Muscle to Meat

Briefly describe how ATP is generated within muscle…

*** Creatine phosphate ***

• Stores energy in phosphate bonds in resting muscle, made with ATP + Creatine. (ATP + Creatine → Creatine Phosphate + ADP)

• Creatine kinase facilitates the REVERSAL of this reaction once a muscle is contracted, giving energy to the now-active muscle

Briefly describe how glycolysis generates ATP:

An anaerobic and aerobic process; but when oxygen levels are low, pyruvate converts to LACTIC ACID 

• Very important in muscle to meat process 

• This anaerobic process increases production of lactic acid after slaughter… since animal is not breathing, but body is still trying to generate ATP, lactic acid will begin to build up in muscle 

• Essentially, body is trying to maintain homeostasis despite the animal being dead 

Describe what happens to muscle when an animal is bled, and how it affects meat production…

Animal is bled, circulation stops, no more delivery of oxygen to tissues

• Aerobic -> anaerobic metabolism, consumes ATP faster than it is produced 

• Lactic acid builds up in muscle (we want this)

• Increase in acid, decrease in pH to 5.5 (goal; if not met, get meat quality defects) ***** This is the pivotal point in meat production!!

  • Water content in meat also decreases as muscle fails to retain water

• Enzymes activated by acidic environment -> PROTEOLYSIS 

  • Changes flavor of the meat

• Myofibrillar protein (Z plates specifically) are broken down by activated enzymes

• Releases amino acids and peptides which react with the reducing sugars in the body

  • CHANGES FLAVOR 

  • INCREASES TENDERNESS

What is conditioning in the context of muscle breakdown after slaughter?

Within first few hours of slaughter, before rigor mortis, muscle is tender 

•Toughness sets in at rigor

•After several hours of storage the original tender state is restored. This is known as ‘conditioning’

Conditioning is closely related to structural breakdown of muscle proteins, by released endogenous proteases (calpains and cathepsins) which are activated by calcium

What are the PRE-mortem factors that can impact meat quality?

• Breed

• Genetics

• Energy level of diet

• Type of muscle

• Stress level

What are the POST-mortem factors that can impact meat quality?

Storage conditions

•Temperature, humidity, airflow

•Length of time ageing (want long for tenderization, but not so long that it spoils)

Processing conditions

•Tenderizing techniques

•Speed

What are the two main meat quality defects?

• Dark firm dry (DFD) meat

• Pale soft exudated (PSE) meat 

Describe DFD meat and why it happens…

• Caused by CHRONIC, LONG TERM STRESS prior to slaughter

  • Ex: issues during loading, prolonged travel time, long periods without food, etc.

• Chronic stress leads to increased cortisol; increased cortisol -> increased metabolic rate -> glycogen store depletion from muscles 

  • Less glycogen available for the normal process of acidification 

    • Less glycogen -> less lactic acid production -> less acidification -> less enzyme activation and proteolysis 

    • Body’s pH stays relatively the same (pH 6, target is 5.5); therefore, proteins stay intact, water holding capacity stays intact, and intracellular water reflects less light

      • This all leads to the meat’s darker, larger, more firm appearance 

Why does DFD meat matter if there’s nothing truly unhealthy about the meat?

Consumers eat with their eyes!

Reduced shelf life

• Microbes can grow more easily due to INCREASED water retention and DECREASE of spoilage competing bacteria that use glycogen

Not as good of flavour

• Proteins can't break down

• Lactic acid cannot interact with the by-products to create flavour

** Can be improved with better welfare

Describe PSE meat and why it happens…

Happens due to ACUTE burst of stress before slaughter (ex: electric goads, prolonged lairage time, animals fighting before stunning); always at the slaughter plant 

• Happens mostly in pigs (sometimes poultry) 

When an animal has acute stress, they have lots of adrenaline and their body heats up; also see a sharp increase in metabolic rate 

• pH most mortem goes down REALLY quickly, goes way below where it needs to be (pH - 4, target is 5.5)

• Glycogen stores deplete MUCH FASTER after slaughter, while carcass is still hot 

• Low pH and high temperature causes proteins to denature quickly → causes quick decrease in water holding capability → INCREASED EXUDATE ON CUT SURFACE

  • Makes meat look slimy 

  • Increases light reflection, making meat look pale

  • Common in pigs, who are prone to acute stress 

** when its cooked, shrinks SIGNIFICANTLY and becomes tough 

Why does PSE meat matter if there’s nothing truly unhealthy about the meat?

Consumers eat with their eyes!

• •Meat loses a lot of water content and continues to be “wet”

• •Difficult to cook

• •Potential condemnation for lack of consumer interest

• •Lost revenue

** Again, can be improved with better welfare at slaughter

How can we prevent DFD/PSE meat and improve tenderness?

• GENTLE/QUIET HANDLING

• Ramp usage

• No electric goads at loading/lairage, using gentle methods

• Access to food/water

• Breed stress resistance

• Reduce transport times where possible (go to the nearest slaughter plant)

• Don't mix animals – keep fighting to a minimum 

• Spray pigs with water to keep them cool

• Genetics

What are 3 ways we can improve meat quality at the slaughterhouse?

• Chilling / chilling methods

• Hot boning

• Electrical stimulation 

For chilling… remember, what are the MAX temperatures different types of meat can be chilled at?

• 7 C for red meat

• 4 C for poultry 

• 3 C for offal 

What is the current method of chilling, and how does it benefit meat quality?  What are its potential risks to meat quality?

Rapid chilling via refrigerated air once the carcasses are finished

• Helps to reduce bacterial growth, evaporative weight loss, and the potential for PSE…

• BUT can lead to “cold shortening”, which is when calcium is retained and concentrated in the sarcoplasm; induces muscle contraction resulting in toughness

When does cold shortening (CS) occur?  How do you prevent it?

CS occurs when muscle cools below 10°C before rigor mortis

Muscle fibres shorten by as much as 1/3 of original length; enzymes are kept from further breaking down the muscle, and the body is essentially kept in its rigor state 

• To prevent CS:

  • Beef and lamb: chilled at temps not below 10°C in the first 10h usually at 12 degrees ***

    • After that, can be gradually dropped to 7 C

  • Pork: chilled at temps not below 10°C in the first 3h – Poultry can be even shorter

    • CS DOESN’T REALLY HAPPEN IN PIGS AND POULTRY!!! Not really a red meat so = less sarcomeres 

How does the way carcasses are suspended in the cooler affect meat quality?

• Traditional way → carcass suspended by common calcanean tendon

• Improved way → hip suspension; suspended through obturator foramen instead 

  • Rump muscles, which go for a lot of money, are better stretched this way… more stretching improves tenderness of the meat 

  • Still does have disadvantages… carcasses less stable this way, more likely to fall on the floor

What is hot boning, and what are its advantages / disadvantages for meat quality? 

Hot boning: when the meat is cut BEFORE its chilled

Advantages:

• More efficient and quicker refrigeration of meat,

• Reduced evaporative weight loss (up to 1%),

• Less dripping in vac-pack

• Better colour

Disadvantages:

• Need to synchronize slaughter and boning

• Fat difficult to trim

• High hygiene standards

• Electrical stimulation required

What is “electrical stimulation” after slaughter, and how does it improve meat quality for hot boning?

Electrical current is passed through the carcass using an electrode node in the neck

• Sends low-voltage pulses of electricity that cause the muscle to contract really quickly 

Speeds up glycolysis and increases lactic acid production more quickly 

• Reduces the risk of CS by essentially speeding up rigor mortis and lets the meat age faster 

  • Then allows for faster chilling