Post-mortem handling of carcasses and meat quality
18 important questions on Post-mortem handling of carcasses and meat quality
After dressing temperature drops as heat lost to surrounding air, rate of loss depends on factors such as
- Size of carcass
- larger carcasses cool slower
- Subcutaneous fat cover
- insulating as thermal conductivity low compared to muscle & bone
- Air circulation
- speed up process of chilling using high velocity refrigerated air [modern practise]
- To reduce microbial growth on carcass surface & reduce evaporative weight losses
- Rapid chilling can reduce weight loss from 2-3% in normal chilling to <1% over 1st 24h of storage
Three practical implications of different rates of carcass cooling
- Cold shortening
- Thaw rigor
- Heat shortening
Explain what cold shortening is & which animals (chicken, pork, lam & beef) will be the most prone & least prone to it.
- >freezing, lower the temperature the greater the effect
- problem likely to be most acute in situations where
- rigor development is delayed
- small volume os tissue are being chilled
- Chicken & pigs less prone to CS >> rapid rate of rigor onset
- Beef carcasses tend to cool slowly >> again less prone
- Lam carcasses small enough to cool rapidly & generally do not enter rigor quickly --> most prone to CS
- Oversimplification = modern systems cool some muscle, particularly those near the surface, rapidly enough to shorten in all species
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What is the role that calcium plays during cold shortening? How can cold shortening be prevented?
- Ca pump of SR not appear to function well at low temperatures
- Ca ions activate the actomyosin ATP-ase & lead to muscle contraction
"red" (oxidative) muscles have less well-developed SR than "white" (glycolytic) muscle
- "red" muscle tends more prone to CS - reduced ability to sequester Ca
- "white" fibres: Ca ion sequestering ability seems less reduced at <±10*C
- Exception = pig Longissimus dorsi (LD) muscle not appear prone to CS despite being composed largely of glycolytic fibres
Mitochondria also sequester Ca ions
- under anaerobic at low temperatures - ability reduced
- "red" muscle fibres have more mitochondria
- In redder muscles mitochondria release Ca ions that are not sequestered - also promoting contraction
What is thaw rigor
- Large amounts drip/exudate (30% muscle weight) lost during thawing
- contraction stimulated by rapid & huge release of Ca ions from SR on thawing
- Physical prevention of contraction can reduce toughening effects
Why would electrical stimulation be used?
- CS can only occur in pre-rigor muscle --> accelerating rigor development can enable faster chilling without meat toughening
- One way is by electrical stimulation (ES)
- Carcass temperature still high SR can take up Ca
previously released & muscle goes into rigor in relaxed state
- After rigor, muscle can no longer respond by contraction to cold stimulus caused by rapid chilling & there is no danger of toughening
There are different voltages
- low voltage
- 20-100V
- 20 sec
- applied immediately after exsanguination
- stimulates muscles via nervous system
- high voltage
- 500-1000V
- 90 sec
- applied up to 60 min post-mortem
- stimulates muscles directly
Would you recommend to use electrical stimulation on pigs, why or why not?
- CS less of a problem in pigs - rapid RM development
Explain what is heat shortening
Increased toughness attributed partly to shortening associated with contraction of muscle around rigor development
- celpains party denatured by high temperature & low pH = less tenderisation
Why would hot processing be performed & what are thee advantages & disadvantages?
- Conventional systems chill whole carcass to temperature of 7*C or less before subsequent cutting into smaller parts & further processing
- Can be waste of chiller capacity & energy consumption
- Due to size & irregular shape, whole carcasses cool unevenly
- Solution = process carcass while it is stil hot before chilling
- Process largely involves removal muscles from skeleton = hot boning/deboning/cutting
- Saves refrigeration space & energy
- May required less labour & reduce time needed to produce marketable meat
- Regarding yield = advantages & disadvantages
- Yield may be improved by 2% --> reduction in evaporative & drying losses
What are novel carcass suspension methods
- Stretching may increase sarcomere lengths & produce more tender meat
- conventional way to suspend carcasses during chilling is by hind legs using hooks passed behind Achilles tendon
- While some are in tension other are free to contract because of antagonistic way in which many groups of muscle opertate
- Pelvis suspension / hip free suspension - aitch bone
- LD, particularly lumbar area
- Muscles on outside of hip
Name 2 carcass suspension methods & describe how it affects meat texture
- Pelvis suspension / hip free suspension - aitch bone
- stretching results in more tender meat after cooking
- Tendercut
What are the three main functions of meat packaging
- Protects meat from contamination
- Inhibits certain microbial growth
- Reduced/eliminates evaporative weight loss
Explain how meat colour can be influenced by different types of packaging. Provide a few examples
- Consumers like meat to appear bright red --> associate colour with freshness
- Red is produced by creation of muscle harm pigments with oxygen
- covering meat with plastic films of different gas permeabilities can affect relation & alter colour of meat surface
- for fresh meat use oxygen permeable film
- Myoglobin (mb), oxymyoghobin (MbO) & metmyoglobin (metMB) & their haemoglobin equivalents are the three most common forms of meat pigments
- Mb = purple
- MbO = bright red
- MetMb = grey-brown
What are the 4 layers of meat/colour after cutting
- Cut surface
- Red
- Very thin layer metMb
- Mb
What can affect the thickness of MgO layer (besides oxygen)
- Storage temperature can also affect thickness of MbO layer
- After ±2-3 days in air, MbO at surface gradually starts to oxidise to metMb
- When around 20% surface pigment is oxidised change is enough to cause consumer discrimination
- colour stability very sensitive to temperature
- different between meat storage at 0*C compared to 5*C = significant
- browning being postponed from 48 hours to 1 week
Major role of plastic films in influencing appearance of meat is to control gas atmospheres in contact with its surface - influence reaction of heat pigments. Neme 3 important gasses.
- Oxygen
- oxygen oxygenates/oxidises pigments
- influences differential growth of aerobic & anaerobic bacteria
- Carbon dioxide
- inhibits some undesirable bacterial growth - mainly by extending the lag phase
- Nitrogen
- Inert & sometimes used as 'ballast' gas to overcome problem of high solubility of carbon dioxide in water (meat)
What are the different plastics that can be laminated together to benefit from their combined properties
- Polyethylene (sealing ability)
- Ethyl vinyl alcohol (gas impermeability)
- Nylon (strength)
There are 3 synthetic antioxidants commonly used, namely
- Propyl gallate (PG)
- Butylated hydroxyanisole (BHA)
- Butylated hydroxytoluene (BHT)
note: not allowed in meat by some countries
various mechanisms & substances (in body) protect against oxidation - vit C & vit E (can also add to the feed)
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