Fibrous Connective Tissue sh
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COLLAGEN • Main structural protein of CT Characteristics: • Most abundant protein in body (20%) • Many types formed (11 – 12) o 5 found in muscle • Relatively inelastic (doesn’t stretch well) • Colour: individual fibers are clear o Sheath or tendons appear white o Vs elastin – yellow in colour • Protection • Strong – important in structural & functional roles o The # of fibrils in a fiber is dependent on load & stress factors for the collagen fiber o The # of fibers present is dependent on tissue load (muscle’s specific role) o Muscles involved w locomotion have high amounts of collagen o Strength & toughness increased by: § Two types of crosslinks give collagen high tensile strength: • Intramolecular crosslinks between theα chains (PP strands) within tropocollagen molecules • Intermolecular crosslinks between adjacent tropocollagen molecules • Tropocollagen – the molecules that make up collagen Found in: • Tendons – connect muscle to bone • Ligaments – connect bone to bone • Bones • Cartilage • Muscle • Skin – high amounts of collagen • Blood vessels Industrial uses: • Leather, glue, cosmetics, food processing o Leather – collagen is responsible for strength Structural: Roles in muscle • Form and shape (integrity of muscle) o Holds muscle fibers together o Protects muscle fibers from being damaged from strong muscle contractions • Supports blood vessels & nerves • Contractile force generation and transmission Meat quality: • Responsible for background toughness of meat (“grissle”) • Large amounts of insoluble collagen decreases meat tenderness • Collagen cannot be broken down by calpain in PM aging Location of Collagen in Muscle: • Sheets or cables visible to the naked eye • Epimysium in muscle proper This study source was downloaded by 100000828262717 from CourseHero.com on 06-29-2021 07:26:39 GMT -05:00
https://www.coursehero.com/file/7994093/Connective-Tissue/
1 o Sheaths (thick layers) surrounding whole muscle Perimysium in fasiculi o Thick layers of connective surrounding fasiculi • Endomysium in myofiber o Microscopic strands surrounding myofiber Synthesis of Collagen – from Tropocollagen • Tropocollagen – also known as protofibril o A high molecular weight protein o Is the structural unit of collagen fibril o Synthesized in fibroblasts – cells that originate from mesoderm • Amino Acids: o Non essential amino acids are the building blocks of collagen § Glycine – occurring at ever 3rd spot • Glycine is the only amino acid small enough to fit inside the collagen triple helix – increases stability § Proline and Hydroxyproline – makes up 25 – 33% of total amino acids • Hydroxyproline is only found in connective tissue proteins (collagen and elastin) • Analysing hydroxyproline content -­‐ used to determine the amount of connective tissue in muscle, impact tenderness o More hydroxyproline present in younger animals than in old § Glutamic Acid § Alanine § Hydroxylysine o Amino acids are synthesized into 3 polypeptide strands § Strands are called α chains (19 types) § Strands arranged into triple helix • Increases stability • Once tropocollagen is synthesized: o Aligned in a ¼ stagger § Produces unique striations o Assembled into collagen fibrils => bound into collagen fibers § Fibers are laid down in a criss cross lattice Effect of Age on Collagen • Young animal – deposits muscle as it grows & turns over existing muscle o Synthesizes large amounts of collagen § Required for structure § Few crosslinks in this collagen • Instead: soluble (reducible) intermolecular crosslinks that can be broken down o Reducible allows for continual turnover as the animal grows – need to break down crosslinks to synthesize proteins & deposit new muscle • crosslinks are susceptible to heat (heat liable) o Importance in cooking meat o Have high amounts of soluble proteins & hydroxyproline o Collagen turnover § Has inverse relationship with collagen fibril diameter • Small fibril diameter = faster collagen turnover (young animal) • Large fibril diameter = slower collagen turnover (older animal) § Growing calf has ~ 10% turnover / day This study source was downloaded by 100000828262717 from CourseHero.com on 06-29-2021 07:26:39 GMT -05:00
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https://www.coursehero.com/file/7994093/Connective-Tissue/
Aging animal o Collagen synthesis decreases – turnover of collagen is less o Crosslinking increases – more stable § Reducible crosslinks converted to pyridinoline = collagen associated w older animals • Pyridinoline has non-­‐reducible crosslinks (not easily broken down) § Decrease in collagen solubility § Collagen gets stronger (benefits daily activities) § More heat stable • Results in less tender meat o Maturity assessment in grading system (meat quality) § Considers age related changes in the skeleton • Bone ossification – conversion of cartilage to bone o CT cannot be measured directly by graders § However, they do know that as an animal ages, cartilage is converted to bone and there is more insoluble CT Factors Affecting Collagen • Diet o Affects crosslink stability § High CHO, high fructose, low crude protein = decrease crosslink stability = more soluble • Preslaughter feed restrictions o Turnover in cattle increased by finishing diets (high energy diets) § Cereal grains and low amounts of protein • Cattle: calf weaned -­‐> growing diet -­‐> finishing diet • Pigs: piglets weaned -­‐> starter diet -­‐> growing diet -­‐> finishing diet • Chickens: starter -­‐> grower -­‐> finisher • Species o Pigs have more collagen then cattle o Cattle have a larger problem with tenderness § Because pigs have higher amounts of SOLUBLE collagen (hydroxyproline) § Quality rather than quantity • Gender o Barrows have higher amounts of collagen than gilts • Muscles: o Total collagen content is based on hydroxyproline (amino acid) analysis o Heat stable vs soluble crosslink o Histological distribution § Epimysium = whole muscle § Peri-­‐ = bundles of muscle fibers § Endo-­‐ = individual muscle fibers • Endo and peri-­‐ = correlated with toughness o In beef: forequarter has higher amounts of collagen than hindquarter o Variation in muscle: § Cuts: hind + loin vs round § Affects prices of muscles Belgian blue – produces little CT or adipose tissue Piedmontese – low numbers of fibroblasts – affects CT synthesis – results in very tender meat This study source was downloaded by 100000828262717 from CourseHero.com on 06-29-2021 07:26:39 GMT -05:00
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https://www.coursehero.com/file/7994093/Connective-Tissue/
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ELASTIN – Connective tissue protein Characteristics • Elastic – needed for structure and function (structures that need to have the ability to stretch), and in muscle (meat) o Easily stretched and returns to shape • Resistant to: o Acid, base and heat (cannot be broken down easily) § Differs from collagen which can be broken down by acid, base and heat o Digestive enzymes o Elastase (synthesized in human pancreas) § Importance: indicates that man was developed as being partially carnivorous § Disagreements in literature • Extremely insoluble o Due to amino acid makeup: nonpolar amino acids and desmosine Found in: • Arteries (need to be flexible) • Abdominal wall • Ligament nuchae – more yellow in colour • Lungs • Skin • Muscle/meat (small amounts of elastin) o Elastin as % of total connective tissue § Longissimus vs semitendinosus (eye of the round – tough muscle) slide 2, pg 17 § Longissimus has 5:1 ratio collagen:elastin Synthesis of Elastin • Made of tropoelastin molecules o Synthesized by fibroblasts (same cells that synthesize collagen) • Elastin composed of: o Glycine (also in collagen) o Desmosine + isodesmosine (not in collagen) § Links for the tropoelastin molecules o Hydroxyproline (also in collagen) Copper Deficiency – important for synthesis of AA’s unique & major arteries leaving the heart • Copper needed for the synthesis of desmosine o Substrate: lysine (essential/indispensable amino acid) § Differs from collagen which is made up of non essential/dispensable amino acids o Enzyme: lysyl oxidase o Cofactor: copper (trace mineral) • Copper deficiency can cause death as elastin is needed for integrity of aorta *Connective tissue also contains elastin
AMOUNTS OF CONNECTIVE TISSUE INFLUENCED BY: Functional Demands of Life (Locomotion vs support, etc) • CT provides muscle with structure • Muscles need to be protected during contraction Connective Tissue Strength • Muscles involved with locomotion contain the strongest connective tissues o Shoulder and round of beef animal, ham of pig, etc • Larger animals have stronger CT than smaller animals • Older animals have stronger CT than younger animals This study source was downloaded by 100000828262717 from CourseHero.com on 06-29-2021 07:26:39 GMT -05:00
https://www.coursehero.com/file/7994093/Connective-Tissue/
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Leg Muscles vs Muscles Around Backbone • Leg muscles o Require supporting and connecting tissues (structural support for muscles involved with locomotion) o Increased collagen and crosslinking § Locomotive muscles have more collagen and elastin • Longissimus, etc • Muscles around backbone o Longissimus – has a support role, CT amounts can vary o Psoas major (tenderloin muscle or fillet mingon) – little CT because it doesn’t do much from a functional basis § Often very tender (even in older cattle) KNOW THESE GENERAL MUSCLE DIFFERENCES Background Toughness – collagen and elastin • Age -­‐ Younger = less background toughness (lower amounts of stable collagen) • Growth Rate -­‐ Faster growth rate = less background toughness (faster turnover) • Aging, Hanging, or Conditioning Meat -­‐ no effect on background toughness (does not break down CT proteins) o Calpain enzymes do not break down collagen MUSCLE VARIATION IN TOTAL COLLAGEN Most Collagen: Infraspinatus > Rectus femoris > Triceps brachii > Biceps femoris > Pectoral > Superspinatus > Semitendinosus > Gluteus medius > Semimembranosus > Adductor > LD – loin > LD – rib > Psoas major (Least Collagen) sh
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While the sirloin, loin and rib may not have as much collagen as muscles in the chuck and round, the collagen content may still be high enough to impact consumer satisfaction for tenderness -­‐Blade tenderization used – tiny blades break CT -­‐Controversy – allow surface bacteria that would normally be destroyed through cooking, to penetrate into the meat IMPACT OF COOKING ON MEAT: -­‐ cooking causes contraction of the muscles Texture • Tender muscles get tougher the longer they are cooked o Crosslinking forms in muscle proteins which toughens the myofibril • Tough muscles get tender the longer they are cooked o Cooking processes decreases the strength of CT (even though crosslinking occurs) § Add water! • Contraction of muscle fibers o Myofibril become stronger as crosslinking of proteins increases o Sarcomere length: § Shorter SL = more crosslinking = tougher beef Dry vs Moist heating This study source was downloaded by 100000828262717 from CourseHero.com on 06-29-2021 07:26:39 GMT -05:00
https://www.coursehero.com/file/7994093/Connective-Tissue/
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Changes in Juiciness • Juiciness decreases as meat increases in doneness o Moisture losses due to evaporation and drip o Loss of moisture is effected by original WHC of the muscle § DFD has higher WHC § Pumped products (moisture enhanced) – solution of salt and phosphates are pumped into meat to enhance juiciness, tenderness and flavour • Called a seasoned product • Most pork is pumped • Some pumping is good, by if product is over pumped, it will shrink when cooked Cooking Increases Solubility of Collagen • Starts at 56 – 65 C (relatively low temp) o Acts on triple helix • Fibrils are shortened to 1/3 original length – called collagen shrinkage • Hydrate (add water) and hydrolyse (break down) collagen o Collagen becomes more soluble – converted to gelatin § Age of animal – mature collagen is more resistant to gelatinization • Crosslinks weaken but do not break • Moist heat tenderizes meat o Moist heat = adding water to pan o Water hydrates collagen o Very effective for cuts high in collagen § Locomotive muscles, old etc o Vs dry heat = grilling, bbqing, pan frying etc § Dry heat should not be used for muscles from chuck or round – these will remain tough • If moist heat does not improve tenderness, it is most likely due to presence of elastin o Elastin does not respond to preparation with moist heat Collagen and Tenderness • Affected by o Total amount of collagen o Degree of collagen crosslinking § Ratio of heat stable (insoluble) to heat labile (soluble) o Fiber diameter of perimysium and endomysium § Larger diameter = more heat stable and less soluble collagen § Tougher meat Tough Muscle Fibers • Characteristics: o Abundant collagen (endomysium) around fibers o Many interfiber connections o Heat stable crosslinks o Elastin • Enzymes o Papain § Applied before cooking § Activated with heat and denature proteins during cooking process This study source was downloaded by 100000828262717 from CourseHero.com on 06-29-2021 07:26:39 GMT -05:00
https://www.coursehero.com/file/7994093/Connective-Tissue/
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Methods to Assess Meat Tenderness • Instrumental o Warner Bratzler shear force § Machine is used to emulate human mastication of meat § Force required to cut across muscle fibers is measured • Low force = more tender • Sensory Panels o Trained, untrained, consumer o Disadvantage: Lengthy and expensive This study source was downloaded by 100000828262717 from CourseHero.com on 06-29-2021 07:26:39 GMT -05:00
https://www.coursehero.com/file/7994093/Connective-Tissue/
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