Meat science

• Homeostasis - Maintenance of a physiologically balanced internal environment (Premortem condition)


  • Blood pressure
  • Oxygen concentration
  • Energy supply
  • Temperature
  • pH
• What happens postmortem


  1. Blood is removed from the body - O2 depletion

  2. Without oxygen, cells use anaerobic metabolism

  3. Lactic acid starts to build up and blood is no longer removing waste products

  4. Blood was also cooling the body heat produced by active metabolism
• Glycogen


  A major energy source in muscle
• Glucose


  Delivered by the blood and stored as glycogen in muscle
• Glycolysis


  Breakdown of glucose/glycogen for release of energy which produces pyruvate or lactic acid
• Muscle Metabolism


  When the muscle stops receiving blood, oxygen is no longer present, and anaerobic metabolism begins
• Acid Build-Up


  Pyruvate → Lactic Acid = Lower pH
• pH


  Inverse log of H+ ions, substances with high amounts of H+ will have a low pH

  pH = -log [H+] = log 1/[H+]
• Factors influencing pH drop

  • Genetics/Muscle fiber type
  • Stress - body temperature, respiration, blood pressure alters during stressful situations
  • Amount of glycogen present
  • Postmortem temperature - cooling rate
• PSE: Pale, Soft, Exudative (Hereditary)


  • High Stress animals experience short term glycogen depletion prior to death. Due to excitement or holding on a kill floor for longer time. Most commonly occurs in Swine and Turkey, especially those genetically prone to stress. In Turkey, Ryanodine receptor defects in the calcium channel
• Pig Genotypes


  • Halothane (Hal -1843) mutation: Porcine Stress Syndrome (PSS) - calcium-release channel defect in sarcoplasmic reticulum (SR), body temperature, rapid pH decline
  • Rendement Napole (RN-): Hampshire Effect - mutation in AMP-activated protein kinase, muscle glycogen storage, ultimate pH
• PSE Meat


  • Glycogen is used up during stress, lactic acid builds up with negative effects on palatability
  • Low pH
  • Low water holding capacity (WHC)
  • Less valuable in processing due to lower WHC
  • Reduced consumer acceptability of fresh meat
• DFD: Dark, Firm, and Dry


  • Can be caused by fatigue, exercise, fasting, excitement, fighting. Occurs in beef and swine
• DFD Meat


  • Glycogen used during prolonged high stress period
  • Little glycogen remaining for anaerobic metabolism
  • pH and WHC remains higher than normal
• DFD Meat


  • Pros: Good for high moisture processed products, very juicy fresh meat
  • Cons: Bad for production of dry or semi-dry products, may have a metallic taste, environment promotes microbial growth
• Rigor Mortis


  1. Delay: Aerobic metabolism, ATP is still available, meaning muscles can relax

  2. Onset: Muscles get more stiff, creatine phosphate is being used

  3. Completion: No remaining creatine phosphate or glycogen for energy development, Actomyosin has formed from the permanent crossbridges of Actin and Myosin

  4. Resolution: Proteolytic degradation
• Time to rigor onset by species

  • Beef: 6-12 hours
  • Lamb: 6-12 hours
  • Pork: 1/4-3 hours
  • Turkey: < 1 hour
  • Chicken: < 1/2 hour
  • Fish: < 1 hour
• Toughening from Rigor


  • Skeletal (bone-attached) muscle can be prevented from massively shortening during a rapid chilling process
• Cold Shortening


  • When carcasses are too lean, cooling occurs too quickly. Rapid release of calcium from damaged SR. Severe contraction. Major issue if hot-boning carcasses.
• Beef topside muscle


  • Before (28 cm) and after (46 cm) SmartStretchTM stretch. The tenderness of the meat was improved by stretching up to 34% of its initial length.
• Thaw Rigor


  • Muscle is frozen pre-rigor and thawed. Calcium floods the muscle from the sarcoplasmic reticulum. Results in 66% shortening. Severe toughening and release of water.
• 3 States of Water

  • Bound
  • Immobilized
  • Free
• Bound Water


  1. 5% of total, not released during processing except ashing
• Immobilized Water


  16-17% of total, create multilayers of water: loosely bound as the distance from the bound water increase, some lost during cooking
• Free Water


  79% of total, lost as purge or drip during cooking
• Variation in Fluid Loss

  • Low
  • Intermediate
  • High
• High Temperature and Low pH

  Cause Protein Denaturation
• Protein Denaturation


  Decreases color and color stability, decreases water-holding capacity
• pH


  Isoelectric point (pI): At low pH, positive charges repel, at high pH, negative charges repel, at isoelectric point, balanced charges interact
• Protein denaturation and charge affect water holding capacity
• Glucagon


  Converts to Glucose
• Glycogenolysis:

  
  

  cut up glycogen to produce glucose
• 1 glucose molecule produces 36 ATP
• Glycolysis: cut up glucose
• Major Factors Affecting the Quality of Fresh Meat


  • Visual Appearance
  • Flavor
  • Juiciness
  • Tenderness
• Visual Appearance


  • Amount of Fat
  • Color
• Fresh Meat Pigments


  • Myoglobin (80-95%)
  • Globular protein (globin)
  • Non-protein heme complex, iron containing
  • Hemoglobin (from residual blood)
  • Cytochromes, catalase (oxidative enzymes, minor contribution)
• Pigment Concentration (mg pigment/g muscle)


  • Beef (4-10)
  • Lamb (4-8)
  • Pork/Veal (1-4)
  • Chicken (dark) (2-6)
  • Chicken (light) (<1)
• Factors Affecting Pigment Concentration


  • Species
  • Animal Age
  • Gender
  • Fiber type
  • Physical Activity
• Additional Factors Affecting Meat Color


  • Muscle pH
  • Rate of pH decline
  • Uneven chilling (heat ring)
  • Chemical state of heme iron in myoglobin
  • Type of packaging
  • Microbial contamination
  • Age of meat
  • Cooking
  • Curing