2. Chemical composition and structure of meat

Basic composition of animals

• 55-60% water

• 3-4% minerals

• 35-40% organic substance: Carbon, hydrogen, oxygen, nitrogen, sulphur, other elements

Three groups of important organic compounds found in animals

1. Protein

2. Fats

3. Carbohydrates

proportion can vary greatly

What does muscle tissue consist of

• ~75% water

• ~20% protein

• ~5% remaining:

  • Fat

  • Small amount CHO (mainly glycogen)

  • Free amino acids (AA), dipeptides and nucleotides

What does the protein in animals consist of?

• 2% stromal protein:

  • Connective tissue proteins

  • Collagen

  • Elastin

  • Soluble in alkaline or acid solutions

• 5.5% Sarcoplasmic protein

  • Enzymes

  • Myoglobin

  • Water soluble

• 11.5% myofibrillar protein

  • Actin

  • Myosin

  • Nebulin

  • Tropomyosin

  • Soluble in salt solutions

Proteins

• Are composed of amino acid chains (20 common AA)

• Animals cannot synthesize amino group -NH2 (characterises AA), must have protein in diet.

• Per protein source → many AA synthesized by animals

Essential Amino Acids

• Are vital for some animals but not for others/depends on stage of life

• E.g.: Proline is essential for chicks but not adult broiler birds

• Lysine: essential for pigs

How are two amino acids linked

• They are reduced and linked by an S-S bond: cystine produced

How are small proteins held together

• Held by H bonds and various other mechanisms

• H bonds form between N of amino group and O of carboxyl group of different AA

• Chains of more than 50 amino acids are considered proteins

Denaturation of proteins

• Denaturation leads to loss of solubility in aqueous solution and loss of enzymatic, immunological/hormonal properties

• This affect structure and characteristics of meat.

Collagen

• Is a stromal protein

• One of the most common proteins in the body → major component in connective tissue

• Various types

• Different connective tissue sheaths in muscle composed of different collagens

What are the three types of connective tissue sheaths, what do they surround and what collagen type is found there?

Where are the different types of collagen found?

Collagen fibres

• = multiple collagens together

• One collagen = tropocollagen triple helix = three polypeptide chains twisted together into coiled triple helix

• Multiple collagen = Fibril

• Over time within the fibril the tropocollagens form links

• this makes the skin tougher = longer cooking times

Collagen strength

• At the amino group end of non-helical part of tropocollagen molecule - intermolecular cross links formed

• Collagen in tendons is more cross-linked than in cartilage from organs (like ear/nose)

  • Cross-linking is more resistant to tensile strength

• As animals get older → collagen cross-links stabilize and diameter of fibril increases

Effect of cooking on cross-links in collagen

• After cooking cross-links weaken but do not break → toughness of older animals (collagen more heat stable and less soluble)

• Cooking collagen from younger animals produces gelatin is soft and soluble → forms gel on cooling

Role of carnosine in animals

• Found in all species

• Consists of B-alanine and histidine

• Buffers to prevent large acidity changes

• Maintain muscle pH in physiological range 6.8-7.4

Role of anserine in animals

• Found in all species, but especially in muscles of birds

• Consists of B-alanine and 1-methylhistidine

• Works as buffer to keep pH between 6.8 and 7.4

Role of balenine in animals

• Mainly found in muscles of pigs and baleen whales

• Dipeptides consisting of b-alanine and methylhistidine

• Buffers to maintain muscle pH between 6.8 and 7.4

Lipids vs Fats

Feature	Lipids	Fats
Composition	Fats, phospholipids, steroids, waxes, etc	Glycerol molecule with three fatty acids
Primary function	Diverse	Energy storage
Solubility	Generally insoluble, some are amphipathic	Highly insoluble
Health	Varies	Saturated and trans fats can increase heart disease risk, unsaturated can be beneficial

What is fat made up of?

• Of molecules called triglycerides

• Essential parts of cell membranes and energy storage

• Basis of steroid hormones

• Contain principally C, H and O

• Triglyceride = three fatty acids linked to glycerol

Linoleic and linolenic acid

Linoleic acid consists of 18 carbons with two double bonds

Linolenic acid consists of 18 carbons with three double bonds

How fat composition can be changed in animals?

• Feeding a monogastric animal such as pigs or chickens a different diets will change the fatty acid composition of meat

• Easier in monogastric species because in ruminants like lamb, beef and sheep, the unsaturated fatty acids can be turned into saturated ones during digestion.

• Maize based feed gives a higher unsaturated fatty acid content, while lamb has a lower unsaturated content

Desirable intake of omega 6 and omega 3

• Ideally a ratio of 4:1/5:1 (n-6 to n-3) is desirable

• Western diets often have higher ratios

• Proportion is important → incidences of cardiovascular disease

• n-3 reduces blood clotting and n-6 counteracts this effect

Why are omega-3 and omega-6 important?

• Omega-3 is linolenic acid and is turned into EPA and DHA acids

  • Linolenic acid is mostly found in linseed oil.

• Omega-6 is linoleic acid and is turned into arachidonic acid

  • Plant oil are generally rich in linoleic acid and less in linolenic acid.

How does the composition of fatty acids affect characteristics of triglycerides

• Melting points

• Potential for oxidation

• Nutritional value (to some degree)

TG composition and softness

• Mainly saturated FA → solid at room temp

• Unsaturated FA → usually liquid at room temp

Why can meats with unsaturated fats not be produced as much?

Because of oxidation

Which meats are most prone to off-flavors in uncooked meat?

• Fish (most prone) > chicken > red meat (lamb>beef>pork)

• Pork is less prone than beef because it has lower myoglobin which catalyzes the oxidation reaction