Meat past exams and possible exam questions Flashcards
Effect of preslaughter stress on pigs and its affect on tenderness/quality of pork
acute preslaughter stress can lead to PSE - mainly affects pigs
PSE is pale, soft, exudative
- dry and poor textured meat once cooked
- increase in lactic acid ->low pH athigh temp -> denaturation of muscle -> lack of water binding (poor WHC) -> increase light scattering -> pale colour
- lowered processing yields, increases water loss and reduced juciness
Effect of preslaughter stress on beef cattle and its affect on tenderness/quality of beef
chronic preslaughter stress can lead to DFD - occurs mostly in red fibres e.g. beef
DFD is dark, firm, dry
- dry and sticky
- poor flavouring and processing characteristics
- increased spoilage potential and shorter shelf life
- low/no glycogen levels - > decreases lactic acid and meat not acidified properly -> high pH -> proteins don’t denature -> high WHC -> decreases light scattering -> darker
firm because fibres packed tightly
dry because water bound tightly
The effect of WHC on meat structure?
5% of water in muscles bound directly to hydrophilic groups on meat protein
95% of water in muscle is stored between the thick myosin filaments and thin actin filaments
therefore increase WHC -> swollen ->juicy and soft meat
Why does pH in muscle decrease with time?
?
as glycogen supply is used up ->accumulation of lactic acid (cant be removed) -> decreases in pH
What is the ultimate pH
pH is >6 while temperature is >35 degrees
pH is <6 before temperature gets to 12 degree
ultimate pH is around 5.5-6?
What is cold shortening?
the shortening of muscle sarcomeres
occurs when slow pH drop and fast temp drop
meat is chilled before RM and before glycogen is converted to LA -> big contraction not follwed by relaxation -> shortened sarcomeres -> results in tougher meat
Why electrical stimulation is used to overcome cold shortening
- application of an electrical current to carcasses of meat animals one hour after slaughter
- can match level of ES to chilling
- stimulates the contraction/relaxation cycle of muscles and depletion of ATP -> tender meat
Differences in vacuum packaging and modified atmosphere packaging
vacuum packaging
- removes all O2 from plastic bag then meat is sealed in bag impermeable to gas, anaerobic conditions
- great for storage and transport but not for presentation
Modified atmosphere packaging
- higher co2 and O2 in bag than in air
- enhanced O2 concentration encourges penetration of O2 further into meat
- CO2 inhibits undesirable microbial growth
concern is the increase shelf life can enable pathogenic bacteria to unsafe growth
Differences in PSE and DFD
PSE - pale soft exudative - dry and poor texture - acute stress - aminly in white fibre e.g. pig DFD - dry firm dark - dry, stick , poor flavouring and processing characteristics - chronic stress - mainly in red fibre e.g. cattle
Why does collagen make meat tougher?
as the amount of connective tissue in muscle (in which collage is a principle component) affects texture and tenderness
- lack of collagen/crosslinks -> poor texture -> tougher meat
What are the three pigments that colour meat?
How are they interrelated
myoglobin - purple - heme iron - reduced state (fe2+) oxymyoglobin - red - oxygenated form of myoglobin - reduced state (fe2+) metmyoglobin - brown - oxidized form of myoglobin - oxidised state(fe3+)
What is thaw rigor?
What is it’s effect on tenderness?
- severe type of rigor mortis that developed when muscle that was frozen pre rigor is thawed
- developed by sever contraction produced by sudden release of Ca2+ ions into sarcoplasm -> releases large amounts of meat juice (poor WHC) -> tougher meat
Describe the three main post mortem stages involved in conversion of muscle to meat
- acidification
- denatures proteins and myofibrillar proteins reach isotonic point -> negatively affects WHC (by exudating moisture from cut surface ->drip loss) and colour (increased light scattering -> pale and opaque)
Describe the three main post mortem stages involved in conversion of muscle to meat
- development of rigor
development of RM - the temperature at which muscles go into rigor affect tenderness
e.g. if high temp -> heat shortening -> denaturation in proteolytic calpain enzymes -> tough meat
Describe the three main post mortem stages involved in conversion of muscle to meat
- resolution of rigor/ tenderisation
- when muscles soften
- affected by sarcomere length, temperature, pH, ageing time, marinating and injecting, diet
What is the post slaughter tenderisation process for meat called ageing or conditioning? how is it done?
natural process of tenderisation when meat is stored post rigor done in two processes rapid phase (more important) - changes to myofibrillar component - attaches thin filament to Z disc - increases water soluble N compounds slower phase - structural weakening of intramuscular connective tissue
post slaughter tenderisation process for meat called ageing or conditioning - 3 chemical/physcial changes that occur?
- proteins of myofibril denature and weaken
- changes in connective tissue components of meat
- increase pH and WHC
post slaughter tenderisation process for meat called ageing or conditioning - enzymes involved?
calpains
- activated by calcium ions
- max activty in neutral - alkaline conditions
cathespins
- in lyosomes
- max activity if slightly acidic conditions
- degrades troponin T and collagen crosslinks etc
What are the differences in the proteins that make up thick and thin filaments of muscle microfibril?
thick - myosin
- 2 heads, neck and tail (fromed by two long strands wound together)
- forms crossbridges with heads
thin - actin
- globular molecules
- forms thin filaments with troponin and tropomyosin
both bind ATP but in different spots
Why is transport of animal to abattoir important for meat quality?
- selected, weighed and drafted on farm
- loaded (different animal groups from different pens)
- transported via road
risks - loading and unloading animals - difficult and stressful
- food and water deprivation
- animals fighting or other mishap injuries - can cause bruising, hemorraging, broken bones
- if animal dies - total loss of yield and eonomic
stresses involved in getting animals to slaughter
- removal from home environment
- loading and unloading
- long journey
- unfamilliar surroundings
- physical stresses - temperature, vibrations, speed, crowding, hunder, thirst, fatigue
- psychological stresses - mixing with unfamiliar animals in unfamiliar environment
5 major components of meat quality
yield and composition - determines how much there is to sell - higher yield -> more product-? more profit
appearance and technical characteristics ->appearance only criteria before buying
palatability - tenderness and juiciness interrelated, aroma and flavour interrelated
wholesomeness - safe to eat and beneficial to health
ethical quality - animal meat - sympathetic to animal welfare and environmentally friendly
conflicting problems with meat quality
- juiciness is linked to intramuscular fat (unhealthy)
- lean pigs linked to soft fat (healthier but not as supportitive
- nitrite in production of cured meats – gives attractive colour, inhibits growth of pathogenic bacteria but is implicated in development of some cancers
Genes affecting pork quality
the halothane gene
- susceptible pigs exhibit - extended and rigid limbs, raised bodys temps -> malignant hyperthermia -> fall in pH -> PSE
the rendement napole gene
- increases glycogen content -> converted to lactic acid after slaughter -> decreases pH -> breakdown proteins -> increase drip loss and cook loss -> pale meat (similar characteristics to PSE)
