Chemical composition and structure of meat
19 important questions on Chemical composition and structure of meat
In view of its complexity, an animals body consists of relatively few kinds of chemical substances
- 55-60% water
- 3-4% minerals
- water + minerals = inorganic substances
- 35-40% organic substances
- carbon (C)
- Hydrogen (H)
- Oxygen (O)
- Nitrogen (N)
- Sulphur (S)
- Other elements
What are the three groups of organic compounds?
- Proteins
- Fats
- Carbohydrates (CHO)
Muscle tissue
- 75% water
- 20% protein
- 5%
- fat
- small amount CHO (mainly glycogen)
- free amino acids (AA), dipeptides & nucleotides
Name the three groups of meat proteins & provide an example of a protein for each group
- Myofibrillar proteins (11.5%)
- actin
- myosin
- nubulin
- tropomyosin
- Sarcoplasmic proteins (5.5%)
- myoglobin
- connective tissue proteins (2%)
- collagen
- elastin
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Name the different functions of proteins in meat
- Contractile --> actin & myosin
- Transport function --> haemoglobin & myoglobin
- Structural --> collagen
- Enzymes catalysing chemical reactions --> creatine kinase
- Hormones --> insulin
- Antibodies involved in immunological responses
- Osmotic functions --> blood plasma albumin
How is cystine produced? And where is it important for?
Disulfide bonds between cysteine molecules important for overall structure of proteins
What are the various types of collagen?
- epimysium
- whole muscle
- Type I
- perimysium
- fibre bundles
- Type I & III
- endomysium
- fibres
- Type IV & V
What are the 3 main peptides that occur in small, but varying amounts in the meat?
- Carnosine & anserine found in all species
- Anserine especially in muscles of birds
- Balenine in muscles of pigs & baleen whales
Carnosine - histidine
Anserine - 1-methylhistidine
Balenine - 3-methylhistidine
What are the important fatty acids in meat?
- Oleic, plastic & stearic acids = some of most common naturally occurring FAs
Three FAs that are not synthesised by mammals (--> essential FAs)
- Linoleic acid
- Linolenic acid
- Arachidonic acid
obtained form diet
Difference between linolenic and linoleic acid
Linoleic acid used by animal to synthesis arachidonic acid
What is conjugated linoleic acid (CLA)
- Mixture of geometrical / positional isomers of linoleic acid with two conjugated double bonds
- CLA thought to have health benefits (anti-cancer, -inflammatory)
- Most dietary CLA from ruminant fats consumed as meat / milk - levels are quite low
- CLA formed by luminal microorganisms from linoleic & vaccenic acids
Two types of cholesterol transported in blood in lipoprotein particles
- Very low-density lipoproteins (VLDLs)
- transport lipids, including cholesterol, to tissues of body
- high levels = atherosclerosis
- High-density lipoproteins (HDLs)
- remove cholesterol from tissues
Explain how lipid oxidation occurs & how it affects meat quality
- Unsaturated FAs prone to oxidation
- Meat in which most fat are saturated cell membrane that contain phospholipids
- PUFAs in phospholipids form FA hydroperoxides
- FA hydroperoxides are unstable and produce off-flavours
- Process is rapid (1-2 days)
- Leads to stale, rancid flavour = "warmed over flavour"
- Fish > chicken > red meats (pork<beef<lamb)
- errors iron of harm pigment catalyses oxidation
- Three stages: initiation >> propagation >> termination
- initiation catalysed by various factors
- light, heat, metal ions, iron-containing ham pigments
- Also promoted by NaCl
What are the two main classes of carbohydrates
- include monossacharides (dextrose) & dissacharides (sucrose)
- include glycogen - polymer of glucose
CHO composed of C, H, O
Name the different types of fat deposits in meat & explain why certain deposits might be more valuable than others
- Subcutaneous = under skin (easily removed)
- Intermuscular = between individual muscles
- Intramuscular = within muscle (marbling)
more intermuscular --> more juicier meat + more flavour
The most important muscle of poultry is the breast muscle, what is the Latin name for it
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What are red and what are white fibres (& intermediate fibres)
- oxidative fibres --> contain fat droplets
- relativeer weak ATP-ase & phosphorylase activity
- stond aero
bic enzyme activity - cytochrome oxidase & succinct dehydrogenase
- slow twitch --> postural muscles
White fibres
- glycolytic fibres --> high glycogen content
- strong ATP-ase & phosphorylase activity
- ATP-ase hydrolyse ATP; phosphorylases citaat - initial stages glycogen breakdown
- weak aerobic enzymes
- fast twitch --> muscle main role is rapid but intermittent movement
intermediat fibres
- tend to have strong ATP-ase & glycolytic enzyme activity
- variable activity of enzymes of aerobic metabolism
Sliding filament hypothesis
Explain the role that ATP plays in the muscle contraction
- Both actin & myosin bind ATP
- Each lobe of myosin can bind an ATP molecule
- Each globular actin molecule can also bind a molecule ATP
- Polymerisation of actin into chains --> ATP hydrolysed to ADP
- Myosin molecule acts as ATP-ase - activity enhanced greatly by presence actin
- Hydrolysis of ATP by actomyosin ATP-ase = mechanism by which contraction is fuelled
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