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How much glycogen does muscle at death contain?
1%
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What is the pH of muscle at death?
7.2
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What is the term for stiffening of muscles after death?
Rigor mortis
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What chemical reaction causes rigor mortis?
Anaerobic glycolysis
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When does rigor mortis reach its maximum?
20-24hrs
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What chemical reaction occurs during anaerobic glycolysis?
Glycogen is converted into lactic acid
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Does anaerobic glycolysis increase or decrease muscle pH? What is the new muscle pH?
Decrease - 5.5
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Actin and myosin form the ... bond?
Actomysin bond
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What happens to muscle after 24hrs?
Rigor mortis gradually disappears, autolytic ferments form and the pH of meat rises
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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
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What factors affect glycogen?
Exercise/training, diet, stress, health status
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What is DMD?
Dark firm dry meat
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What causes dark firm dry meat?
Chronic pre-slaughter stress (24-48hrs)
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Describe how DMD occurs?
Stress --> low glycogen --> high pH (6.8) --> oxygen debt --> dark meat
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Does DMD meat have a good or poor keeping quality?
Poor due to high pH
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True or false: DMD meat has the same nutritive quality?
True but it is tough
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What is DMD meat usually used for?
Manufacturing purposes
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What does PSE stand for?
Pale soft exudative meat
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What species does PSE occur more commonly in?
Poultry and pigs
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What causes PSE meat?
Acute stress (within the last 8hrs)
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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.
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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
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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
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What is ageing/conditioning of meat?
The practice of holding carcases of meat cuts at chill temperatures in order to improve tenderness
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What are two techniques used to speed up the ageing process of meat?
- Electrical stimulation
- Tenderstretch hanging
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What is electrical stimulation?
When an electrical current is passed through meat - electrodes are placed not he neck of the carcase
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How does electrical stimulation speed up ageing?
It stimulates the muscles to contract, using up ATP/glycogen, decreasing pH and speeding up rigor mortis.
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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
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What type of meat is electrical stimulation used/not used in?
- Used - Beef and lamb
- Not used - pigs (causes PSE) and dark cutting beef
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What area are carcases hung from?
The obturator foramen
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How does stretching make meat better?
It tenderises the meat
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What is setting?
Rigor mortis plus fat hardening
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What species sets more firmly?
Sheep
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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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