I have made a summary of chapter 6 of the reader Food Technology. Together with the other summaries of the chapter, it'll be a great preparation for the exam. I hope it is useful for you!
Macromolecules are also called polymers and they have a huge impact on the sensory
and textural properties of food. They are often used as thickeners.
Large molecules consist of sub-units. Poly-ethylene consists of many ethylene units.
The shape of polymers can differ a lot. Some might be branched, others linear, for
instance.
Macromolecules that are used as thickeners in food, belong mainly to proteins and
polysaccharides.
o Protein: polymer of amino acids (ovalbumin).
o Polysaccharide: polymer of sugars (cellulose).
Units are monomers. They are symbolized by A, B, C,…
o Homo-polymers: A-A-A.
Cellulose with solely glucose units.
o Co-polymers.
Alternating: -A-B-A-B.
Random: -A-B-E-A-B-E-C.
Block-co-polymers: -A-A-A-B-B-B-A-A-A.
Grafted: A-A-A main chain with B-B side chains.
Macromolecules can also be categorized based on charge:
o Poly-cations: -A+-A+-A+-.
o Poly-anions: -A—A—A--.
o Poly-ampholytes: -A+-B- (proteins).
Poly-cations + poly-anions + poly-ampholytes = poly-electrolytes.
The overall charge of a poly-ampholyte is pH dependent. The pH determines the charge
of the COOH- and NH2-groups in the molecule.
o Each protein has a specific amino acid sequence and therefore also a specific
COOH- and NH2-group composition.
o The pH at which the charge of the COOH-groups balances that of the NH2-
groups, is called the isoelectric point (pI).
pH << pI: positive charge.
pH >> pI: negative charge.
Consider 2 solutions:
o Solution (1): glucose in water solution.
o The glucose molecules are free to
move/flow in the water.
o Solution (2): cellulose in water solution.
o There are limitations in movement, due to
intramolecular bonds.
, Upon doubling the glucose monomers in solution (1) and
upon adding another cellulose molecule to solution (2),
the following occurs:
o Solution (1): the glucose monomers can still
move freely.
o Solution (2): the cellulose molecules are now
not only limited by intramolecular bonds, but
also by the possibility that the two chains can
entangle.
When you let the two solutions flow to a funnel, solution
(1) will flow quickly through the funnel, because. Of the free
movement of the glucose monomers. Solution (2) will move
more slowly, due to internal and mutual connectivity of
the cellulose chains.
o A slow flow corresponds with an increased
viscosity. This means that solution (2) would be
thicker.
So, a macromolecular solution has a much higher viscosity than a monomeric solution.
They also show elastic behavior.
Concept of a random coil:
- Random coil: a polymer conformation in which the monomer subunits in the chain are
oriented randomly.
o There is no defined structure; therefore it is most easy to picture the coil as a sphere
in which the polymer is enclosed.
o The configuration of a random coil is the result of the connectivity of the monomers
in the chain, the interactions between various parts of the chain, the interactions of
chains segments with the dissolving medium, and thermal energy.
Each factor that increases the possibility of entanglement, or the possibility of
connectivity between polymer molecules, also increases thickening:
1. Increase in concentration.
2. Increase of the macromolecule chain length.
3. Stiff molecules, instead of flexible molecules.
4. Increase in coil size.
o A coil is large when the chain is long and stiff.
- Ideal chains: chains that do not have any interaction with the solvent. They also don’t have
excluded volume interactions (they don’t feel other parts of the chain/ there can be
crossings without energy penalties). There can be 2 extreme cases:
o Very flexible chains:
The bond angle between adjacent monomers in the chain can take any value
between 0 and 360o. they can assume an enormous number of distinct
configurations, very rapidly. This is because of the thermal energy of the
solvent molecules, due to the fact that there is an absolute temperature
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