What happens during the delay phase?
- Calcium is still being maintained in the SR
- Normal supply of ATP
- Aerobic metabolism at beginning, but then switch to anaerobic as oxygen stores deplete
What happens during onset?
- ATP depletion
- SR leaks calcium; begins contraction
What are the ranges for time to complete for beef, pork, and chicken?
- Beef - 18-24 hrs
- Pork - 6-12 hrs
- Chicken - 0.5-1.5 hrs
What causes chicken to reach completion faster than pork or beef?
Does not have a high oxygen holding capacity because of fast-twitch muscle composition
Describe “thaw rigor”.
- Pre-rigor freezing
- Leads to very severe contraction
Describe “cold-shortening” and what we do to prevent it.
- Result of rapid chilling
- Causes meat to be very tough
- To avoid be either use high-temperature conditioning or we freeze slowly
- Electrical stimulation as well
What temperature range can lead to muscle shortening, proteolytic activities, and microbial growth?
77-98 oF
What temperature does minimum shortening occur?
61 oF
What does pre-rigor cooking lead to?
- Heat induced contraction
- Myofibrillar fracturing
- Lack of lactic acid
What are the physical limits of contraction?
- Thick filament will run into z-line if skeleton is not resisting contraction
- Muscle attachments to bone
How does pre-rigor grinding improve protein solubility and water binding ability?
- Incorporates oxygen into meat
- Terminates contractile processes of the meat pieces
Describe “pelvic suspension”.
- Hang carcass from hip
- Shortens sirloin tip sarcomeres (less tender)
- NY strips become more tender
Describe “tender stretch”.
- Sever connection between vertebra
- Improves tenderness of steaks
- Takes effort and has potential for microbial growth
What are the downfalls of pre-rigor boning/hot stripping?
- Causes excessive shortening
- Reduces tenderness
- Reduces functional properties (water binding, solubilizes proteins, etc.)
How does electrical stimulation improve tenderness and color development?
- Avoid cold shortening
- Rapid pH decline
- Accelerated rigor onset/shortened delay phase
How does rigor affect meat functional properties?
- Less water binding from muscle shortening
- Rigor bridges of polyphospate
- pH decline (5.6)
- Proteolysis - severing of myosin head (needs to be intact for emulsification)
