Plant Tannins

Question 1

What are Tannins?

Answer 1

• Functional defn: Large polymeric polyphenols with protein-binding (and precipitating ability)
• Have aromatic rings (hydrophobic interactions) and Hydroxyls (can form H-bonds)

Question 2

How are tannins found in plants?

Answer 2

• As variable and heterogeneous mixtures (dimers, oligomers, polymers)

Question 3

What are the 2 major types of tannins in plants?

Answer 3

• Hydrolyzable tannins

- Condensed tannins

Question 4

Where are tannins found in high concentrations?

Answer 4

• Tree bark roots, and leaves

- Forest system litter and soils

Question 5

What is the most abundant ‘natural product’ on the planet?

Answer 5

• Tannins, as secondary metabolite

Question 6

What kind of biological effects do tannins have?

Answer 6

• Diverse biological effects

- Anti-feedant, antimicrobial, antioxidant

Question 7

Where are people interested in tannins?

Answer 7

• Tanning leather
• Flavour and stability of beer and wine
• Found in many natural foods
• Important for healthy diet
• Strong in-vitro antioxidants
• Impact gut micro biome
• Cattle feed
• Prevent bacterial adhesion

Question 8

Why are tannins good for leather?

Answer 8

• Bind protein, prevent bacterial growth, soften leather

Question 9

Tannins and beer and wine

Answer 9

• Flavour and stability
• Give dry mouth-feel, puckering
• In wine, come from grape skin and oak wood
• In beer, come from barley and hops
• Beer haze is a tannin-protein precipitate

Question 10

What ‘natural foods’ are tannins found in?

Answer 10

• Nuts, grains, lentils, and beans (in seed coat), berries and other fruit (skin and seeds)

Question 11

What foods are found to have highest concentration of tannins?

Answer 11

• Cocoa, cinnamon, persimmon, apple, blueberry, salal

Question 12

Why are tannins important for a healthy diet?

Answer 12

• linked to reduced risk of cardiovascular disease, metabolic syndrome, neurodegenerative disorders, and more

Question 13

Antioxidants and tannins

Answer 13

• Strong in-vitro but in-vivo not clear

Question 14

Which tannins are found to inhibit bacterial adhesion?

Answer 14

• Cranberry A-type condensed tannins

Question 15

Tannins in cattle feed

Answer 15

• Improve nitrogen uptake
• Prevent cattle bloat
• Reduce methane release (inhibit rumen protein breakdown)

Question 16

Why do plants make so much tannin?

Answer 16

• Anti-nutritive defences against herbivores (binds proteins at neutral or acidic pH)
• Defend against pathogens
• Protect seeds from stress by sealing the seed coat
• May act as in vivo antioxidants to protect against stressful oxygen radicals
• Influence N cycling in soils
• Protect against metal toxicity

Question 17

Tannins and metal toxicity

Answer 17

• Protect soil from metal toxicity of Al and bind iron (Fe)

Question 18

Tannins as an anti-feedant example

Answer 18

• Ex. Beavers prefer low-tannin aspen bark, tree feeding caterpillars not so much

Question 19

Example of Tannins as defines against pathogens

Answer 19

• Act as antimicrobials

- High tannin poplars are more resistant to poplar rust

Question 20

How do tannins influence N cycling in soils?

Answer 20

• Inhibiting bacteria but not mycorrhizal fungi

- Litter bag experiments show that tannins slow decomposition