Muscle Tissue. Muscle Tissue (skeletal muscle) Some soluble proteins Connective Tissue Adipose Tissue (fat)

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1 Muscle Tissue (skeletal muscle) Some soluble proteins Connective Tissue Adipose Tissue (fat) Between muscles, it is called seam fat (usually trimmed) Within the muscles, it is called marbling (often prized) Muscle Tissue Muscle is made up of bundles of muscle fibers Muscle fibers contain thousands of myofibrils Myofibrils contain thousands of thin and thick filaments of actin, myosin and other proteins. The color of meat depends largely on myoglobin (with some contribution from mitochondria) Sarcoplasm proteins Enzymes Mitochondrial & Nucleoproteins Lysosomal Proteases Myoglobin Connective Tissue Collagen Elastin Reticulin Titin Nebulin Vinmentin Synemin Myofibrillar Proteins Myosin -actin Tropomyosin Troponin -actinin M-Protein C-Protein Myomesin A Ferroheme protein that binds O 2 C H 3 C H C H 2 C H 3 N N N Fe N H 2 C C H 2 C O OH C H O 2 C H 3 C C H 2 HO C H 3 C H C H 2

2 Myoglobin (FeII) is Purple Oxymyoglobin is Red Metmyoglobin (FeIII) is Brown Myoglobin is oxidized to metmyoglobin at low partial pressure of O 2 A steak can be purple or brown underneath, where O 2 is limited. Total Protein (%) P [O 2 ] (mm Hg) Collagen Triple helices of proline-rich peptides Covalently crosslinked Assembled into fibers Electron Micrograph of Fiber Globular Heads a-helical coiled-coil rod Helical Coiled coil LC Hinge region S1 LC

3 Myosin Domains rod S1 hinge light meromyosin (LMM) S2 Assembled Dimers salt bridge charged residues hyd core charged residues Actin salt bridge Actin Tropomycin Troponin Ca ++ Ca++ Ca ++

4 thick filaments thin filaments Release of acetylcholine at the myoneural junction causes the SR to release Ca + +. Ca ++ ion causes troponin and tropomyosin to move aside to expose binding sites for myosin Myosin heads bind actin fibers ONLY if he myosin does not have ATP bound at its binding site (ADP is OK) The Actin-Myosin-ADP-Pi complex, the myosin head is in the 90 conformation. The ADP-Pi dissociates, causing the head to flex to the 45 form, and the actin moves along the myosin ATP binds to myosin and causes the actin-myosin complex to dissociate The ATP form of myosin relaxes to the 90 conformation

5 Meanwhile - at the myoneural junction Acetycholinesterase disposes of acetylcholine The sarcoplasmic reticulum pumps the Ca ++ back inside (using ATP to do it) And the system is ready for another power stroke cycle Unless Bloodflow, O 2 transport stop But enzymes keep working, anaerobic metabolism makes ATP and lactic acid. Eventually, that stops, too, and ATP is depleted. Leaving tissue flooded with Ca ++ and without ATP to cause AM dissociation. Rigor Ca ++ diffuses away ADP breaks down or binding site is disrupted Protein-protein interactions break down and the sarcomere is disrupted (loss of Z- line) Stretching produces more tender meat Endogenous proteases continue softening the meat 1. High water binding activity 2. Increased tenderness 1. Reduced water binding activity 2. Increased toughness from myofillament overlap

6 high ph meat dark color ph >6.5 high water binding capacity very firm texture intermediate ph meat ph 5.8 bright color moderate water binding capacity slightly firm texture low ph meat pale color ph <5.5 low water binding capacity soft spongy texture 1. Net charge effect 2. Steric effect myofilaments Binding in chopped meat products ph-dependent water binding capacity Excellent emulsification properties - if solublized + 3% NaCl muscle chunk Binding in chopped meat products Binding in chopped meat products extracted salt soluble protein Heat-denatured protein muscle chunk solid meat product

7 Effect of ph on myosin solubility in 0.6 M NaCl Effect of heat on myosin solubility and gel formation 20 % Soluble % Soluble in 0.6 M NaCl 15 Gel Rigidity (x10 2 dyne/cm 2 ) ph adapted from Samejima et al., Temperature ( C) adapted from Samejima et al., Temperature ( C) Fish (Muscle) Proteins Fish (Muscle) Proteins Lean fish muscle contains % protein (~80% moisture) Of this protein: 20-30% is water-soluble sarcoplasmic protein 70-80% structural protein, soluble at high ionic strength (i.e., just like beef muscle), and 2-3% connective tissue Not very different from other animal muscle proteins Fish Spoilage Caused by bacterial proteases & other enzymes Pseudomonas putrefaciens & other Ps. spp. + Alteromonas spp. Make from which causes odor H 2 S Cysteine rotten egg (CH 3 ) 2 )S Methionine cabbage Acetic, butyric Gly, Ser & Leu fruity (CH 3 ) 3 )N TMAO* fishy/ammonia burnt rubber (CH 3 ) 2 )NH TMAO fishy/ammonia NH 3 Amino acids ammonia Scombroid Poisoning Unusual problem with Fish Proteins Bacterial spoilage in two stages Bacterial proteases: proteins amino acids His decarboxylase: Histidine Histamine + CO 2 Histamine signals a (bogus) immune response: Rash, diarrhea, flushing of the face, sweating, headache, dizziness, and vomiting. Organisms include (example spp.): Hafnia alvei Lactobacillus 30a Klebsiella pneumoniae Enterobacter aerogenes Escherichia coli Proteus morganii Clostridium perfringens (all but one, Plp enzymes) * osmolyte