Meat Science & Hygiene Flashcards
What countries are responsible for most of the meat production in the world?
USA - beef
CHINA - poultry and pork
What are the 3 major components of protein in meat?
- stromal - connective tissue support
- sarcoplastic - aerobic and anaerobic metabolic enzymes, myoglobins
- myofiber - contractile myosin and actin
What role do stromal protein and myosin have in meat?
STROMAL = toughness vs. tenderness
MYOSIN = juiciness, flavor, water-holding capacity
What beneficial roles do lipids have in meat? Harmful roles?
BENEFICIAL - tenderness, juiciness, flavor
HARMFUL - rancid taste, impaired water-holding capacity
What results with low levels of intramuscular fat?
- dry meat with low taste
- marbled meat preferred
What are the 3 major components of carbohydrates in meat?
- ATP
- creatinine phosphate
- glycogen
What does ash contribute to meat? What ions are involved in living and postmortem muscle contraction?
iron heme (readily absorbed, makes up 40-60% of total iron)
- LIVING = calcium, magnesium, sodium, potassium
- POSTMORTEM = calcium, magnesium
What are the 2 major components of skeletal muscle?
10% connective/fat tissue; 90% muscle cells/fibers
What are the 3 layers of connective tissue in skeletal muscle?
- ENDOMYSIUM - surrounds each muscle fiber
- PERIMYSIUM - surround bundles of muscle fibers
- EPIMYSIUM - surrounds whole muscle and acts as an extension of tendon
What makes up most of the intracellular volume of muscle cells/fibers? What is the contractile unit?
myofibrils
sarcomere
What is the general structure of muscle cells?
- multinucleated
- spindle-shaped
- elongated cells from a few mm to several cm
Muscle cell:
How does muscle contract?
action potential from motor nerves cause contraction allowing actin to use ATP, calcium, and magnesium to slide over myosin filaments and then relax upon depletion of energy
- ATP is required for contracting and relaxation
What organelle is responsible for the conversion of muscle to meat?
lysosome
What is a high number of mitochondria in meet associated with?
higher concentration of myoglobin, making the meat dark red
What serves as an indicator of quality meat for grading? Depletion of what polysaccharide is important to meat quality?
lipid droplets
glycogen
What is the length of the sarcomeres and cytoskeletal framework associated with?
toughness of meat
What 2 types of death occur at slaughter?
- somatic death - immediate, cells are still alive due using glycolysis
- cellular death - 3-4 hr later
What 4 changes in the body occur during somatic death and cellular death?
SOMATIC:
1. brain stops regulating the body
2. heart stops circulating blood
3. lung stops pumping oxygen
4. immune system stops surveillance
CELLULAR:
1. lower body temperature
2. changes in eye
3. changes in skin
4. changes in muscles
What cellular mechanism is stopped upon cell death?
lack of nutrient supply (glucose and oxygen) causes the stop of aerobic respiration and the buildup of metabolic waste in cells (lactic acid)
What key change happens to postmortem muscle development? What causes this?
rigor mortis —> decline in ATP
What 3 changes develop following the switch to postmortem anaerobic metabolism? What does this lead to?
- ATP level declines
- creatine phosphate level declines
- glycogen breakdown - glycolysis
- increase in lactic acid levels
- decline in pH
- rigor mortis
- proteolysis of muscles by lysosomal enzymes
- color change
What color change occurs to postmortem muscle?
purple —> bright red or pink
- meat ripening due to aging
How is meat classified according to color?
RED - high levels of myoglobin; beef, veal, lamb, mutton
WHITE - lower levels of myoglobin; pork, poultry, game, fish, shellfish
(it is believed that white meat is healthier than red meat)
What 3 changes occur within 24 hours of death?
- glycogen reduced into lactic acid (glycogen < 10 mmol/kg and lactic acid > 100 mmol/kg in meat)
- muscle pH decreases from 7 to 5.6 due to lactic acid accumulation
- color change from purple to bright red/pink
How does the pH and lactate production compare in normal meat, dark meat, and pale meat?
NORMAL (bright red/pink) - 5.6, high
DARK - 6.0-6.5, abnormally low
PALE - 5.2, abnormally high
In what animals is it common to have dark, firm, and dry meat? How does this affect pH?
cattle
pH remains 6.0 (abnormally high) due to limited lactic acid production - good environment for microbial growth
What are 2 causes of dark, firm, and dry meat? How can this problem be solved?
- starvation - extended transport without feed depletes muscle glycogen
- beef stress syndrome - alarm reaction to general adaptation syndrome (fight or flight)
feed and rest for 24-48 hours prior to slaughter
In what animals is it common to have pale, soft, and exudative meat? What are 2 causes? What does this lead to?
pigs (hereditary)
- rapid glycolysis due to excitement antemortem or holding on kill floor before chilling
- huge lactic acid production while temperature is wark
rapid pH decline (5.2) causing loss of color, firmness, and water-holding capacity
What are the 4 stages of rigor mortis?
- pre-rigor (0-8 hr) - absent/delay stage where muscle is still relaxed and flexible due to ATP and creatine phosphate storage
- onset (8-12 hr) - present stage where the stored ATP is used up and muscle loses its flexibility
- rigor mortis (12-24 hr) - complete stage where all muscle energy is depleted and there is no way to regenerate it, making it completely stiff
- resolution (24-72 hr) - final stage where stiffness dissipates and muscle loses its stiffness and is ready for fabrication
Where is meat kept while it is aged? What is the onset of rigor mortis linked to? When does it occur more rapidly?
chilling room around 3 C
rate of ATP depletion
very young and older animals due to their lower muscle mass
What is essential for the ripening and tenderization of connective and contractile proteins in muscle? What are the 2 types?
enzymatic degradation
- ENDOGENOUS ENZYMES - cathepsins, calpains
- EXOGENOUS ENZYMES - proteinases, cysteine endopeptidases derived from papain, bromelain, and ficin
What would be the ideal meat tenderizer?
proteolytic enzyme with specificity for collagen and elastin in connective tissue at the low pH of meat and low/high temperatures
What is dry-aging? Wet-aging? How care they commonly combined?
DRY - carcasses stored in cooler without protective packaging at 0-3 C for 10-28 days with critical humidity and air velocity control
WET - carcasses packaged in vacuum bags at 0-3 C until frozen or consumed without the humidity and air velocity control required; tight vacuum sealing essential
DRY-THEN-WET - initial carcass holding in a cooler for early postmortem periods and fabricated into primals and further aged under vacuum packaging
Why are meats graded? What 4 criteria is it based on?
helps setting price value
- marbling - fat distribution in ribeye (number and texture of fat distribution)
- texture - fine vs. coarse depending on size of fibers or bundles visible on transversely cut surface
- color
- maturity - A = young; E = old (based on cartilage ossification at the tips of the dorsal spine of sacral, lumbar, and thoracic vertebrae
What are the 3 top ranks of marbling? What other qualities affect meat grading?
- prime
- choice
- select
- fine is preferred (not so much medium or coarse)
juiciness, tenderness, flavor, texture
What is considered the most luxurious, indulgent steak?
Wagyu ribeye
What are the 8 US beef grades? What are the last 3 levels commonly used for?
- prime
- choice
- select
- standard
- commercial
- utility
- cutter
- canner
ingredients/industrial food processing (hotdogs, dog food) - too much signs of age, too little intramuscular fat, too low quality for cooking on its own
Grading score, age vs. marbling:
- age: A (young) to E (old)
- commercial grade: older, usually over 2 years old, meaning the meat is less tender and more chewy
What concentration of fat is most acceptable? What happens if the percentage goes above?
3-7.5%
health issues
Meat grades vs. palatability:
high marbling = higher quality = higher palatability
What 4 terms generally describe meat quality?
- satisfaction by consumers - color, texture, juiciness, tenderdenss, flavor
- nutritional qualities - fats, carbohydrates, proteins
- hygiene qualities - product’s capacity to be safely consumed without exposing the consumer to biological, chemical, and physical hazards
- servicability - ease of use, ability to be processed, prices
