Phenolic compounds
Introduction
Present in many foods, predominantly in plant foods (berries, tea, red wine) and hardly in animal
products
Properties of phenolic compounds that are important in food;
1. Colour
2. Can cause browning reactions
3. Complexation with proteins
- Precipitation/haze formation
- Astringency
4. Induction of taste
5. Anti-oxidative properties in foods
6. Associated with health effects (antioxidants)
Basic skeleton
Compounds with a benzene ring + hydroxyl group (-OH)
The basic skeleton can be substituted by;
- Multiple -OH groups
- Aliphatic C-chains
- Another benzene ring
Other names: polyphenols or phenolics
Phenolic compounds are abundant in;
- Coffee
- Tea
- Cocoa
Classification based on C-skeleton
, - Classification can also be done based on the occurrence of phenolic compounds
in the free or bound form
Question from slides
Answer to Q1: only plant products; apple,
almonds, wheat
Mono-/dimeric phenolic compounds
Monomeric example: Hydroxycinnamic acid (derivatives)
Occurrence of Hydroxycinnamic acid (derivatives);
- as free molecules
- as an ester bound to mono- or oligosaccharides
- as an ester of polysaccharides (wheat arabinoxylans)
Properties in foods;
1. binding to metal ions
- example: Fe-chlorogenate complex in potatoes
- just after harvesting the potato the iron present in the potato becomes bound to
citric acid. This complex is colourless.
- Therefore, if we cook potatoes just after harvesting we do not notice a
discolouration
- Upon storage of the potatoes there is no citric acid left and the iron complexes
with chlorogenate to form a black complex
- Darkening noticed in the potato after cooking
, 2. Substrate for enzymatic oxidation (especially chlorogenic acid)
- Enzymatic oxidation is caused by polyphenol oxidase
- Polyphenol oxidase oxidizes the -OH groups present in the phenolic compound
to a quinone moiety
- Once it is oxidized the phenolic compound polymerizes into brown pigments
Dimeric example: Flavonoids and isoflavonoids
- Contain 2 benzene rings
Structure
Basic C6C3C6 structure
Oxidized middle C-ring (pyran)
Flavonoids: subclasses
Classification is based on the oxidation level of the C-ring
Occurrence
- Free of bound to sugars
- In many plants (for protection against UV light, attraction of insects)
Properties in foods
- Biological properties (estrogenicity)
- Antioxidant
- Give colour to foods (anthocyanins)
- Substrate for enzymatic oxidation
Introduction
Present in many foods, predominantly in plant foods (berries, tea, red wine) and hardly in animal
products
Properties of phenolic compounds that are important in food;
1. Colour
2. Can cause browning reactions
3. Complexation with proteins
- Precipitation/haze formation
- Astringency
4. Induction of taste
5. Anti-oxidative properties in foods
6. Associated with health effects (antioxidants)
Basic skeleton
Compounds with a benzene ring + hydroxyl group (-OH)
The basic skeleton can be substituted by;
- Multiple -OH groups
- Aliphatic C-chains
- Another benzene ring
Other names: polyphenols or phenolics
Phenolic compounds are abundant in;
- Coffee
- Tea
- Cocoa
Classification based on C-skeleton
, - Classification can also be done based on the occurrence of phenolic compounds
in the free or bound form
Question from slides
Answer to Q1: only plant products; apple,
almonds, wheat
Mono-/dimeric phenolic compounds
Monomeric example: Hydroxycinnamic acid (derivatives)
Occurrence of Hydroxycinnamic acid (derivatives);
- as free molecules
- as an ester bound to mono- or oligosaccharides
- as an ester of polysaccharides (wheat arabinoxylans)
Properties in foods;
1. binding to metal ions
- example: Fe-chlorogenate complex in potatoes
- just after harvesting the potato the iron present in the potato becomes bound to
citric acid. This complex is colourless.
- Therefore, if we cook potatoes just after harvesting we do not notice a
discolouration
- Upon storage of the potatoes there is no citric acid left and the iron complexes
with chlorogenate to form a black complex
- Darkening noticed in the potato after cooking
, 2. Substrate for enzymatic oxidation (especially chlorogenic acid)
- Enzymatic oxidation is caused by polyphenol oxidase
- Polyphenol oxidase oxidizes the -OH groups present in the phenolic compound
to a quinone moiety
- Once it is oxidized the phenolic compound polymerizes into brown pigments
Dimeric example: Flavonoids and isoflavonoids
- Contain 2 benzene rings
Structure
Basic C6C3C6 structure
Oxidized middle C-ring (pyran)
Flavonoids: subclasses
Classification is based on the oxidation level of the C-ring
Occurrence
- Free of bound to sugars
- In many plants (for protection against UV light, attraction of insects)
Properties in foods
- Biological properties (estrogenicity)
- Antioxidant
- Give colour to foods (anthocyanins)
- Substrate for enzymatic oxidation
