Muscle to Meat
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How much glycogen does muscle at death contain?
What is the pH of muscle at death?
What is the term for stiffening of muscles after death?
What chemical reaction causes rigor mortis?
When does rigor mortis reach its maximum?
What chemical reaction occurs during anaerobic glycolysis?
Glycogen is converted into lactic acid
Does anaerobic glycolysis increase or decrease muscle pH? What is the new muscle pH?
Decrease - 5.5
Actin and myosin form the ... bond?
What happens to muscle after 24hrs?
Rigor mortis gradually disappears, autolytic ferments form and the pH of meat rises
List the differences between a normal carcase/24hrs later with regards to a) pH b) structure c) colour d) fluid e) texture on mincing
f) electrical resistance g) penetration of salts/sugards
- a) N = 7.2, 24hrs = 5.5
- b) N = closed, 24hrs = open
- c) N = dark, 24hrs = light
- d) N = absence of fluid, 24hrs = exudes fluid
- e) N = sticky, 24hrs = non-sticky
- f) N = high, 24hrs = low
- g) N = slow, 24hrs = rapid
What factors affect glycogen?
Exercise/training, diet, stress, health status
What is DMD?
Dark firm dry meat
What causes dark firm dry meat?
Chronic pre-slaughter stress (24-48hrs)
Describe how DMD occurs?
Stress --> low glycogen --> high pH (6.8) --> oxygen debt --> dark meat
Does DMD meat have a good or poor keeping quality?
Poor due to high pH
True or false: DMD meat has the same nutritive quality?
True but it is tough
What is DMD meat usually used for?
What does PSE stand for?
Pale soft exudative meat
What species does PSE occur more commonly in?
Poultry and pigs
What causes PSE meat?
Acute stress (within the last 8hrs)
Describe the changes that occur in PSE meat?
Accelerated glycolysis causes a rapid build up of lactic acid, and therefore a rapid fall in pH. This causes rapid onset of rigor mortis and excessive drip loss from cut surface and cooking.
How can we minimise DFD/PSE?
- Handle gently
- Use loading ramps
- Do not mix stock
- Good lairage design
- Ensure food/water is available
- Do not use sticks/goads
- Isolate aggressive animals
What is cold shortening?
This is when muscle cools below 10°C before rigor mortis and can result in shortening of 1/3 of original length
What is ageing/conditioning of meat?
The practice of holding carcases of meat cuts at chill temperatures in order to improve tenderness
What are two techniques used to speed up the ageing process of meat?
- Electrical stimulation
- Tenderstretch hanging
What is electrical stimulation?
When an electrical current is passed through meat - electrodes are placed not he neck of the carcase
How does electrical stimulation speed up ageing?
It stimulates the muscles to contract, using up ATP/glycogen, decreasing pH and speeding up rigor mortis.
List some benefits of electrical stimulation
- Accelerates tenderness/reduces ageing times
- Reduces storage times and weight loss
- Avoids cold and thaw shortening
- Allows rapid chilling
- Promotes better flavour and colour
- Allows hot boning
What type of meat is electrical stimulation used/not used in?
- Used - Beef and lamb
- Not used - pigs (causes PSE) and dark cutting beef
What area are carcases hung from?
The obturator foramen
How does stretching make meat better?
It tenderises the meat
What is setting?
Rigor mortis plus fat hardening
What species sets more firmly?
What can poor setting result in?
- Poor keeping quality
- Deep spoilage
- Often indicates illness
- Carcase loses shape which makes it difficult to butcher
- Usually a severe judgement on carcase
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