Meat Science and Meat Hygiene Flashcards
who leads world in beef, poultry, pork
- USA leads in beef
- China leads in poultry and pork
composition of skeletal muscle tissue
- 74% water
- 19% protein
- 5% lipid
- 1% carbohydrates
- 1% ash
composition of protein in muscle tissue
- 2% stromal protein
- 5.5% sarcoplasmic protein
- 11.5% myofibrillar protein
what is stromal protein
- connective tissue or support proteins (collagen, elastin)
- has role in meat toughness vs tenderness
what is sarcoplasmic protein
- aerobic and anaerobic metabolic enzymes, myoglobins
what is myofibrillar protein
- contractile proteins
- myosin (43%) - has role in juiciness, flavor, water holding capacity of meat
- actin (22%)
- other myofibrillar protein (35%)
beneficial roles of lipids in meat
- tenderness
- juiciness
- flavor
bad roles of lipids in meat
- rancid taste
- impairment of water holding capacity of meat
low levels of intramuscular fat results in
- dry meat with low taste
what is in the carbohydrate portion of skeletal muscle tissue
- ATP
- creatinine phosphate
- glycogen
what type of iron is more readily absorbed in meat
- the heme iron from meat is more readily absorbed as a nutrient, and heme iron accounts for 40-60% of total iron
what are directly involved in contraction in living muscle
- calcium, magnesium, sodium, potassium
what contribute to muscle fiber contraction post mortem
- magnesium and calcium
which species has lowest lipid %
cod
what does skeletal muscle consist of
- 10% connective and fat tissues
- 90% muscle cells and fibers
what are the 3 levels that connective tissues are distributed in muscles
- endomysium - surrounds each muscle fiber
- perimysium - surrounds each bundle of muscle fibers
- epimysium - surrounds muscle as a whole and is an extension of the tendon
what part of the muscle cell occupies nearly the entire intracellular volume
myofibrils
what is the contractile unit of the muscle fiber
sarcomere
features of muscle cells
- multinucleated
- spindle shaped
- 10-100 micrometers diameter
- elongated (long cell) - few mm to several cm
muscle contraction mechanism
- action potential from motor nerves
- ATP, calcium, magnesium
- actin slides over myosin filaments via climbing and falling onto myosin for contraction and relaxation respectively
- ATP required during both climbing and falling
what is significant about lysosomes
may be significant in converting muscle to meat
what does high mitochondrial density indicate
- aerobic metabolism
- high mitochondrial density = dark and red meat
- aerobic metabolism associated with red pigmented iron containing protein (myoglobin) in the sarcomere
what do lipid droplets serve as
indicators of quality meat during meat grading
what is important about glycogen
the preslaughter depletion of glycogen is important in meat quality
bands = protein in muscle or meat
- A band - thick, myosin
- I band - only thin filaments
- Z disc - dark thin line in middle of I band, contains zig zag elements than anchor ends of thin filaments
- M disc - darker line in middle of A band, contains protein myosin, connects centers of thick filaments
what are sarcomere lengths related to
toughness of the meat
what part of the cytoskeletal framework contributes to toughness of meat
T filaments (remain after thick and thin filaments stretched beyond their overlap)
two types of death after slaughter
- somatic death (immediate)
- cellular death (3-4 hours later)
biochemical changes during post mortem for conversion of muscle to meat
- lack of nutrient supply –> aerobic metabolism stops
- decline in body temp
- buildup of metabolic waste in cells
- anaerobic metabolism
- increased lactic acid levels in muscle cells
- decline in pH of muscle cells
- rigor mortis
- proteolysis of muscles by lysosomal enzymes (muscle aging = meat ripening)
- color change in muscle from purple to bright red
what biochemical processes do muscle undergo to become meat
- rigor mortis
- due to decline in ATP levels
what determines the color of meat
concentration of myoglobin in the muscle fiber
what happens within 24 hours after death to meat color, glycogen content, lactate production, pH
- glycogen –> lactic acid
- glycogen > 50 mmol/kg in live animals –> <10 mmol/kg in meat
- lactic acid < 10 mmol/kg in live animals –> >100 mmol/kg in meat
- muscle pH goes from 7.0 to 5.6 due to lactic acid
- muscle color - purple to bright red (pH 7 –> 5.6)
normal meat
- high lactate production
- pH 5.6
- normal pH or ripened meat
dark colored meat
- abnormally low lactate production
- pH 6-6.5
- dark, firm, and dry (DFD) meat
pale colored meat
- abnormally very high lactate production
- pH 5.2
- pale, soft, and exudative (PSE) meat
which species is DFD meat more common
cattle
causes of DFD meat
- starvation
- beef stress syndrome, alarm reaction of general adaptation syndrome
- limited lactic acid production postmortem
to prevent DFD meat
- feed and rest for 24-48 hours prior to slaughter
which species is PSE meat more common
pigs (hereditary)
causes of PSE meat
- very rapid glycolysis due to antemortem excitement or long postmortem holding time before chilling
- huge lactic acid production leading to rapid pH decline while carcass still warm
abnormally low pH of PSE meat causes
loss of color, firmness, water holding capacity
4 stages of rigor mortis
- pre-rigor (0-8 hrs), absent stage, delay phase
- onset (8-12 hrs), present stage, onset phase
- rigor mortis (12-24 hrs), complete stage
- resolution of rigor mortis (24-72 hrs), final, completion, passed, resolved stage
what happens in pre rigor
muscle still relaxed and flexible due to storage of ATP and creatinine phosphate
what happens in onset
stored ATP used up and muscle starts to lose flexibility
what happens in rigor mortis
muscle energy depleted, no way to regenerate it, full rigor mortis sets in, muscles completely stiff
what happens in resolution of rigor mortis
stiffness dissipates and muscles loose stiffness and is ready for fabrication
what affects time for rigor mortis to activate or onset
- linked to depletion of ATP in muscle
- occurs more rapidly in the old and young due to lower muscle mass
how is aging of meat done
keeping meat in chilling room at temperatures around 3 C
endogenous enzymes for tenderization of meat
- cathepsins
- calpains
exogenous enzymes for tenderization of meat
- proteinases (cysteine endopeptidases)
- derived from plants - papain (papaya), bromelain (pineapple), ficin (fig)
how do catheptic enzymes cause tenderization of meat during aging
- destroy collagenous connective tissue of the muscle
ideal meat tenderizer
a proteolytic enzyme with specificity for collagen and elastin in the connective tissues at the low pH of meat which would act either at low refrigerator temps or high cooking temps
three methods of storing meat for aging/ripening
- dry aging - store in cooler without packaging
- wet aging - packaging in vacuum bags
- proposed stepwise aging - dry then wet aging
4 criteria for meat quality grading
- marbling - measure fat distribution in ribeye muscle
- texture - determined by size of muscle fibers and bundles
- color
- maturity - A (young) to E (old), determined by degree of cartilage ossification at tips of dorsal spine of sacral/lumbar/thoracic vertebrae
marbling - grade, eating experience, type
- grade –> prime, choice, select
- eating experience –> juiciness, tenderness, flavor, texture
- types - fine, medium, coarse
8 US beef grades
- prime
- choice
- select
- standard
- commercial
- utility
- cutter
- canner
utility, cutter, canner grades of beef
- too much signs of aging
- too little intramuscular fat (too little marbling)
- too low quality for cooking on own
- usually sold to be used as an ingredient in industrial food processing -> hot dogs, dog food, etc
acceptable levels of fat in meat
3% to 7.3%
relationship between marbling, grade, meat palatability
greater marbling = higher quality grade = higher expected meat palatability
meat quality is described by 4 terms
- satisfaction by consumers
- nutritional qualities
- hygienic qualities (safety)
- serviceability (ease of use, price, etc)
one of primary casues of consumer failure to repurchase beef
variability in tenderness
