Food chem 13
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What is muscle made up of?
Muscle fiber bundles held together by connective tissue (collagen) and anchored by tendons (collagen)
What does each fiber bundle of muscle look like?
Each fiber bundle contains many long muscle cells (called muscle fibers) which can be seen by the naked eye
What is a sarcolemma?
Each muscle cell has a cell membrane or cell wall termed the sarcolemma
What does a single muscle fiber look like under a polarized light
If we look at a single muscle fiber (cell) under a polarized light microscope, it contains striated structures termed sarcomeres
What are sarcomeres?
The sarcomeres are patterns produced by structural entities, ermed myofibrils, within the cell cytoplasm (sarcomplasm)
What are myofibrils composed of?
Myofibrils within the cell are composed of overlapping myofilaments which result in regions of dark and light striations (sarcomeres) when viewed under plane polarized light
What are 'A' bands?
the dark bands of the myofibrils sen under plane polarized light are termed 'A' bands (for anisotropic- not capable of rotating plane polarized light)
Whst are 'I' bands?
Light regions of the myofibrils are called 'I' bands (for isotropic- capable of rotating plane polarized light)
What is the myofilament made up of?
The myofilament itself is made up of two groupnigs of conctractiled proteins termed actin and myosin
What does the cental myosin bundle consist of?
The central myosin bundle consists of ~400 individual myosin molecules arranged in a staggered fashion
What is the general construction of a myosin unit?
Each myosin unit is a double alpha helix terminating in a globular head having ATPase activity
What is actin?
Actin is really a double helix of 'F' actin of 'Fibrous' actin, which is a polymerized form of 'G' or globular actin
What happens in the presence of ATP in muscles?
In the presence of ATP- G actin instantly polymerizxes into F actin, causin a shortening or contraction in the muscular fiber
What controls the polymerization and depolymerization of actin?
The ATPase of myosin controls the polymerization and depolymerization of actin to provide muscle contraction initiated and controlled by nerve impulses
What are sarcoplasmic proteins?
- Albumins (soluble in water) and globulins (soluble in dilute salte solutions)
- These also include enzymes as well as myoglobin which carries )2 in and out of muscle tissue and provides it with its red color
How is actomyosin formed?
- The contractile proteins- actina nd myosin- can be extracted from homogenized muscle tissue using high ionic strength salt solutions and then purified by crystallization
- When these purified proteins are mixed together in vitro, a complex called actomyosin is formed
How does the dissociation of actomyosin take place?
The dissociation of actomyosin takes place if ATP is present and association takes place in the presence of ADP and Mg++ ions
What is rigor mortis?
- This in vivo reaction is associated with a strong and irreversible interaction of myosin and actin due to the lack of ATP, much like the behavior of the in vitro actomyosin complex
- With death- blood circulation stops and the aerobic TCA cycle ceases to functio as there is no oxygen available via respiration and ATP becomes limited
- Anaerobic glycolysis takes over- this alternate metabolic pathway using glycogen continues and tries to compensate for ATP lost, but can only do so at ~10% of the rate of the TCA cycle, hence a gradual loss of ATP from the system occurs, with lactic acid building up and pH of the muscle drops
- At a critical minimum ATP level, actin and myosin associate to form an actomyosin complex, which makes the muscle inextensible and rigor occurs
Why do we 'age' beef?
Given time (aging) rigor generally resolves itself and this is one of the reason why we age beef
What happens during the aging of beef?
- With aging there is breakdown of the myofibrillar proteins by endogenous proteolytic 'Catheptic' enzymes
- These break some of the bons in myosin or actin, effectively breaking down the actomyosin complex over time
What is connective tissue made up of?
What is collagen used for?
Collagen is of commercial importance, because it is used to make gelatin- a protein with excellent gelling and water binding properties
What is the fundamental collagen unit?
The fundamental collagen unit is a triple suprahellix, caled tropocollagen
What is the toughening of meat with age of the animal associated with?
Toughening of meat with age of the animal is considered due to ovalent bonds developing between tropocollagen molecules over time
How is gelatin produced?
- Hide, bones and meat discards are placed in water and heated in a retort under pressure
- Around 80° the collagen matrix begins to disintegrate and solubilize due to the breaking of intermolecular hydrogen bonds
- Fast is skimmed- the final calrified product is a viscous solution which will gel if allowed to cool- it is drum dried and ground to form a gelatin powder
How is gelatin hydrated?
Gelatin is hydrated in the presence of water and high temperatures
What happens when gelatin is hydrolyzed?
It forms a three dimensional thermo-reversible gel via predominantly hydrogen bonding of the protein polymers which entrap water or can be made into a rigid film when water evaporates (edible capsules)
Why do fish have less connective tissue than animals?
Fish muscle has much less connective tissue as fish require less support in its natural environment- thus does not hold together as well during cooking or processing
What is a common problem in slow frozen fish products and why?
Proteins are more easily denatured with a corresponding loss of water holding capacity- a common problem in slow frozen products (ice crystal tissue disruption)
How is surimi made?
- Tissue is first ground and washed with water to remove the water soluble sarcoplasmic proteins while retaining the contaractile myofibrillar proteins (actin/myosin)
- The residual actin/myosin protein paste is then stabilized with a crygoenic stailizer (commonly sugar alcohol)
- Products are formed into crab and scallop analogs to resemble an indentifiable product - appropriate flavor is added
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