Basic composition of meat: characteristics of protein and fat in muscles in common slaughter animals Flashcards
1
Q
Protein
A
- most important muscle constituent
- digestibility:
- meat protein = 95%
- plant protein = 85%
- 3 groups:
- myofibrillar proteins —> nutritional
- sarcoplasmic proteins —> colour of meat (red)
- connective tissue proteins or stromal proteins —> structural
2
Q
- Myofibrillar proteins:
A
- most important
- insoluble in water but soluble in saline solution —> important for the manufacturing of certain
meat products - salt must be added for tenderness, if not enough salt —> protein is not released —> meat is
hard - composed of:
- contractile proteins:
- myosin —> thick filament, 50-60% - actin —> thin filament, 20%
- regulatory proteins: troponin and tropomyosin (7%)
- cytoskeletal proteins: titin, actinin, nebulin, desmin, systemin, other structural proteins (23%)
3
Q
- Sarcoplasmic proteins:
A
- water soluble
- soft protein structure containing most of the red muscle pigment myoglobin
- composed of:
- creatine kinase
- myoglobin and hemoglobin = the two main pigments, most important - various proteases
4
Q
- major chemical forms of myoglobin:
A
- deoxymyoglobin: ferrous (Fe2+) heme iron, low O2, associated with vacuum packaging =
purplish-red/purplish-pink colour - oxymyoglobin: unstable, ferrous heme iron, cut meat exposed to O2 = bright cherry red colour
—> as exposure increases, oxymyoglobin penetrates deeper - metymyoglobin: oxidation of ferrous to ferric (Fe3+), low O2 required = brown colour —>
surface discolouration
5
Q
- Stromal proteins:
A
= connective tissue surrounding the fibres and unites them in bundles
- intramuscular connective tissue (IMCT) consist of 3 main structural components:
- endomysium = layer of thin connective tissue separating individual muscle fibres (contraction- relaxation)
- perimysium = 90% of all IMCT, a layer of connective tissue that separates individual muscle fascicle in each muscle
- epimysium =a binding of connective tissue defining and separating individual muscles
6
Q
• collagen:
A
- dissolves to gelatine in hot water, white in colour
- most abundant protein in animal body (20-25% of total body protein): bone, tendon,
ligaments, cartilage, skin - to transmit force and hold things together —> tough and inert
- content varies according to muscle function and toughness increases with age (increased
cross-linking) - positive function = binds water —> responsible for juiciness of meat
- negative function:
- high cross linkage (older animals) —> difficult culinary preparation as meat becomes tough
- has little binding ability —> not very valuable in processed meat
- heating of collagen:
- if heated with moisture —> will shrink
- of heated when dry —> become very hard and impermeable —> important when
handling collagen and/or natural casings - highly resistant to enzymes —> enzyme tenderisers are ineffective
- amino acids:
- = glycine, proline, hydroxyproline
- contain large amount of hydroxyproline which is lacking in other proteins —> commonly
measured to determine collagen content
7
Q
• elastin:
A
- binds muscles together
- tough and yellow in colour
- doesn’t break down during cooking, needs to be cut away from the meat
8
Q
• keratin:
A
horn, hoof, hair, feathers
9
Q
Determination of protein content
- by Kjeldahl’s method
A
- nitrogen estimation using neutralised HCl —> use 6,25 coefficient to calculate from the nitrogen protein content —> muscle contains about 16% of nitrogen
- 3 steps: digestion, neutralisation and distillation, titration
10
Q
Fat deposits in animal body
A
- subcutaneous: 60-70%
- surrounding organs: e.g. kidney 5%
- intermuscular: 20-35%
- intramuscular fat:
- between muscle fibre bundles
- lead in higher accumulations in marbling —> contributes to tenderness and flavour of meat
—> ideal for steaks and roasted meat dishes
11
Q
Fatty acids
- different content depending on species and type of muscle
- saturated fatty acid:
A
- palmitic acid —> second most abundant fatty acid in meat lipid content
- stearic acid —> third most abundant fatty acid in meat lipid content
12
Q
Fatty acids
- different content depending on species and type of muscle
- unsaturated fatty acid:
A
- oleic acid:
- most abundant fatty acid in meat lipid content - pigs have higher amounts than cattle or sheep
- linolenic acid
- higher in soft fat: chicken > pork > beef
13
Q
- polyunsaturated fatty acid:
A
- eicosapentanoic acid, decapapentaenoic acid
- omega 3 and omega 6 = essential polyunsaturated fatty acids
14
Q
Determination of fat content
A
- by Soxhlet method
- weight comparing before and after the evaporation of organic solvent
- estimate water content % before the procedure —> xylene through the sample —> fat is
extracted —> calculate results - varies depending on the type of meat between 3-10%
15
Q
Water
- inversely related to fat content
- total water is divided into:
- bound H2O:
A
- smallest compartment of water, 1-2%
- strongest of the three
- tightly associated with meat proteins —> nearly impossible to remove from meat
