inhibits growth of aerobes |
| Vacuum packaging: what is it | - meat placed in plastic bag
- vacuum packaging machine pulls out the air
- bag heat sealed to close opening
- can increase the shelf-life of meats |
| Vacuum packaging: microflora impact | - depletion of oxygen --> residual oxygen used up by aerobic bacteria and meat mitochondria (takes 1-2 days)
- growth of aerobic spoilage microorganisms inhibited when oxygen is depleted
- growth of anaerobes and facultative anaerobes increases --> shift in microflora |
| Microbial spoilage of fresh poultry: species | - low temperature spoilage by psychotropic microorgansims
- spoilage is a surface phenomenon
- typically Pseudomonas spp., Acinetobacter spp, Flavobacterium sp
- produce sulfide-like odors: methyl sulfide, dimethyl sulfide
- fungi important when antibiotics used to inhibit bacterial growth |
| Fresh poultry spoilage: sliminess | - bacterial growth and production of extracellular polysaccharides
- bacterial colonies merge to form a slime layer on surface of poultry meat or skin |
| Visceral taint | - off odor in the visceral cavity of poultry
- action of intestinal microflora |
| "New York-dressed" poultry | - birds are de-feathered but head, feet, and viscera remain intact
- birds are hung to age and develop flavor
- can be dipped in antibiotics to kill bacteria, allows molds to grow |
| Fresh poultry: detection levels | generally off-odors are detected before slime
- 10^7 CFU/cm2: off odors
- 10^8 CFU/cm2: slime
- 10^9.5 CFU/cm2: very slimy surface |
| Poultry spoilage testing | - carcasses fluoresce under UV light with high populations of fluorescent Pseudomonas spp
- carcass sprayed with tetrazolium (TTC): red pigment in areas of very high microbial activity
- typical areas for microbes: feather follicles, bruised/damaged areas |
| Fresh poultry advanced spoilage | - spoilage bacteria gradually penetrate deeper tissues of the carcass
- eventually degrade muscle tissue
- strong proteolytic activity of predominant aerobic spoilage bacteria
- strong sulfide odors, softening, exudate, discoloration, gas production |
