Summary
Phenolic compounds summary food chemistry (FCH20806)
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Complete summary of the information needed to understand phenolic compounds during this course.
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Phenolic compoundsIntroduction
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
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