Phenolic compounds Flashcards
What does a stillbenoids skeleton look like?
C6C2C6
What does a flavonoid skeleton look like?
C6C3C6
What is the difference between lignins and lignans?
Lignans are dimers or trimers whereas lignins are polymers.
Both are made of hydroxycinnamic acids and/or hydroxycinnamyl alcohols.
Which type of phenol can cause indigestibility?
Flavanols when interaction with proteins takes place (condensed tannins).
Why are tannins important in food?
They can interact with proteins and greatly influence food properties.
What are the two types of PPO activity and how can they be distinguished from eachother?
1) Catecholase activity:
- Converts o-diphenols to o-quinones (using oxygen and producing water).
- o-quinone has two subsequent doublebonded oxygens at the ring.
2) Cresolase activity:
- Converts monophenols to o-diphenols (using oxygen)
- o-diphenol has two subsequent OH-groups at the ring
Catecholase is the preferred reaction of PPO. It may also use the product of the cresolase reaction (o-diphenol) for the catecholase reaction. Catecholase activity is faster than cresolase.
Give a phenolic compound which determines colour dependent on pH.
Anthocyanins. (Red-purple-blue)
- Flavylium cation is positively charged at low pH and gives a red colour
- Quinoidal base is neutrally charged at slightly higher pH and is purple
- Quinoidal anion is positively charged at neutral pH and has a blue colour.
When the first two interact with water, they convert to a colourless carbinol pseudo base (conjucated system is lost). This can occur in equilibrium with its ring-opened form chalcone which is yellow.
What makes o-quinones prone to nucleophilic attack?
Their electron deficient nature.
When does a phenolic compound have colour?
When the phenol has at least seven conjugated double bonds.
What configurations of hydroxycinnamic acids occurs the most in nature?
Trans.
What are the main phenolic compounds in tea leaves and green tea?
Flavan-3-ols (catechins).
At what degree of polymerization are the condensed tannins perceived as most astringent, and why?
Astringency of condensed tannins is typically highest in the range of degree of polymerization 5 to 7, when binding is relatively strong and the oligomers are still somewhat soluble.
