Muscle biology (Lec. 17-18)

Lectures 17-18: Conversion of Muscle to Meat

What are the primary functions of the muscles?

Structure/support, movement, maintenance of temp, & dietary protein source.

Smooth Muscle

Unstriated, elongated, & responsible for sustaining contractions in the vascular system + GI tract. It is non-voluntary (controlled by the autonomic nerve system).

Cardiac Muscle

Striated, short, branched fiber networks, & responsible for pumping blood to the body. Non-voluntary.

Skeletal Muscle

Striated, long, unbranched, & responsible for movement. Voluntary.

Myocyte

Muscle cell or fiber (long)

Myofibrils

Functional unit of muscle cell (medium)

Sarcomere

Building block unit of myofibrils (small)

Fasciculi

Bundles of myocytes (multi muscle sells each bundled)

The 3 layers of muscle tissue

1. Epimysium → external layer, wraps the entire muscle

2. Perimysium → Internal layer, wraps muscle bundles

3. Endomysium → Internal layer, wraps every muscle cell

T-tubles

Communication channel for the interior muscle fibers

Sarcolemma

Cell membrane, attaches muscle fibers to connective tissue

Sarcoplasm

Cytoplasm of muscle, stores glycogen & myoglobin (red color, stores oxygen)

Z line

Key primary structural element of myofibril

A band

Composed of both thick & think filaments

I band

Composed of only thing filaments

H-zone

Composed of only tick filaments

M line

Center of sarcomere, thick filaments are held together

Myofibrils

Basic unit of contraction inside myocyte, the contractile machinery of the cell. (skeletal muscle cell)

Fibrous proteins of Myofibrils

Actin (thin filament) & Myosin (thick filament)

Interaction between Action & Myosin

Calcium initiates muscle contractions, tells protein to release the Ca++ & get ready to bind.

How contractions work

Thick & thin myofilaments “slide” across one another, bringing Z-line closer together & shortening the H zone + I bands.

Exsanguination (Blood removal)

Interrupts the supply of O2 to muscles & shifts energy metabolism from aerobic to anaerobic pathway.

Muscle pH Decline

pH of meat will drop due to the buildup of lactic acid

Bound Water

Held tightly by charged hydrophilic groups on the muscle proteins

Immobilized water

Held tightly by weaker attractive forces near charged protein

Free Water

Held only by capillary forces, independent of charged proteins

Water Holding Capacity (WHC)

ability of meat to retain water during application of external forces (cutting, heating, grinding, or pressing)

pale, soft, & exudative (PSE) Pork

Caused by extremely rapid rate of pH decline, resulting in low muscle pH + high temp. Usually occurs when the animal is very excited.

Dark Cutting Conditons

Caused by depletion of muscle glycogen stores before harvest, usually results from cumulative effects or stress factors such as psychological, physical, or environmental

Rigor Mitors

Creatine phosphate & glycogen stores exhausted → slow depletion of ATD, extensibility, muscle shortening & permanent bridges of actomyosin.

The 3 phases of Rigor mortis

1. Delay phase: energy still present, muscle relaxed

2. Onset phase: Muscle almost uses energy, pH declining

3. Completion phase: No more energy available for muscle