1. POLYPHENOL COLORATION
OBJECTIVES
1. Polyphenols – classification and representatives;
2. Non-enzymatic polyphenol coloration;
3. Enzymatic polyphenol coloration;

2. POLYPHENOL COLORATION1
Polyphenol coloration (non-enzymatic) – mostly due to complexation with metal cations, changes of the рН, disintegration or formation of some pigments during food processing.
Polyphenol coloration (enzymatic) – due to action of polyphenol oxidases (PPO). !
Type of polyphenols
Structure
Type С6
Simple phenols
С6 – С1
Phenolic acids and aldehydes
С6 – С2
Derivatives of phenylacetic acid and acetophenone
С6 – С3
Derivatives of cinnamic acid
Coumarins and isocoumarins
С6 – С3 – С6
Flavonoids
С6–С1–С6;
С6–С2–С6
Benzophenons, xanthons and stilbenes
С6, С10, С14
Quinones
Dimers and oligomers
Lignans
Polymer
Lignin
Tannins

3. POLYPHENOL COLORATION Phenolic acids and aldehydes2
Simple phenols:
resorcinol
pyrogallol
Phenolic acids and aldehydes
р-hydroxy-benzoic
protocatehuic
vanillic
salicylic
gallic
vanillin

4. POLYPHENOL COLORATION Derivatives of cinnamic acid3
Derivatives of cinnamic acid
5-hydroxy-ferulic
cinnamic
caffeic
sinapic
р-coumaric
ferulic
Stilbenes – resveratrol

5. POLYPHENOL COLORATION4
Lignans and lignin
coniferyl alcohol
р-coumaril alcohol
Sinapyl alcohol
Oligomeric and polymeric structures

6. POLYPHENOL COLORATION5
Flavonoids
General structure: γ-benzopyron linked to benzene ring
flavonoids
isoflavonoids
neoflavonoids

7. POLYPHENOL COLORATION6
Flavonoids
Depending from the degree of saturation of the heterocycle (O-containing ring) the
flavonoids could be:
1). Derivatives of phenylbenzo-γ-pyron (flavons, flavonols, flavanols and flavanonols)
2). Derivatives of phenylbenzo-γ-pyran (flavan-3-ols, anthocyanindins and flavan-3,4-diols)
Flavons
luteolin
apigenin

8. POLYPHENOL COLORATION7
Flavonoids
Flavonols
Flavonols beside the characteristic for the flavons keto-groups and C=C bond have OH group at 3rd place. Flavonols are much more distributed in nature than flavons.
kaempferol
quercetin
myricetin

9. POLYPHENOL COLORATION8
Flavonoids
Flavanons
The flavanons have keto-group but didn’t have C=C bond in the heterocycle
naringenin
Flavanonols
taxifolin

10. POLYPHENOL COLORATION9
Flavonoids
Flavan-3-ols (cathehins)
The name cathehin comes from catechu, which is the tannic juice or boiled extract of Mimosa catechu (Acacia catechu L.f). The cathehins could form esters with gallic acid – esterification of the OH group at 3’ position
cathehin
gallocathehin

11. POLYPHENOL COLORATION10
Flavonoids
Flavan-3,4-diols (leucoanthocyanidins)
The leucoanthocyanidins are synthesized from flavanonols by reduction of the keto-group. They are found in the wood where they play a role in forming the condensed tannins.
leucodelphinidin
leucocyanidin

12. POLYPHENOL COLORATION!
POLYPHENOL COLORATION 11
Flavonoids
Anthocyanidins
In the nature the most often found are 6 anthocyanidins which after glycosylation give a great variety of anthocyanins (glycosides of anthocyanidins). They have pronounced P-vitamin activity, lower the fragility and permeability of the capillary. They have anti inflammatory, hypotonic and collagen-stabilizing action. The anthocyanins intake is beneficial for the capillary system and improvement of the vision. They play important role in the collagen crosslinking and inhibit its enzymatic degradation during inflammatory processes. Anthocyanins are applied successfully for prophylaxis and treatment of glaucoma and other ophthalmic diseases. In model systems extracts rich in anthocyanins show cardio-protective effect and inhibit the growth of cancer cells.
Name R1 R2
Delphinidin OH
Petunidin
OCH3 H
Cyanidin
Pelargonidin
Peonidin
Malvidin

13. POLYPHENOL COLORATION12
Complexation and color formation
The flavonoids – found in almost all fruits and vegetables. Complexation with metals like Fe3+, Ca2+, Al3+, Sn2+, Cu2+ are the reason for coloration.
Fe3+ - the complexes with tannins are used for tannins measurements in beers.
The observed coloration of potatoes after boiling – complexation of Fe3+ with o-phenols.
Sometimes coloration of processed cauliflower – complexes of Fe2+ kaempferol and quercetin. The canned cauliflower could give yellow colored complexes with tin.
Formation of pink coloration (pinking) of pears and peaches after thermal treatments (and subsequent slow cooling) – due to formation of cyanidin complexes with copper, iron and zinc.
More at CRC Handbook of Food Additives, Ed. Thomas E. Furia (2nd edition), CRC Press 1972 NY. (pages )

14. POLYPHENOL COLORATION13
Complexation and color formation
Coloration of canned asparagus shoots (dark-greenish to black) – complexes of rutin (quercetin-3-O-rutinoside) with Fe2+ (EDTA or presence of Sn2+ - eliminate the coloration problems). Generally use of sequestrants is the solution for complexation of polyphenols with metals and obtaining of unusual coloration or discoloration
The formation of the color of ripe olives – dark-brown to black is due to formation of oxidative products of flavonoids (luteolin 7-glycoside). Other compounds responsible: peonidin-3-glucoside, cyanidin-3-rhamnoglucoside (acylated with caffeic acide), hydroxytyrosol, vanillic acid, caffeic acid, p-coumaric acid etc.

15. POLYPHENOL COLORATION14
Changes of the color with change of the pH – example: anthocyanins
Anthocyanins of red cabbage: left to right – increase of the рН

16. POLYPHENOL COLORATION15
Anthocyanin structures
Flavylium salt (red)
Quinonoidal base (blue-dark green)
Chalcone (colorless)
Pseudobase or carbinol (colorless)

17. POLYPHENOL COLORATION16
Stabilization of strawberry beverages with addition of polyphenols.
Plamen Mollov, Kiril Mihalev, Vasil Shikov, Nikolina Yoncheva, Vasil Karagyozov, Colour stability improvement of strawberry beverage by fortification with polyphenolic copigments naturally occurring in rose petals, Innovative Food Science & Emerging Technologies, 8(3), 2007, 318–321.

18. POLYPHENOL COLORATION17
Formation of complexes with phenolic compounds - stabilization
Molecular complexes between anthocyanin and a polyhydroxyflavone sulfonate –
Food chemistry, Fennema

19. POLYPHENOL COLORATION18
Degradation of antocyanins
Polymeric brown
degradation products
Glycoside bonds and presence of sugars – stabilizing effect on anthocyanins; but the products formed (cyclic aldehydes, carbonyls) when Maillard reaction takes place lead to condensation reaction with anthocyanins and formation of brown colored products

20. POLYPHENOL COLORATION19
Interaction of phenolic compounds with 5-HMF (or HMF)

21. ENZYMATIC BROWNING 20

22. ENZYMATIC BROWNING 21 1. Significance
- Formation of humus in the soil;
- Biosynthesis of melanins in the organisms – pigmentation, defense from the UV-rays;
- Formation of color in the tea leaves, tobacco, cocoa; processes of ripening of dates, figs, raisins etc.;
- Protective mechanism of the fruit and vegetables;
- Participate in the redox reactions – defence mechanism;
Melanin in the melanocyte

23. ENZYMATIC BROWNING 22 2. Mechanism of action Polyphenol oxidase (РРО)
Substrates of the reaction – monophenols, L-tyrosine, hydroxy-derivatives of cinnamic acid (p-coumaric, caffeic, ferulic, chlorogenic acid)
Catechol oxidase – catalyzes oxidation of o-diphenols to quinones.

24. ENZYMATIC BROWNING 23
2. Mechanism of action

25. ENZYMATIC BROWNING 24
2. Mechanism of action – obtaining of melanins from L-tyrosine

26. ENZYMATIC BROWNING 25 3. Types of melanins
3.1. Alomelanins – plant melanins (catechol derived)
catechol
Sample structure of catechol melanins

27. ENZYMATIC BROWNING 26 3. Types of melanins
3.2. Eumelanins – animal type (tyrosine derived, indolic structure);
dark-brown color.
Tyrosine → DOPA → dopaquinone
Dopachrome
Leucodopachrome
Sample structure of
eumelanins

28. ENZYMATIC BROWNING 27 3. Types of melanins
3.3. Pheomelanins – animal type (tyrosine and cysteine derived,
indolic structure); red-brown color.
cysteine
L-DOPA
Sample structure of
pheomelanins

29. ! ENZYMATIC BROWNING 28 4. Processes of enzymatic browning desired
- fermentation of tea leaves;
- fermentation of cocoa beans;
- obtaining of sake;
- obtaining of soy sauce.
undesirable
- discoloration of wounded tissues – as a result of microbial attack, wounding during picking, transportation, storage;
- treatment of the raw materials – peeling, trimming, milling, etc.
- chilling and freezing processes;
- drying processes;
- processing of crustaceans.
inhibition
- Tropolone ( grape polyphenol oxidase inhibitor);
- Potassium metabisulfite, K2S2O5;
- Potassium dithionite or potassium hydrosulfite, K2S2O4;