Meat Products

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Meat Products
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Post-slaughter changes

• oxygen depletion
• anaerobic metabolism
• glycogen -gt glucose1P -gt 2lactate 3ATP
• ATP hydrolysis, H accumulation
• when ATP is depleted
• no energy for muscle relaxation
• actin and myosin form strong bonds
• rigor mortis stiff, inextensible muscle
• pH decreases (5.5 in beef)
• softening

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Post-slaughter changes

• stops in 1-36 h
• species (0.5 h chicken, 6-12 h beef)
• cooling rate
• stress before death
• if stressed (exercise, fasting, hot or cold T,
  fear) glycogen depletion, shorter time to reach
  rigor mortis
• toughness

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pH

• textural quality
• water holding capacity
• resistance to microbial growth

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• tenderizing
• 10-20C until pass into rigor
• refrigeration 1-2 weeks
• enzymes breakdown proteins
• low temperature cold shortening
• high temperature fast rigor mortis, fast
  shortening
• prerigor freezing (thaw rigor)

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Beef

• Cold shortening
• rapid chilling
• rapid contraction
• increased toughness
• interruption of aging
• especially in beef and lamb

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• Dark cutting
• under stress
• fast glycogen depletion
• high pH
• increased water holding
• Dark, Firm, Dry
• swollen fibers scatter less light so dark

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• Pale-soft-exudative condition
• rapid decrease in pH at high T
• denaturation of proteins
• shrunken fibers scatter more light so pale
• poor water-holding capacity
• soft texture

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Beef deterioration

• 1. Color loss
• 2. Bacterial spoilage
• psychrotrophs, slime, off-odor
• 3. Acid development, oxidation, water loss
• 4. Sensory changes (odor, flavor, texture)

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Color loss

• Myoglobin (Fe2) purplish red - low O2
• Oxymyoglobin (Fe2) bright red - 80 O2
• oxygenation
• Methmyoglobin (Fe3) brown - 0.5 O2
• oxidation
• metal ions promote autoxidation
• Nitrosomyoglobin (Fe2) bright pink

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Prevention

• 1. Color loss
• MAP, 15CO285O2
• 2. Bacterial spoilage
• good hygiene
• MAP CO2 also reduce pH
• irradiation

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Open dating

• pack date by retailer
• use by
• freeze by

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Poultry

• 1. Pathogen growth
• 2. Microbial decay
• 3. Sensory changes
• 4. Chemical and enzymatic degradation
• color, rancidity
• 5. Texture degradation
• pale, soft, exudative condition, rapid decrease
  in pH
• under stress, high T
• water loss
• crumbliness

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Flavor

• Inosinic acid (freshness index)
• inosine hypoxanthine (bitter)
• Rancidity
• high PUFA (14-23)

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Prevention

• controlled low T
• proper air circulation
• proper moisture control
• control air composition
• packaging
• polymer films
• prevent moisture loss
• vacuum packaging

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Fish

• 1. Bacterial spoilage
• TMAO in marine species (osmoregulator)
• Pseudomonas, Flavobacterium, Achromobacter
• TMAO -gt TMA (fishy odor)
• TMAO -gt DMA Formaldehyde
• Formaldehyde
• crosslink proteins
• decrease solubility, water holding capacity
• toughness
• 2. Oxidation
• high PUFA (26-48)
• cis-4-heptenal

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Prevention

• cool and keep cold, ice-water
• continuously wash with water
• prevent slime development
• vacuum packaging
• MAP
• lower pH
• canning
• salting

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Frozen meat and seafood

• 1. Protein denaturation, insolubility, toughness
  (-10C)
• 2. Lipid oxidation, off flavors
• 3. Freezer burn
• sublimation of ice
• oxidation and darkening of heme pigments
• Sell by
• Best if used by