Glycogen to lactic acid

PH falls from 7.2-5.5

actin and myosin form bond

in beef- gradually disappears after 24 hours

Pork: 6-12 hr

Chicken: 1.5 hour

Beef: 18-40 hr

Lamb: 16-24 hr

Before: 

PH 7.2

dark surface color

absence of fluid

sticky on mincing

high electrical resistance

slow penetration of salts

AFter: 

low ph 5.5

light color

exudes fluid

not sticky on mincing

low electrical resistance

rapid penetration of salts/sugars 

Ante Mortem

- physical stress

- health status

- genetics, exercise

Post mortem: 

- time/temperature chilling

- hot boning

- carcass suspension

- use of electrical stimulation 

- Chronic stress pre slaughter ( 24-48 hr) eg. transport, disease, diet

stress-> activation of the hypothalamic Pituitary Adrenal Axis ( HPA)-> release of glucocorticoids-> deplete glycogen storage-> inadequate lactic acid production -> high ultimate pH in meat

Advanced spoilage

not suitable for vacuum packaging or long distance transport

tough and tasteless

more common in pigs

Acute stress -> activation of sympathtic-adrenal- medulla axis ( SAM)-> release of adrenaline-> increased glycogenolysis -> high rate of lactic acid-> rapid fall in pH 

- excesive drip

pale

tougher on cooking

- can affect beef and lamb carcasses

- when temp reduced to 0-15C before the onset of rigor mortis, the sarcoplasmic reticulum cannot function properly and is unable to bind calcium in the sarcoplasm, because there is still ATP left in the muscle, the muscle contracts at the maximum extent causing the filaments of acting-myosin to slide over one another eliminating the I band of the sarcomere

- Pigs and poultry carcasses are not affected 

- type 1 red fibres: have slow contraction

type 2 white fibres: have fast contraction 

preventative measures: 

- electrical stimulation

- pre chilling techniques temperatures not to fall below 10C within 12 hr from slaughter

- carcass temp should half every 8 hours

electrical current throughout meat

stimulates muscle to contract=glycogen/ATP used  up

- speed up rigor mortis

- meat ages faster

BEnefits: 

- accelerates tenderness

- reduces storage times and weight loss

- allows rapid chilling

- promotes better flavour and colour

- avoids cold and thaw shortening

Advantages: more efficient and quicker refrigeration of meat

less dripping in vacuum pack

- better color

Disadvantages: 

synchronize slaughter and boning

- fat hard to trim when doing this

- hard to have high hygeine standards

suspended within 90 minutes of slaughter, for a minimum of 24 hours

- accelerates tenderness by 3 weeks at 2C 

influenced by the electrostatic charge of proteins

- at low pH proteins change their electrostatic charge and fail to attract water

- water loss can reach 16% at 18 days

amount and chemical nature of connective tissue/fat in the muscle

- the amount of shortening due to rigor mortis

- the extent of meat conditioning and ageing 

process of meat maturation that occurs through the action of endogenous enzymes

Factors affecting ageing:

- conditioning

- electrical stimulation

- pelvic suspension

- storage/temperature

- packaging 

- affected by fat content and the amount of water left in cooked meat

- over lean carcasses can fail to self baste

- depends on meat cut

- breed

- diet 

myoglobin oxygenated=blooming

DFD turgid muscle and poor penetration of oxygen

paleness is caused by increased scattering of light within meat 

depends on species, age, feeding

sheep: white,, hard

pigs: white, softer

horse: yellow, oily

cattle: cream/yellow, firm

Age: older cows-> yellower

Feeding: barley beef: pure white

grass beef: yellow

cod liver oil- orange 

species, 

sexual odours

uraemia

abscess

Diet

gangrene

drugs