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ZZ2 > Flavonoids > Flashcards

Flavonoids Flashcards

1
Q

What are polyphenols?

A
  • Abundant group (>8000) of plant metabolites
  • Range from simple phenolic molecules to highly polymerized compounds (anti-nutrients; eg. tannin)
  • Contributes to plant physiology (growth, reproduction) and morphology (pigmentation)
  • Provides plants with resistance to pathogens and threats
  • Interest due to antioxidant capacities, etc.
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2
Q

What is the common structural feature of all polyphenols?

A

Aromatic ring with at least 1 hydroxyl group

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3
Q

What are the 2 pathways that polyphenols are synthesized from?

A
  1. Shikimate

2. Acetate

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4
Q

Discuss polyphenol content in plants and the variables that may affect it.

A
  • There is variation even within a plant species
  • Hard to figure out exact content

VARIABLES:

  • Light (highest concentration in leaves except onion + garlic)
  • Genetic factors
  • Environmental conditions (temperature, humidity)
  • Germination
  • Degree of ripeness
  • Variety
  • Processing
  • Storage
  • Lab sensitivity
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5
Q

What properties do phytochemicals increase in food which limits innovation of food products?

A

Can increase astringency (acidity) and bitterness

Oxidation during processing or storage can cause organoleptic qualities

  • Desirable ⟶ browning of cocoa, polymerization of black tea that contributes to taste
  • Undesirable ⟶ enzymatic browning (unpleasant colour change)
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6
Q

What 2 factors do polyphenol content in food affect in our body?

A
  1. Digestibility of macronutrients
    - Highly polymerized polyphenols bind protein
    - Reduced absorption + increased fecal nitrogen
    - May affect absorption of carbs/fats by interfering with enzymes
  2. Mineral bioavailability
    - Form complexes with metal cations
    - Reduced absorption (can be a good thing if iron)
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7
Q

Who discovered flavonoids and what did they find?

A
  • Discovered by Rusznyak and Szentgorgyi ⟶ “vitamin P” (pigment)
  • Found that flavonoids enhanced function of vitamin C by protecting it from oxidation
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8
Q

What are flavonoids and where can they be found?

A
  • Subgroup of low molecular weight polyphenols (not highly polymerized)
  • Most common group + most researched
  • Present in all plants in the outer parts of the plant (skin, leaves, flowers)
  • Widely distributed in foods (vegetables, tea, cocoa, wine)
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9
Q

What is the structure of flavonoids?

A

2 aromatic rings linked through 3 carbons

Ring A (acetate pathway) with OH group attached

Ring B (shikimate pathway) with OH group

Ring C in the centre 
- Variations in C ring determines class of flavonoid
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10
Q

What are the 6 major subclasses of flavonoids?

A

(1) flavones
(2) flavonols
(3) flavonones
(4) flavanols
(5) anthocyanidins
(6) isoflavones

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11
Q

Why do we want to know flavonoid content in plants/foods? What makes that difficult?

A

We want to know how much are in foods to determine effect on body!

  1. Inappropriate application of analytic methods, making it hard to determine food content and dietary intake (contradictory info)
  2. Inconsistent use of nomenclature in description of flavonoids (studies don’t quantify which flavonoids they are measuring)
  3. Limited data of flavonoid test materials used in dietary intervention trials
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12
Q

Which databases can be used for dietary assessment of flavonoids?

A

Canadian Nutrient File + USDA database + US Department of Agriculture do not include flavonoids and cannot be used for dietary assessment

USDA Database for the Flavonoid Content of Selected Foods is a specific database for flavonoid content

  • Can create nutrition facts/labels and be used by nutritional epidemiologists to assess health
  • Only ⅚ subclasses (isoflavones has own database)

European Prospective Investigation into Cancer and Nutrition (EPIC) study used USDA database to create own FLAV database (more foods)

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13
Q

What are flavonoid glycosides?

A

Flavonoids are typically attached/conjugated to carbohydrate moieties (most often glucose) in food

If attached to sugar/carb molecule ⟶ “flavonoid glycoside” (more mg for biologically active dose)

If not attached to carbs ⟶ flavonoid aglycone (less mg; more biologically relevant, the focus for research/dietary assessment)

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14
Q

The major of flavonoids appear in plants as ___. What are the 2 functions of this?

A

Glycosides

  • Increases polarity
  • Necessary for storage of flavonoids in plant vacuoles
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15
Q

Are flavonoids bioavailable?

A
  • Yes; flavonoids are absorbed and reach concentrations of varying magnitudes in our biological fluids
  • Initially thought to be negligible since they are bound to glycosides
  • Not the case; gut bacteria produces enzyme to break down
  • Other factors ⟶ food matrix, food processing
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16
Q

What is the best biological assessment of intake of flavonoids?

A

Biomarkers in the blood/urine

  • Not biased/subjective
  • Can see bioavailability of nutrient
  • More accurate assessment of intake than databases/food questionnaires
17
Q

What do we need to measure polyphenol bioavailability?

A
  • Perfect characterization of ingested polyphenols (intake)
  • Be able to analyze metabolites in blood
  • Be able to measure biologic effect with relevant biomarkers
  • Be able to measure urinary and fecal excretion
18
Q

What biologic effects do flavonoids have in the body?

A
  1. Antioxidant
    - Direct free radical scavenger due to cyclical structure (ring) and OH group
    - Protect or regenerates vitamin E from oxidation
    - Chelete metals involved in initiation of lipid peroxidation (iron)
    - Induce antioxidant-related enzymes such as glutathione transferase (GST) which increases resistance of cells to hydrogen peroxide (H2O2) + detoxifies xenobiotics with mutagenic potential
  2. [Anti-]Hormonal
    - Estrogenic or anti-estrogenic
    - If you have a lot of estrogen and introduce weak estrogen, weak estrogen will take up receptors and decrease hormonal effect
    - Related to breast, uterine, and endometrium cancer
    - Mainly related to isoflavones (type of phytoestrogen)
  3. Anti-proliferative
    - Inhibition of cellular transformation and proliferation
    - Inhibit growth of cancer cells
    - Interact with enzymes associated with DNA
    - Eg. DNA topoisomerase II (facilitates apoptosis and creates unstable DNA)
  4. Other
    - Anti-bacterial, viral, fungal, inflammatory, allergic, mutagenic
    - Based on role in plant itself; potential relevance to disease
19
Q

What is a biomarker? What is a good one?

A
  • Substance in an organism whose presence is an indicator of disease risk or intake

GOOD:

  • Consistent biological format (doesn’t get degraded over time)
  • Specificity (does it measure what it is supposed to)
  • Sensitivity (can it be picked up)
  • Non-invasive, cost-effective, feasible
  • Have reference ranges (that we can refer to so we know if it is low/high)
20
Q

What is Relative Risk?

A

Relates risk of disease with low or high food intake (risk of treatment/risk of control)

95% CI of RR:
= 1 (hypothesis rejected, nothing going on)
> 1 (bad)
< 1 (good, protective!)

If RR = 0.50; then 50% decrease in risk!

21
Q

What do studies have to say about the health effects of flavonoids?

A
  1. Cancer
    - Contradictory; some studies found no significant associations for cancers
  2. CVD
    - Lower risk of heart attack, and stroke
  3. Diseases related to oxidative stress (aging, diabetes)
22
Q

What should product formulators consider for quality assurance of a product?

A
  1. Botanical source
  2. Type of polyphenol
    - Polyphenols can be inactive until converted into a metabolite
  3. Dose: effective and safe
  4. Form and stability of product
  5. Pesticide concentration so include testing
23
Q

What are anthocyanins?

A
  • Class of flavonoids
  • Water-soluble plant pigment
  • Responsible for pigmentation of flowers and fruits
24
Q

What is the name for glycoside/aglycone anthocyanins?

A

Glycoside ⟶ anthocyanin

Aglycone ⟶ anthocyanidin

25
Q

What is the purpose of anthocyanins for plants and animals?

A

Plant ⟶ attract animals for seed/pollen dispersal (reproduction)

Humans ⟶ enhance enjoyment of eating, may protect us against disease

26
Q

Discuss anthocyanin metabolites and bioavailability.

A
  • Low bioavailability (not recovered in urine)
  • May be due to gut metabolites that are unidentified
  • Holds up research ⟶ we want to clarify metabolites before studying effects
27
Q

What are the health effects of anthocyanins? Which one(s) are demonstrated in human studies?

A
  1. Inhibit HMG-CoA Reductase
    - Cholesterol synthesis for CVD health
  2. Antioxidant
    - Quench free radicals, reduce oxidative stress
  3. Anti-inflammatory
  4. IN HUMANS: Reduce blood pressure
    - Biomarker for CVD health
    - Only sub-class of flavonoids to do so

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