31. Postmortem Changes In Meat, Aging Of Meat, Autolytic Changes And Their Evaluation Flashcards
PM changes are generally related to ?
- Key structural properties of striated muscle
- Structural and biochemical changes in the muscle
- Meat and carcass quality
- Factors that affect PM changes
What factors affect PM changes include;
Nutrition, stress, exhaustion, shock, trauma, transport, temperature, humidity, environment, handling before slaughter and the housing system
Which are the 3 types of postmortem changes ?
Anaerobic glycogenolysis
Rigor mortis
Ageing of meat
What is the process of anaerobic glycogenolysis?
From 1mol of glycogen -> CO2 + H2O + 39mol ATP (muscle relaxation).
In case of no O2 present; ATP is produced from creatinine phosphate -> breaks down glycogen to lactic acid -> lowers pH and firmer meat
What is rigor mortis?
Muscle stiffening. Converts muscle to meat due to ATP depletion (low glycogen storage).
The lower glycogen storage the faster rigor mortis
What is the consequences to meat with rigor mortis?
Causes a decrease in pH, change in protein conformation and a reduced ability to bind water
What is onset of rigor mortis?
1-6h generally
What is it that determines the end of rigor mortis and what does it lead to?
That lactic acid is degenerated/converted into CO2 and H2O -> increase of pH.
After end of rigor mortis - meat becomes soft again and can hold water
What factors may affect rigor mortis?
Pre- slaughter stress; disease depleting glycogen storage leading to early RM and increased pH.
Post-slaughter; excessive chilling -> cold shortening -> tough meat
Why is meat being aged and for how long ?
To allow enzymes to break down muscle -> increased texture and flavor.
Fresh beef is aged from few days to weeks
What are technological properties that’s happening in meat that’s allowed to be aged?
- Dissociation of actin-myosin complex
- Proteolytic enzymes break down myofibrilsr proteins into peptides and AA
- Degradation of lactic acid -> meat becomes tender, increasing water binding capacity.
How can meat be aged/tenderized and which is the most common?
Drying of wet aging (most common)
What are some other methods for tenderization of meat?
- Physical tenderization; dissociation of actinomyosin complex, mechanical destruction of muscle.
- Electrostimulation, massage
- Enzyme degradation with synthetic enzymes (Proteolytic enzymes of mold, bacteria, pepsin and trypsin)
What factors may play in when aging meat ?
Species and temperature can increase aging of meat
What is autolysis of meat?
Self digestion of tissue enzymes
Why does autolytic changes occur?
Due to MO contamination, degradation of LA to CO2 + H2O, degradation and oxidation of fat.
What are some pathogens that may cause spoilage (autolytic changes) in meat?
Listeria monocytogenes, pseudomonas aeruginosa, Flavebacterium etc.
At what stage is there a change in the microflora that favors psychtrophic bacteria’s?
During cooling of carcass. Bacteria like these grow at 5-7 degrees and lower
In what way is the bacteria responsible for the changes of meat during microbial spoilage, what does it lead to?
By their production of proteolytic and lipolytic enzymes + slime, causes an unwanted change in color, flavor and taste
What are qualitative deviations of meat?
PSE, DFD, PSS
What are the evaluation methods for autolytic changes?
- Ammonia content – Conway’s content (indicator turns red in case of +)
- Estimation of acid value of fat – hydrolytic changes in fat – titration with KOH
- Estimation of tbars value (tiobaribituic acid) – sensory evaluation (off-flavor, smell, pink color)
