Basic Science of Meat Processing

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Basic Science of Meat Processing

• Lynn Knipe
• Associate Professor
• Animal Science

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Rigor Mortis

• stiffness of death
• convert muscle to meat
• muscles contract with no relaxation
• delay of onset time for prerigor (hot)
  boning/salting

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Delay of onset of rigor mortis
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Rigor Mortis

• drop in pH from 7.0 to 5.6
• deviations in pH drop
• Pale, Soft and Exudative (PSE) pork
• Dark, Firm Dry (DFD)

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Factors affecting postmortem changes in pork
quality

• Stress
• 1 genetic susceptibility
• Porcine Stress Syndrome (PSS)
• fiber types

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Factors affecting postmortem changes in pork
quality

• Stress
• 18 due to handling
• timing of stress pH
• chill to lt68F (gt50F) - 4 hrs
• low pH and high temperature
• pale, soft exudative (PSE)
• carriers?

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Blue dots between actin and myosin, represent
water molecules.
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PSE Ham
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Combo bin of boned hams, showing PSE areas in
center of ham, around femur bone.
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PSE Pork Loin
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Chops gas-flushed with CO2, PSE chop in center.
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Top muscle rapidly chilled, Bottom muscle, slowly
chilled (Paired Inside Ham Muscles)
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Factors affecting postmortem changes in pork
quality

• Stress
• 35 dark, firm dry (DFD)
• pale vs. soft and exudative

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Factors affecting postmortem changes in pork
quality

• Stress
• Stunning method
• CO2/electrical

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Other Pork Quality Types

• Red, Firm and Non- exudative (RFN)
• Red, Soft Exudative (RSE)
• Pale, Firm and Non- Exudative (PFN)
• Hampshire Effect

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Fiber Types

• Red fiber types
• slow contraction, no rest
• smaller diameter fibers
• e.g., heart, long distance runners dark
  meat of poultry

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Fiber Types

• White fiber types
• rapid contraction, with rest
• anaerobic met. - lactic acid
• larger diameter fibers
• muscles of hogs and sprinters

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Properties of Fresh Meat

• Water-holding capacity (WHC)
• ability to retain water during cutting,
  grinding, cooking, pressing, drying,
  chewing, etc.

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Postmortem effects on WHC

• Net charge effect
• repulsion/attraction of magnetic poles
• iso-electric point
• pH 5.15.3
• actomyosin formation

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Effect of pH on Water-Holding Capacity of Meat
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Postmortem effects on WHC

• denaturation PSE

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Processing Effects on WHC

• Salt
• increases WHC
• shifts isoelectric point to lower pH

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Processing Effects on WHC

• Phosphates
• raise pH
• increase net charges
• chelate Fe, Mg, etc.
• specific protein effect
• pyrophosphates

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Processing Effects on WHC

• freezing and thawing
• cell wall disruption
• fermentation
• reduced pH, reduces WHC

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Frozen meat quality affected by

• Freezing method
• meat freezes 26.528F
• slow increase crystal size and damage
• darkens color
• dehydration

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Freezing vs. Thawing Rate
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Cross-section of muscle fiber, showing moisture
(blue) in intracellular and extracellular spaces.
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Cross-section of frozen muscle fibers, with small
ice crystals.
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Slow freezing causes purer extracellular moisture
to freeze first, resulting in large, damaging ice
crystals.
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Frozen meat quality

• Storage conditions (1)
• low/uniform temperatures
• 0 to -22F (slows crystals)
• lt14F stops most bacterial and enzyme activity
• need vapor/gas barriers

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Freezer storage time is often abused.
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Frozen meat quality

• Thawing methods
• slowly at refrigd temps
• lt70F water
• microwave tempering for product to be ground
• thaw rate size of product thermal capacity-
  fat vs lean

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Frozen meat quality

• Condition of meat when frozen
• rancidity bacteria
• Refreezing

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Three questions to ask related to frozen meat

• How was it frozen?
• When was it frozen?
• Why was it frozen?

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Length of storage

• gradual loss of WHC over time

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