P4. Meat - Muscle contraction Flashcards
Red meat generally refers to?
- encompasses 6 types of meat
- refers to mammalian skeletal muscle tissue consumed as food
- encompasses beef/veal, buffalo, mutton/lamb, goat, pork and horse (NO POULTRY)
most of the meat consumed is from ________ animals. why?
- young animals
- bc strengthening of muscles with time leads to tougher meat
why is color of fresh meat red to reddish pink?
owing to large concentration of myoglobin (oxygen storage protein) present in muscle
what other tissues/components may also be present in red meat? (5)
- bone
- connective tissue
- adipose tissue
- nerves
- blood
factors that affect gross composition of red meat (6 + 3 ish)
- species
- breed
- age
- sex
- nutrition of live animal
- muscle condition in live animal (related to level of activity)
- anatomical location of retail cut
- extent of trim (fat)
- methods of processing/cooking
composition of lean tissue for meat (5)
- water (around 70-74%)
- protein (around 20-21%)
- lipid (around 5-6%)
- ash (1%)
- carbs, vitamins, other soluble organic constituents (1% of skeletal muscle)
water accounts for >___% of lean tissue by weight
- water is either ________ (to what? or ______ (trapped within what?)
- _______ water serves as what? when?
- > 70%
- bound (to proteins)
free (trapped with muscle cells) - free water serves as medium in which nutrients and other solutes are dissolved and transported
- when animal is alive
how is protein content typically derived in proximate analysis of meat?
- percent of ______ is multiplied by ______ –> bc?
- from determination of muscle nitrogen content by Kjeldahl analysis
- percent of nitrogen multiplied by 6.25 –> based on average nitrogen content of protein (16%)
is the proximate analysis of protein in meat accurate?
- as much as 10% of muscle N originates from non-protein sources (ie nucleic acids and free aa)
- thus, true protein content of red meat is somewhat lower than usually reported (19% vs 21%)
lipids can account for __-___% of fresh weight of separable lean tissue
- minimal values (___-___%) represent what? present in all living cells?
- larger values indicate what?
- 1-13% of fresh weight
- 0.5-1% represent membrane phospholipids
- presence of variable amounts of neutral storage lipids which are primarily TG
what does ash refer to when analyzing meat content? (2)
- refers fo inorganic residues, remaining after muscle sample is incinerated at extremely high temps
- represents mineral component of muscle (Ca, Mg, Fe)
main carb in muscle?
vs main carb in meat? why?
- glycogen (short term energy storage)
- lactate bc during conversion of muscle to meat, glycogen is largely converted to lactate by anaerobic glycolysis (by bacteria and microorgs and enzymes that are in the “dead” body)
why is red meat an excellent source of protein in human diet?
because dietarty requirements for essential aa reflect the considerable skeletal muscle content of our own bodies
proteins in skeletal muscle can be separated, based on their _____A_____ into 3 classes:
- what?
- percent of total muscle protein?
- _____A_____?
- solubility
1. sarcoplasmic: 30%, soluble (float in cytoplasm)
2. myofibrillar: 50-60%: soluble in concentrated salt solutions (0.3M NaCl) –> otherwise, they precipitate
3. Stromal: 10-20%, insoluble –> attaches muscle tissue to bone
sarcoplasmic proteins are dissolved in what?
cytoplasm/sarcoplasm inside muscle cell
sarcoplasmic proteins
- 2 ex
- involved in (2)
- colors of fresh, cooked and cured meat products are due to ?
- myoglobin and glycolytic enzymes
- regulation of cell and energy homeostasis
- due in large part to myoglobin content and oxidation state of iron in the heme group associated with myoglobin (Fe2+ = red, Fe3+ = brown)
why is veal a paler color compared to adult beef?
- because myoglobin content tends to be in lower abundance in young animals
- not old enough to have produced a lot of myoglobin
myoglobin has primarily ______ structures
- contains a ________ ring which contains _______
- helical
- porphyrin ring
- contains a heme
myofibrillar proteins:
in muscle tissues, where salt concentration is ______ (above or below their solubility?), myofibrillar proteins are assembled into what?
- role?
- 0.15M (below solubility of 0.3M)
- into complex quaternary structural filaments
- regulate, support or perform mechanical work of contraction
which proteins (2) account for ___ of total protein in skeletal muscle (for mechanical work)
- myosin and actin (contractile proteins)
- 65% of total protein
what regulates myosin and actin activity? (2)
troponin complex and tropomyosin
what is included in myofibrillar protein (6)
- myosin
- actin
- troponin complex (C, I and T)
- tropomyosin
- titin
- nebulin
behavior of myofibrillar proteins is important in fresh meats bc ?
because extent of contraction and rigor mortis development are critical in successful conversion of muscle to meat, as well as in processed meats
what is rigor mortis? can eat?
when muscle becomes very stiff after death (animal can’t make ATP anymore) –> can’t eat it –> need to wait for it to resolve before eating
what do stromal proteins form?
- these ________ proteins contribute to what?
- fibrous connective tissues that strengthen and protect muscles
- insoluble
- meat toughness
what is the most prevalent of stromal proteins?
- this protein is also the most what?
- collagen!
- also the most abundant protein in animal body
although collagen makes only a small/big contribution to total skeletal muscle protein, importance of collagen is highlighted by the fact that ?
- small
- processing and cooking methods for meat are designed to disrupt and partially solubilize collagen fibers (hydrolyze = more tender)
3 sources of non-protein nitrogen in skeletal muscle?
- creatine
- amino acids
- nucleic acids and nucleotides
total content of non-protein N only accounts for ___% of net weight of muscle
- however, which 2 sources are key components in what?
1.6%
- creatine and nucleotide ATP are key components in development of rigor mortis
skeletal muscles consist of a ________ arrangement of what?
- parallel
- of elongated multinucleated cells called myofibers (muscle fibers)
individual myofibers range from ___ to ____ um in width and from what to what in length? sometimes spanning what?
- 10-100 um in width
- few mm to several cm in length
- sometimes spanning entire length of muscle
hierarchical structure of skeletal muscle? (3 layers)
- each myofiber is encase in layer of connective tissue called endomysium
- groups of myofibers are organized into primary and secondary bundles (fascicles) that are segregated by another layer of connective tissue called perimysium (surrounds muscle bundle)
- final layer of heavy connective tissue sheaths, called epimysium surrounds the whole muscle –> those sheaths merge with connective tissue tendons to link muscles to bones