Summary Food Ingredient Functionality – FCH30306 WUR
Polysaccharides
Physicochemical properties of polysaccharides
Polysaccharide building blocks
• Homoglycans: polysaccharides that consists out of the same monosaccharide
• Heteroglycan: polysaccharides that consist out of different monosaccharides
• The type of linkage between the monosaccharides (for instance alpha or beta) determines the
flexibility and stability of the polysaccharide.
Molecular weight
• High molecular weight → high viscosity
• Poly dispersed: there is a difference is the size of the polysaccharide molecules
• Mono dispersed: all polysaccharide molecules have the same size
• Hydrodynamic volume: the volume occupied by the molecule in solution
o Linear molecule → high hydrodynamic volume
o Dense, branched polysaccharide → lower hydrodynamic volume (because if 10 units
are branched, the radius is smaller than were they are linear next to each other)
Solubility and molecular interactions
• Branched molecules are more soluble than linear molecules because they have a lower
hydrodynamic volume
• Branched molecules have side chains so they cannot form junction zones with their selves. This
would decrease solubility.
• Repulsion in a molecule makes in hard for the molecule to form junction zones with itself →
better solubility
Charge
• Polysaccharides can contain uronic acid.
o Galacturonic acid in pectin
o Glucuronic acid in xanthan gum
o Mannuronic acid and guluronic acid in alginate
• These have a carboxylic acid group that can have a negative charge!
o pH = pKa → 50% neutral, 50% negative
o pH < pKa → neutral
o pH > pKa → negative
• Charge can also come from sulphate, phosphate or pyruvate (CH3-C-COOH)
Esterification and amidation
• Carboxyl group of uronic acids can be esterified
o Pectin can be esterified with methyl
o More esterified → less charge is possible
o Distribution of methyl esters over the pectin backbone determines the charge density
of the pectin molecule and its ability to interact with bi-valent ions like calcium.
• Carboxyl groups can be amidated
o A part of the carboxylic group is converted to an amide group
o Amidated pectin has different calcium binding and gelling properties.
, Analytical techniques
Molecular weight distribution
What?
Study the molecular weight distribution (hydrodynamic volume / size) of polysaccharides and
monitor the effect of modification.
How?
High Performance Size Exclusion Chromatography (HPSEC) where larger molecules are less
retained by the column compared to smaller molecules. Early peak = large molecule!
Monosaccharide composition
What?
Determine the carbohydrate composition.
How?
Hydrolysing polymer into its monomers (glucose, galactose etc.) and analysis of these monomers
by
• High Performance Liquid Chromatography (HPLC) or Gas Chromatography (GC) → for neutral
sugars
• High Performance Ion Exchange Chromatography → for both neutral and uronic acids
Degree of methylation, acetylation and amidation
What?
Determining the ester level of polysaccharide
How?
Saponification under alkaline conditions. Ester groups are released.
• Methanol can be quantified by GC or spectrophotometric colour essay (mole methanol/100
moles galacturonic acid)
• Acetic acid can be quantified by enzymatic colour assay, HPLC or GC (mole acetic acid/100
moles of sugar residues)
Level of amidation: presence and level of nitrogen is taken as measure for level of amide groups.
Anionic hydrocolloids
What?
Anionic = can become negatively charged
So the presence of negatively charged polysaccharides
How?
• Complex formation with methylene blue to determine if negative/ neutral
• Distinction between different anionic polysaccharides → sugar composition analysis
• Quick gel formation upon addition of calcium → pectin or alginate
• Presence of pectins → presence of esterified methanol by GC
• Rhodizonate colour assay → carrageenan (sulphate group binds with rhodizonate)
Degradation of polysaccharides using specific enzymes
What?
Distinguish between different types of polysaccharides
How?
Using enzymes that have a high specificity for specific carbohydrate building blocks or specific
linkage types. After that measuring molecular weight by HPSEC or HPAEC-PAD.
Polysaccharides
Physicochemical properties of polysaccharides
Polysaccharide building blocks
• Homoglycans: polysaccharides that consists out of the same monosaccharide
• Heteroglycan: polysaccharides that consist out of different monosaccharides
• The type of linkage between the monosaccharides (for instance alpha or beta) determines the
flexibility and stability of the polysaccharide.
Molecular weight
• High molecular weight → high viscosity
• Poly dispersed: there is a difference is the size of the polysaccharide molecules
• Mono dispersed: all polysaccharide molecules have the same size
• Hydrodynamic volume: the volume occupied by the molecule in solution
o Linear molecule → high hydrodynamic volume
o Dense, branched polysaccharide → lower hydrodynamic volume (because if 10 units
are branched, the radius is smaller than were they are linear next to each other)
Solubility and molecular interactions
• Branched molecules are more soluble than linear molecules because they have a lower
hydrodynamic volume
• Branched molecules have side chains so they cannot form junction zones with their selves. This
would decrease solubility.
• Repulsion in a molecule makes in hard for the molecule to form junction zones with itself →
better solubility
Charge
• Polysaccharides can contain uronic acid.
o Galacturonic acid in pectin
o Glucuronic acid in xanthan gum
o Mannuronic acid and guluronic acid in alginate
• These have a carboxylic acid group that can have a negative charge!
o pH = pKa → 50% neutral, 50% negative
o pH < pKa → neutral
o pH > pKa → negative
• Charge can also come from sulphate, phosphate or pyruvate (CH3-C-COOH)
Esterification and amidation
• Carboxyl group of uronic acids can be esterified
o Pectin can be esterified with methyl
o More esterified → less charge is possible
o Distribution of methyl esters over the pectin backbone determines the charge density
of the pectin molecule and its ability to interact with bi-valent ions like calcium.
• Carboxyl groups can be amidated
o A part of the carboxylic group is converted to an amide group
o Amidated pectin has different calcium binding and gelling properties.
, Analytical techniques
Molecular weight distribution
What?
Study the molecular weight distribution (hydrodynamic volume / size) of polysaccharides and
monitor the effect of modification.
How?
High Performance Size Exclusion Chromatography (HPSEC) where larger molecules are less
retained by the column compared to smaller molecules. Early peak = large molecule!
Monosaccharide composition
What?
Determine the carbohydrate composition.
How?
Hydrolysing polymer into its monomers (glucose, galactose etc.) and analysis of these monomers
by
• High Performance Liquid Chromatography (HPLC) or Gas Chromatography (GC) → for neutral
sugars
• High Performance Ion Exchange Chromatography → for both neutral and uronic acids
Degree of methylation, acetylation and amidation
What?
Determining the ester level of polysaccharide
How?
Saponification under alkaline conditions. Ester groups are released.
• Methanol can be quantified by GC or spectrophotometric colour essay (mole methanol/100
moles galacturonic acid)
• Acetic acid can be quantified by enzymatic colour assay, HPLC or GC (mole acetic acid/100
moles of sugar residues)
Level of amidation: presence and level of nitrogen is taken as measure for level of amide groups.
Anionic hydrocolloids
What?
Anionic = can become negatively charged
So the presence of negatively charged polysaccharides
How?
• Complex formation with methylene blue to determine if negative/ neutral
• Distinction between different anionic polysaccharides → sugar composition analysis
• Quick gel formation upon addition of calcium → pectin or alginate
• Presence of pectins → presence of esterified methanol by GC
• Rhodizonate colour assay → carrageenan (sulphate group binds with rhodizonate)
Degradation of polysaccharides using specific enzymes
What?
Distinguish between different types of polysaccharides
How?
Using enzymes that have a high specificity for specific carbohydrate building blocks or specific
linkage types. After that measuring molecular weight by HPSEC or HPAEC-PAD.
