polyphenolics- lec 3 Flashcards
What is the definition of Polyphenols? what are other terms for them?
Umbrella term for plant compounds with multiple phenolic groups
-polyphenols, polyphenolics, phenolic compounds
One or more -OH groups attached to an aromatic ring
What are the roles of phenolic compounds in plants?
Functions include:
* Pigments (attractants for pollinators)
* Defense against abiotic stress (UV radiation, salinity, temperature extremes)
* Defense against biotic stress (insects, bacteria, fungi, herbivores)
How can phenolic compounds be classified based on carbon skeletons?
Classification includes:
* C6–C1: Hydroxybenzoic acids (e.g., Gallic acid)
* C6–C3: Hydroxycinnamic acids (e.g., Caffeic acid)
* C6–C3–C6: Flavonoids (e.g., Quercetin)
* C6–C1–C6: Xanthones (e.g., Mangiferin)
* C6–C2–C6: Stilbenes (e.g., Resveratrol)
What is the most abundant type of polyphenol?
flavanoids
What characterizes Hydroxybenzoic Acids?
A single benzene ring with a carboxylic acid and hydroxyl groups
Examples include Gallic acid, Protocatechuic acid, salicylic acid and 4-Hydroxybenzoic acid.
What is the definition of Tannins? why are they important?
Polyphenols capable of precipitating proteins (the ‘tanning’ effect)
-found in many plant-based foods and are important for their taste (astringency), protein binding ability and antioxidant properties
What are the types of Hydrolyzable Tannins? where are they found?
Types include:
* Gallotannins: gallic acid units esterified to glucose
* Ellagitannins: ellagic acid units formed from oxidative coupling of gallic acid
- found in strawberry, raspberry, mago aged wines and spirits
What is the structure of C6–C3 compounds? provide an example
Plant phenolics consisting of a benzene ring (C6) and a propene side chain (C3)
Key examples include Caffeic acid, and Ferulic acid.
What is the significance of the carboxylic acid group (–COOH) in C6–C3 compounds?
It contributes to solubility and reactivity
-it can be a site for esterification
What are chlorogenic acids (CGAs)?
Esters of caffeic acid with quinic acid, serving as a major class of water-soluble antioxidants
What are flavonoids? what structure do they exhibit? what does this mean?
A large class of polyphenolic compounds with a structure of C6–C3–C6
-2 aromatic rings (C6) linked by a 3C bridge
What are anthocyanidins?
Water soluble, glycosylated form of flavanoid
-anthocyanins responsible for red, blue, and purple colors in fruits and flowers.
What are proanthocyanidins? what are they also reffered to as? what is their importance?
Also called condensed tannins, these are a subclass of flavonoids (larger flavanoid units)
-contribute to astringency and color stability in wine
What is the functional significance of procyanidins? where are they found?
They contribute to astringency, bitterness, antioxidant activity, and color stabilization
-found in grape skin, seeds and stem tissues of fruit
what factor in procyanidins plays a large role in the properties they exhibit?
the change in linkage between A1-A2 procyanidin
How does the degree of polymerization impact sensory perception? what is the effect of ripening?
smaller units (4-5) exhibit bitter taste
larger units (7-8) exhibit atringent tastes
-ripening will decrease bitterness/astringency
What is glycosylation? what is its impact? how does the main site of glycosylation differ for flavanols vs flavones?
glycosylation is the attachment of sugar to the flavanoid backbone
-increases solubility, alters taste, increases stability during processing, changes bioavailibity
flavones main site is in position 7
flavanols main site is in position 3
What are the similarities / differences of flavanols vs flavones?
Both subclasses of flavonoids:
Flavanols: powerful antioxidants, astringent + bitter
-most common flavonoids in foods (outer skin/tissues)
Flavones: anti-inflammatory, less bitter
What are isoflavones?
class of flavonoid found primarily in legumes
-mimic/block estrogen depending on tissue type/ hormone environment (similar structure to estrogen)
-may help treate postmenopausal symptoms
What are anthocyanins and what is the basic structure of them? what colour do they exhibit?
Glycosylated forms of anthocyanidins with a flavylium cation
-water soluble pigments giving blue, purple, red and orange colours
-different colours are present depending on the R group
where are sugars bound in anthocyanins? what occurs when it loses its sugar?
bound at positions 3 and 5
-the loss of the sugar results in the formation of less soluble anthocyanidin
how does the addition of OH vs OCH3 groups change the colour of anthocyanidins?
more OH groups = more blue
more OCH3 groups = more red
What happens to anthocyanins at pH <3, 4-5, 6-7 and 7-8?
pH <3 = red
pH 4-5 = colourless
pH 6-7 = purple
pH 7-8 = yellow or blue
What are glycosidases and polyphenol oxidases? what do these have in common?
1) polyphenol oxidase
-aids in the production of oxidised anthocyanins (important for colour production)
2) glycosidases (main one)
-cleave sugars to reduce solubility (loss of colour intensity -> colourless products)
-found in the peel
these are anthocyanases (enzymes that catalyze breakdown of anthocyanins)
