Meat

1
Meat

• Justin Shimek and Jun Kim
• FST 100A
• Discussion Hour 6

2
Meat Lecture Outline

• Today build on protein lecturesmeat as a
  complex structure and a commodity
• Definition of meat
• Regulation, Quality Grades, Safety
• Microstructure protein fibers/molecular motors
• Macrostructure the cuts
• Structure related to key quality factors
  tenderness, color, and Water holding capacity

3
Meat Definition

• General (historical)
• solid food, i.e. that which is not drink
• Intermediate (common)
• animal tissues
• may include game, poultry, fish
• Specific (USDA)
• the muscle of cattle, pigs, sheep, and goats

4
Meat Composition and Consumption

• USDA estimates 99 eat meat, 94 eat red meat
• American consumes average of 211.1 lbs/yr
• 51.6 red meat, 41.7 poultry, 6.7 fish

5
Meat Inspection

• Upton Sinclair, The Jungle (1906)
• Federal Meat Inspection Act of 1906
• Wholesome Meat Act of 1967
• USDA Food Safety and Inspection Service charged
  with meat (poultry egg) inspection
• purple stamp
• Eight voluntary quality grades in beef
• Prime, Choice, Select, Standard, Commercial,
  Utility, Cutter, Canner

6

• Muscle
• ends blend with tendon

Bundle of muscle cells

• Muscle cell (or fiber)
• surrounded by sarcolemma
• surrounded by thin connective tissue layer

Muscle fibril
Sarcomere (myofilaments)
Actin and myosin
Size
7
Principle Myofibrillar Proteins
know

• Actin
• small spheres arranged like string of beads
• two strings twisted together ? thin filaments
• Myosin
• shaped like golf clubs
• cluster ? thick filaments

8
The Sarcomere
know
Thick filament
Z-line
Z-line
Thin filament
9
Muscle Contraction
Karlsson, 1977
3
4

• 1) Rigor
• myosin binds actin
• 2) ATP association
• pops off actin
• 3) ATP hydrolyzed
• weak actin/myosin assn
• 4) Powerstroke
• ADP Pi disassociate

ADP Pi
ADP Pi
ADP Pi
ATP
ATP
1
2
10
Primal Cuts
11
Connective Tissue

• Amorphous substance with embedded fibers of
  collagen elastin
• Collagen
• white, doesnt stretch, 3 twisted ropes
• hot water melts collagen to gelatin
• Elastin
• yellowish, stretches, in heavy use muscles
• not greatly affected by cooking

12
Factors Affecting Tenderness
know

• 1) Connective Tissue
• More connective tissue, tougher
• Collagen and solubility, elastin
• Cooking decreases toughness
• 2) Actin Myosin
• In rigor, form stable cross-links
• Aging increases tenderness due to enzymatic and
  chemical breakdown
• Cooking proteins denature, microfibers
  coagulate, meat toughens

13
Postmortem Changes and Aging

• Rigor mortis
• Stiffening of carcass
• Lactic acid accumulation?pH decrease
• ATP gradually disappears
• The muscle becomes contracted as a result of
  these changes
• 2) Ripening or Aging
• Breakdown of proteins in myofibrils by enzymes
• Increase in tenderenss

14
Meat Color
know
N
N

• Myoglobin
• protein containing iron
• purplish-red
• Fe2
• Oxymyoglobin
• supermarket red
• Fe2 O2
• Metmyoglobin
• brownish-red
• Fe3 H2O

Fe2
N
N
Globin
O2
N
N
Fe2
N
N
Globin
H2O
N
N
Fe3
N
N
Globin
15
Water Holding Capacity(WHC)

• The bound water to the proteins hydrophilic
  groups
• The quantity of water immobilized within the
  network of actomyosin filaments
• At pI of actomyosin(5.4) Most of the charged
  groups are involved in the formation of salt
  bridges or cross-linkage ? tighten the muscle
  structure ? WHC decreases
• At above or below pI the cross-linkage are
  cleaved as result of charge repulsion
• Bivalent cation (e.g. Ca2) forming cross
  linkage