Food Comm- Red Meats

  1. What are the three types of muscle?
    Smooth, Cardiac, Skeletal
  2. What type of muscle is usually used as meat?
    Mostly skeletal
  3. What are the subunits of skeletal muscle?
    Fascilces- each fascicle are bundles of individual muscle fibres
  4. What is muscle?
    Specialized soft animal tissue composed of protein filaments that slide over each other and in the process, generate forces that can result in movement or motion
  5. How is mechanical energy produced in muscles?
    Chemical energy stored in molecules are released to produce mechanical energy or motion
  6. What is the major molecule in which hemical energy is stored?
    The major molecule in which chemical energy is stored or derived is ATP or adenosine triphosphate- each high energy bond releases 11kcal of energy
  7. How much energy is released from ATP?
    Each high energy phosphate bond releases 11kCal of energy
  8. What is smooth muscle?
    • Responsible for contractions in hollow vessels (blood vessels, lungs, GIT, bladder, uterus)
    • Most abundant (represents ~55-65% of the total muscle)
    • Non-striated (do not have the striped appearance displayed by the others)
  9. What is cardiac muscle?
    • Least abundant of the muscle with content of ~1.5-2% 
    • striated and the striations are highly branched and disorganized which enables rapid communication
    • Considered as the most important of the three types
  10. What is skeletal muscle?
    • Voluntary muscle
    • Muscles associated with the skeletal system
    • The proportion rances from 25-45%
    • They are referred to as 'voluntary muscles' because their action requires conscious' effort to make them happen
  11. What are voluntary muscles?
    Skeletal muscles
  12. What are the 3 types of proteins associated with red meat muscles?
    Sarcoplasmic, myofibrilar, connective tissue
  13. What are sarcoplasmic proteins?
    • Mainly H2O-soluble globular proteins, enzymes and Mb
    • Levels of sarcoplasmic proteins are almost same in fish, poultry, beef, and pork because they all have the same functional classes of enzymes to enable them to carry out the same metabolism
  14. What are glycolytic enzymes?
    • Type of sarcoplasmic protein
    • Leads to pH decline in muscle, so in the post-mortem animal, this shows as quality changes
  15. What are proteolytic enzymes?
    • Type of sarcoplasmic protein
    • Calpains and cathepsins
  16. What are calpains?
    Calcium activated proteases (break down muscle proteins)
  17. What is the purpose of proteolytic enzymes?
    Act to tenderize muscle/meat via breakdown
  18. How does proteolysis influence meat flavour?
    Proteolysis can form low molecular weight peptides and amino acids to influence meat flavour; also lipase can break down fats in the muscle to form free fatty acids that can also influence the flavour
  19. What is the purpose of heme in Mb?
    Responsible for colour of meats--> when it binds to O2 (NO); when Fe i form Fe2+ <--> Fe3+ +e-
  20. What is the purpose of the globin part of Mb?
    Even though it has no colour, it stabilizes or protects heme, and thus provides indirect effect on meat colour
  21. What determines the color of the flesh?
    The amount of myoglobin present in the flesh will determine the colour; the more myoglobin, the stronger the colour
  22. What is a higher Mb content related to in the animal?
    The higher Mb content relates to O2 requirement of the animal and energy production
  23. What is muscle fiber type I?
    Red in colour, high in Mb, contracts slowly, generates ATP via oxidation, degrades ATP slowly, useful for extended work
  24. What is muscle fiber type IIa?
    Red in color, high in Mb, contracts faster than type I, generates ATP via aerobic oxidation, breaks down ATP rapidly, useful for moderate level activities
  25. What is muscle fiber type IIb?
    White, low in Mb, high in glycogen, low in ATP, splits ATP rapidly, fatigues easily, useful for short burst of activity
  26. What are the 2 principle muscle proteins?
    Actin and myosin
  27. What does myosin look like?
    Myosin has several small protrusions called cross-bridges
  28. How does actin appear in the muscle?
    The actin strand is intertwined as a complex with a thin, ribbon-like protein called tropomyosin, and a smaller molecule, called troponin
  29. What is titin?
    • Another myofibrillar protein
    • Large protein and is responsible for the elasticity of muscles?
  30. What is titin attached to in the muscle?
    Titin connects the Z line to the M line in the sarcomere and is important in the contraction of muscle tissues, and is involved in restoring resting sarcomere length when the muscle relaxes
  31. How is actomyosin formed, and then degraded?
    • Actin binds troponin and tropomyosin to form a complex that does not bind myosin.  However, when nervous impusles cause release of Ca2+ ions from the sarcoplasmic reticulum into the sarcoplasm, which bind to troponin and cause tropomyosin to be dislodged from actin.  When tropomyosin is dislodged, myosin can then form the ACTOMYOSIN complex with actin via the cross-bridges
    • At the end of nervous impulses, Ca2+ ions floating around in the sarcoplasm are re-absorbed into the sarcoplasmic reticulum.  In the absence of Ca2+, tropomyosin and troponin bind to actin to displace myosin from the ACTOMYOSIN COMPLEX
  32. How does a muscle contract?
    All of the myosin cross-bridges bind to the exposed actin and drag the actin fiber along like a ratchet
  33. How much of total muscle proteins are sarcoplasmic proteins?
  34. What are sarcoplasmic proteins?
    Sarcoplasmic proteins include enzymes of glycolysis and glycogenolysis and others such as creatine kinase, AMP deaminase, proteinases as well as the O2 storage protein Mb
  35. What is the most abundant enzyme in the sarcoplasmic proteins?
    • Glyceraldehyde 3-phosphate dehydrogenase
    • Makes ~20 of the total sarcoplasmic protein fraction
  36. What are stromal proteins?
    • Connective tissue
    • High tensile strength protein molecules that are attached to structures like bones
    • They facilitate transmission of contractions from muscle fibers to result in movements of the bones to which they are attached
  37. What are the main connective tissue proteins?
    Collage, elastin, demosine
  38. What is collagen?
    • Polypeptide with high glycine and proline (hydroxyproline) content
    • Small size of glycine enables the polypeptie chain to be coiled into a long chain known as tropocollagen axis to form the triple helical structure known as collagen
  39. How are the subunits of collagen held together?
    • The subunits of collagen are held together or stabilized by inter and intra molecular bonds
    • The degree of cross-linking increases with the age of the animal
  40. What is elastin?
    In addition to proline and glycine, elastin has alanine and valine, which make the molecule more extensible
  41. What is the ratio of collagen to elastin?
  42. What allows desmosine to stretch?
    Allysyl and lysyl groups in desmosine enable cross linkage between elastin units to enable the molecule to stretch out or elongate
  43. Why are connective tissues important?
    Facilitate transmission of contractions/relaxations to bone and other tissues to permit motion
  44. What happens to homeostasis after the animal dies?
    Catabolic processes exceed the anabolic ones and the biochemical changes that are responsible for the conversion of muscle to meat upon slaughter of an animal
  45. What is the primary function of the muscle?
    To convert chemical energy into mechanical energy
  46. How is ATP production sustained in the live animal?
    ATP production is sustained by aerobic respiration when the animal dies, blood circulation stops and production of ATP declines
  47. What happens when ATP production from creatine-phosphate, ADP and Mb-O2 are exhausted?
    • The muscle falls on its glycogen reserves for ATP production
    • Production of lactic acid ensues, pH decline up to a final pH of about 5.5
  48. What is caused by the low pH in dead animal tissue?
    The low pH causes inactivation of glycolytic enzymes to stop further ATP production
  49. What causes the muscle fiber to stiffen or toughen post mortem?
    When ATP level falls, Ca2+ ions in the sarcoplasm cannot be pumped back from the sarcoplasm into the sarcoplasmic reticulum, the Ca2+ stay complexed with troponin and prevents bidning of tropomyosin with actin.  In the absence of the tropomyosin, actin binds to myosin on a moe extended period,  This causes muscle to stiffen or toughen and is known as RIGOR MORTIS
  50. How is rigor mortis resolved?
    Cathepsins, but mostly caplains break down the crosslinkages in the actin complex to resolve rigor
  51. Describe the condition of PSE meat
    • PSE = Pale, soft, exudative meat
    • It is characterized by an abnormal color, consistency, and water holding capacity, making the meat dry and unattractive to consumers.
    • Normally, calcium ions are used by the body to activate muscles, composed of myofibril cells. Ca2+ is transported out of the sarcoplasmic reticulumsurrounding muscle fiber cells, and leads to metabolism and contractions of the myofibers. Under PSE conditions, twice the amount of Ca2+ is released post-mortem, which causes excessive muscle glycolysis, and the buildup of lactic acid. This lactate accumulates in the postmortem muscle, and leads to a very low pH.
    • As the pH drops, proteins in the myofibers are denatured, leading to abnormal cell structure and function. The result is a pale tissue color, and a soft, almost mushy texture. The muscle cells shrink, and less water is held within the cell membrane. Subsequently, the myofibers will continue to lose water content as the meat is cooled and stored, leading to excessive drip loss.
Card Set
Food Comm- Red Meats
Food Commodities Red Meats