Chapter 6: Macromolecules
Introduction
- Macromolecules are high molecular weight compounds consisting of a large number of
monomers connected through chemical bonds
- Macromolecule = a polymer
- Primary macromolecules in food; proteins and polysaccharides
Proteins
- Monomers = amino acids
- Linkage = peptide bonds
- Added to foods for nutritional value but also as thickening or structuring agents
- Casein, β-lactoglobulin
Polysaccharides
- Monomers = glucose
- Linkage = glycosidic linkage
- Used as emulsifiers, stabilizers, gelling agents and viscosity builders
- Cellulose, starch, xantham gum, Gum Arabic
Chemical categorization of polymers
1. Homo-polymers: consisting of a single monomer species (-AAA-)
2. Co-polymers: consisting of multiple monomer species
o Random co-polymers (-ABACEDCAEDCA-)
o Alternating co-polymers (-ABABABABA-)
o Block co-polymers (-AAAABBBB-)
alginate
o Grafted co-polymers (-AAA- main chain with -BBBB- side chains)
- Monomers have a neutral charge
- When monomers bear a charge, they are called polyelectrolytes
o Monomers all positively charged = polycation
o Monomers all negatively charged = polyanion
o Monomers both positively and negatively charged = polyampholytes
Proteins are polyampholytes
pH below IEP positive
pH above IEP negative
- Monomers can also be categorized based on their shape
o Linear polymers
o Branched
o Grafted
o Ring
o Star
, Configuration of macromolecules in solution
- Macromolecule solutions have properties that differ largely from that of a monomer
solution of the same concentration
- Macromolecules solutions have a much higher viscosity
- Viscosity is an expression of the limitation of movement in the molecule
- Polymer solutions show elastic behavior, which is generally absent in monomer solutions
- This is because of the configuration the macromolecule assumes when in solution
- This configuration is a result of the connectivity of the monomers in the chain, the
interactions between various parts of the chain, interactions of chain segments with
dissolving medium & thermal energy
Tuning parameters for thickening effect
Concentration: increase concentration results in more entanglement and the viscosity increases
Length: Longer chain, average diameter is larger. Better thickening functionality.
Stiffness: Flexible molecule will fold up more easily, smaller average diameter of the coil.
Stiff molecule will have less folding ability, larger diameter of the coil.
Therefore, stiffer molecule is the better thickener
Size of coil
Ideal chains
Assume;
- Chains do not have interactions with other chains
- Chains do not have excluded volume interactions
Two extreme cases of ideal chains;
1. Very flexible chains
o Bond angle between adjacent monomers in the chain can have any value between
0 360
o Flexible polymers can assume a large number of possible configurations
o The reason for the different configurations is the thermal energy
2. Rod-like chains
Introduction
- Macromolecules are high molecular weight compounds consisting of a large number of
monomers connected through chemical bonds
- Macromolecule = a polymer
- Primary macromolecules in food; proteins and polysaccharides
Proteins
- Monomers = amino acids
- Linkage = peptide bonds
- Added to foods for nutritional value but also as thickening or structuring agents
- Casein, β-lactoglobulin
Polysaccharides
- Monomers = glucose
- Linkage = glycosidic linkage
- Used as emulsifiers, stabilizers, gelling agents and viscosity builders
- Cellulose, starch, xantham gum, Gum Arabic
Chemical categorization of polymers
1. Homo-polymers: consisting of a single monomer species (-AAA-)
2. Co-polymers: consisting of multiple monomer species
o Random co-polymers (-ABACEDCAEDCA-)
o Alternating co-polymers (-ABABABABA-)
o Block co-polymers (-AAAABBBB-)
alginate
o Grafted co-polymers (-AAA- main chain with -BBBB- side chains)
- Monomers have a neutral charge
- When monomers bear a charge, they are called polyelectrolytes
o Monomers all positively charged = polycation
o Monomers all negatively charged = polyanion
o Monomers both positively and negatively charged = polyampholytes
Proteins are polyampholytes
pH below IEP positive
pH above IEP negative
- Monomers can also be categorized based on their shape
o Linear polymers
o Branched
o Grafted
o Ring
o Star
, Configuration of macromolecules in solution
- Macromolecule solutions have properties that differ largely from that of a monomer
solution of the same concentration
- Macromolecules solutions have a much higher viscosity
- Viscosity is an expression of the limitation of movement in the molecule
- Polymer solutions show elastic behavior, which is generally absent in monomer solutions
- This is because of the configuration the macromolecule assumes when in solution
- This configuration is a result of the connectivity of the monomers in the chain, the
interactions between various parts of the chain, interactions of chain segments with
dissolving medium & thermal energy
Tuning parameters for thickening effect
Concentration: increase concentration results in more entanglement and the viscosity increases
Length: Longer chain, average diameter is larger. Better thickening functionality.
Stiffness: Flexible molecule will fold up more easily, smaller average diameter of the coil.
Stiff molecule will have less folding ability, larger diameter of the coil.
Therefore, stiffer molecule is the better thickener
Size of coil
Ideal chains
Assume;
- Chains do not have interactions with other chains
- Chains do not have excluded volume interactions
Two extreme cases of ideal chains;
1. Very flexible chains
o Bond angle between adjacent monomers in the chain can have any value between
0 360
o Flexible polymers can assume a large number of possible configurations
o The reason for the different configurations is the thermal energy
2. Rod-like chains
