collagen presentation

8/13/2019 Collagen presentation

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COLLAGEN AND GELATIN

Chapter 14


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Collagen

A major component of connective tissue. It

contributes significantly to the toughness of

meat product. Collagen is abundant in tendons, skins and bones.

It comprises about 33% of the total proteins of

mammals

Part of collagen is soluble in netraul salt

solutions, part is soluble in acids, but part of

collagen remains insoluble.


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Collagen

Glycine comprises 33% of amino acids and is distributed

uniformely at every third position. The repetitive

occurrence does not include first 14 amino acids from N-

terminus and first 10 amino acids from C-terminus of

collagen molecule. These peptides are known as

telopeptides.

Colllagen contains also hydroxyproline (up to 10%) and

hydroxylysine. Hydroxyproline contribute to thestabilization of collagen. Collagen low in hydroxyproline

denature at lower temperature (fish collagen)


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Collagen

Collagenase is the only enzyme that can

hydrolyse native collagen.

Clostridia produce this enzyme

Noncollagenase proteases may only cleave

the collagen telopeptide sites.


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Collagen

Tropocollagen is a long cylindrical protein

fibre that consists of three polypeptide

chains wound around each other insuperhelical fashion.


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Collagen - structure


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Collagen structure

Polypetides in tropocollagen may be

crosslinked with covalent bonds. The

number of crosslinks increases withanimal age. Toughness of meat depends on

the extent of crosslinks.


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Collagen occurs in several

polymorphic forms

Collagen type I - has two identical polypeptide

chains. Found in skin, tendon and bones.

Collagen type III - has three identical polypetidechains. Found in muscle.

Collagen type IV - consist of polypetide chains of

dissimilar size.

Collagen type V - composition is not very clear


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Collagen

Collagen can shrink to less than 33% of their original

length at the temperature referred to as shrinkage

temperature. This temperature is characteristic of

species from which the collagen is derived. The

shrinkage involves the collapse of tripple helical

structure.

The midpoint of collagen-to gelatin transition is defined

as the melting temperature. Transition of collagen togelatin involves breaking down both noncovalent bonds

as well as some covalent bonds (Shiff bases and alsol

condensation bonds).


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Processing of collagen to gelatin

involves:

Removal of non-collagenous material by

acid or alkali

Conversion of collagen to gelatin by

heating in the presence of water

Refining and Drying gelatin


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Gelatin

Moisture 9-12%

Ash 2%

Gelatin lacks tryptophan and is deficient in

sulfur containing amino acids


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Gelatin may be used as:

Gelling agent

Stabilizer

Emulsifier Thickener

Foaming agent

Water binder

Crystal growth modifier

Glaze

Adhesive


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Stiffness of gelatin gel depends

on:

concentration of gelatin

acidity

sugar

physical interference

temperaturepresence of enzymes


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GEL TINSFactors Influencing Gel Formation Concentration 1-2%

Temperature Cool Avoid Freezing Sugar Delays Gel Weakens Structure

Acid Weakens Structure

Enzymes Bromelin Papain Actinidin Ficin

Salts Strengthens Structure

Added Solid Ingredients WeakenSmall Amount Finely Chopped Just before Gel Sets


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GEL TINSWhipping Whip or Sponge

Gel Combined w/Beaten Egg Whites or Whipped Cream

Foam Increase 2-3 x Volume

Storage Dried Cool Dry Many Months

Too Long Lose Ability to Hydrate

Prepared Serve Immediately

collagen presentation

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