Cellulose and Starch modification

Question 1

Why to modify hydrocolloids?

Answer 1

• Improve functional properties
  
  • Viscosity
  • Gelling
  • Interaction with other food polymers
  • Emulsifying properties
• > 70% of all starches and major part of cellulose in food application has been modified to some extend.

Question 2

CELLULOSE: source and structure

Answer 2

Originate from plant cell wall material.

*The beta-1,4-chains are organized in fibrils cellulose, fibrils which can be isolated quite easily.

Question 3

Benefits of polysaccharide modification

Answer 3

• You can make cellulose soluble and more functional.
• Native starches show defects in their functionality in particular applications, make better properties.
• Various ways of modification of starch to change one or more of following properties of e.g. starch:
• Pasting temperature
• Solids-viscosity relationships
• Gelatinisation and cooking characteristics
• Resistance of starch pastes to breakdown in viscosity by acids, heat and/or mechanical shear
• Retrogradation tendencies
• Ionic character
• Hydrophilic character

Question 4

Derivatisation of starches and cellulose. How is done?

Answer 4

• Swelling under mild alkaline conditions (always in solid state).
• Modification very often not homogenous
• Starch modification mainly on starch granules. T«50˚C
• Multiple levels of complexity
• Small vs. large granules
• Crystalline vs. amorphous regions (crystalline regions more difficult to penetrate).
• Amylose vs. amylopectin
• Amylopectin backbone vs. side chains

Question 5

Name the three cellulose derivatives:

Answer 5

1.Carboxymethylcellulose: CH2- C=O , O-
2.Hydroxypropylcellulose:CH2-CH-CH3,OH
3.Methylcellulose: -CH3 (typical high temperature gelling behaviour).
All these three substituents are linked C-O-C which is quite a stable substituent, a stable derivative. Ether linkage (charge is present in the substituent COO-)

Question 6

Describing the modification: Degree of substitution (DS)

Answer 6

Is the number of substituents per glucose residue, since we have three hydroxyl groups available the maximum level of DS of starch is 3-.
*1 glucose unit can be substituted at 3 locations (O-2, O-3 and O-6)

Question 7

Describing the modification: Molar Substitution (MS)

Answer 7

This is different when the substituent has its own hydroxyl group. In the case of hydroxypropyl group you have an hydroxyl group present which could be target by a next substitution making the side chain longer and longer and more hydrophobic in this case.
Molar substitution: number of moles substituents per mol of glucose, that could be much higher than three.

Question 8

Why are starch and cellulose the most commonly used

polymers to be modified?

Answer 8

Both polymers are insoluble and it is really easy to remove excess of reagent and to obtain the pure modified polymer, dry nice powder.
A soluble polysaccharides is much more difficult to recover in down stream processing.