Carbohydrates / Polysaccharides - Storage polysaccharides - Chemical modification

23 important questions on Carbohydrates / Polysaccharides - Storage polysaccharides - Chemical modification

Why do you modify starch under 50 degrees?

Because otherwise it gelatinizes. And you don't wand that yet. And you can not deal with a gel.

What are the things that make chemical modification difficult?

  • Different ‘reactivity’ depending on granule size
  • Crystalline versus amorphous regions
  • Amylose versus amylopectin (amylose is more easy to modify)
  • Distribution within the amylose/amylopectin molecule

How do you crosslink your starch?

You add sodium-trimetaphosphate
At pH11.5 it will make a phosphore ester and this makes that the starches can be linked at certain places.
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What is the effect of crosslinking starch?

The effect is a hihger gelatination temprature and a higer viscosity when cooling down.

  • They also keep swollen granules intackt
  • Prevent loss of viscosity
  • Resistant to mechanical shear
  • more stable in acid conditions 

What is the reason behind the effects of crosslinked starch?

If starch is connected it is harder for the granulas to swell. This leads to a increase of gelatination temprature.
This results in a stabler product since it is hard to break the granulas.

Why do you often do more modifications then only crosslinking?

This is done because crosslinking does not work against retrogradation. Because you can not be sure there are also crosslinks between the amylose. So they can not pile up and reform a cristaline network.

What are stabilisation reactions?

Reactions that modify the pectin in a way that no retrogradation can happen.

What is the degree of subsitution?

This is the level of substituents of the hydroxyl groups along the starch chains.

What are the places which can have a substituent in a glucose molecule in a starch chain?

O-2, O-3 and O-6

How do they call starch that had a esterification step?

Acetylated starch

What are the reactions occuring during esterification of starch?

one primary riaction and 2 side chain reactions.

What is the effect on viscosity of acetylated corn starch?

The granulas are pushed a bit more loose. So you will have a higher viscosity. They will also fall appart more easaly so the streght is less.

What is succinate starch?

It is produced by the reaction of starch with succinic anhydrite at pH 8.

What are the properties of succinate starch?

Due to the O- (free carboxylate group) you can have a bigger water holding capacity and the tendency to swell in cold water.
It also increases the viscosity

By what can you controll the properties of succinate starch?

PH and salt.

Low pH less coo- loading so less viscous solution

High pH more coo- loading so more viscous solution.

High salt neutralises coo- loading so less viscous

How do you get starch monophosphate?

By adding phosphate

Same properties as succinate starch due to charge.

What is the difference in stability between a ester and ether linkage in starch?

Ether linkages are stable with high pH. Ester linkages not.

What are the improvements that etherification gives to starch?

Improved clarity, viscosity stability and cold storage stability.

It limits the tendency of cold retrogradation.  

less degradable by enzymes

What is the special property of hydropropyl starch?

A strong gel at high tempratures.

How can you give hydropropyl starch a hydrophobic caracter?

By addid more groups to the side chian.

How can you control the viscosity of hydroxypropyl starch?

By oxidaton.

What is cationization of starch?

Starch is given a positive ionic charge by introducing ammonium, amino, sulfonium or phosphonium group.

What are the properties of cationization of starch?

lower gelatinization temprature
higher peak viscosity
applications in paper indsutry.

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