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NUTR 3330 (14)


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NUTR 3330
Alison Duncan

FLAVONOIDS WHAT ARE THEY - the stars of phytochemicals - when first discovered, called ‘Vitamin-P’, P = pigment. Vitamin concept later dismissed - subclass of polyphenols - sub-group of low molecular weight polyphenolic substances o star of plant polyphenols o most common group of polyphenols o research on possible nutritional role of polyphenols focused on flavonoids - ubiquitos; present in most plants o concentrated in seeds, fruit skin or peel, bark, flowers STRUCTURE - common structure of diphenylpropanes (C6-C3-C6) o 2 aromatic rings linked through 3 carbons - Basic flavonoid structure: A ring from acetate pathway B ring from Shikimate pathway  Both A & B rings have OH groups attached (→) C ring determines the major class of flavonoid FUNCTION - shown to enhance Vitamin C function – improves absorption and protects it from oxidation o beginning evidence supporting potent antioxidant effects CLASSIFICATION - over 5000 have been discovered - 6 major subclasses –based on C ring o (1) Flavones o (2) Flavonols o (3) Flavanones o (4) Flavanols o (5) anthocyanidins o isoflavones DISTRIBUTION IN PLANTS - same concept as polyphnols - mainly in leaves, flowers and outer parts of the plant (skin, peel) - decreased concentrations toward the central core - only trace amounts found in subterraneous parts of plant o some exceptions – onions, garlic FOOD SOURCES - widely distributed in foods and beverages of plant origin o fruit, vegetables, tea, cocoa, wine FLAVONOIDS FLAVONOID INTAKE - similar concepts to polyphenols - challenges in determining dietary intake relating to determination of flavonoid composition o Content variation – species & genetic variations, light, environmental conditions, germination, degree of ripeness, processing and storage  e.g. cherry tomatoes contain 6x more quercitin (flavonoid)/g fresh weight than normal size varieties – maybe because we eat more skin with cherry tomatoes as opposed to larger tomatoes o Analytical methodology  lack of standardization  information in the literature is often contradictory - determining intake – analytical studies not always correct - flavonols and flavones are the most measured FLAVONOID GLYCOSIDES - flavonoids typically attached/conjugated to carbohydrate moieties in food - Terminology... sugar molecule? o YES = flavonoid glycoside o NO = flavonoid aglycone - majority of flavonoids appear in plants as glycosides Purposes of flavonoid glycosylation - increase polarity - necessary for storage in plant vacuoles - most common sugar residue: o glucose o others include: arabinose, galactose, xylose, other less common carbohydrate substitutions BIOAVAILABILITY - initially thought to be negligible since bound to glycosides - not the case! - present in blood and urine - flavonoids are absorbed and reach concentrations of varying magnitudes in our biological fluids BIOLOGICAL EFFECTS 1. Antioxidant - direct free radical scavengers - protect vitamin E
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