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Food Chemistry > 11 Colorants > Flashcards

11 Colorants Flashcards

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1
Q

Part of colouring substances responsible for colour

A

chromophores

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2
Q

Any chemical, natural or synthetic, that imparts color

A

colorant

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3
Q

Natural substances in cell and tissues of plants that impart color

A

Pigments

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4
Q

Any substance that lend color refereing to colorant used in the textule industry OR “certified colors” that have been approved by the FDA as food-grade water soluble colorant

A

dye

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5
Q

Dyes extended on substratum and are oil dispersible

A

Lakes

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6
Q

Pigments found in animal and plant tissue

A
  1. Hemes (myoglobin/haemoglobin)
  2. Chlorophyll
  3. Carotenoids
  4. Flavonoids and other phenolic compounds (anthocyanins
  5. Betalaines
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7
Q

Protein portion of myoglobin

A

globin

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8
Q

Chromophore in myoglobin

A

Porphyrrin ring with Fe in the center, complexed with four tetrapyrole N (known as heme)

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9
Q

Meat colour is determined by

A
  1. Chemistry of myoglobins
  2. Ligands bound to heme
  3. Oxidation state
  4. State of globin protein
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10
Q

Oxygenation of myoglobin yields…
explain the changes in colour

A

Oxymyoglobin (MbO2-Fe2+)
Purple-red to bright red

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11
Q

Oxidation of myoglobin yields…
explain the changes in colour

A

Metmyoglobin (MetMb-Fe3+)
Purple-red to brownish-red

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12
Q

Oxidation of oxymyoglobin yields…
explain the changes in colour

A

Metmyoglobin (MetMb-Fe3+)
Bright red to brownish-red

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13
Q

Two sources of green discoloration

A
  1. Choleglobins
  2. Sulphomyoglobin
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14
Q

Mechanism of choleglobin synthesis

A

Reaction of hydrogen peroxide (H2O2) with ferrous/ferric site of heme

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15
Q

Mechanism of sulphomyoglobin synthesis

A

Presence of H2S and O2

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16
Q

Mechanism to stable pink colour in cured meat

A

Steps:
1. Myoglobin + Nitric oxide (NO) yields Nitrosylmyoglobin (bright red; unstable)
2. Heating of nitrosylmyoglobin denatues globin, forming nitric oxide myochemochromogen (nitrosylhemochrome), which is pink in colour

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17
Q

Formation of brown color from pink in cured meat

A

Exposure of nitrosohemachrome(Fe2+) to air and light, forming nitrosohemachrome(Fe3+)

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18
Q

Explain nitrite burn

A

Reaction of metmyoglobin and excess nitrite, yielding nitrimyoglobin (NMb), followed by heating in a reducing environment yielding nitrohemin, a green pigment

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19
Q

Structure of chlorophyll

A

Magnesium complexes derived from porphin, a fully unsaturated micro -cyclic structure containig four pyrrol rings linked by single bridging carbons

Substituted porphins are called porphyrin

The nucleus of chlorophylls are called PHORBIN and is formed by the addition of a fifth isocyclic ring to porphin

Also contains PHYTOL, a 20C monounsaturated isoprenoid alcohol

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20
Q

Difference between chrolorphyll a and chlorophyll b

A

Substituent in C1 ring A is CH3 for chlorophyll a and CHO for chlorophyll b

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21
Q

chlorophyll derivatives containing Mg

A

Phyllin

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22
Q

Magnesium free derivatives of chlorophyll

A

Pheophytin

Colour: olive green

(formed during reactions with head + acid)

23
Q

Products of reactions of chlorophyll resulting in hydrolysis of phytyl ester (phytol tail)

A

Chlorophyllides

Colour: bright green

(formed during blanching, which accelerates action of endogenous enzyme chlorophyllase)

24
Q

Products of reactions of chlorophyll resulting in the removal of Mg and hydrolysis of phytyl ester (phytol tail)

A

Pheophorbides

Colour: brown

(formed during treatment of chlorophyllide with heat + acid)

25
Q

Methods of preserving chlorophyll colour

A
  1. HTST
  2. Base addition
  3. Commercial application of metallocomplex
26
Q

Mechanism of chlorophyllin manufacture to retain chlorophyll colour

A

Addition of NaOH and CuSO4, in which the Cu oil replaces Mg and phytol tail is removed

27
Q

Mechanism of regreening in chlorophyll

A

Addition of Zn2+ with head and acid ro replace central Mg with Zn

28
Q

Basic structure of carotenoids

A

Backbone consists of isoprene units linked head-to-tail to create a symmetrical molecule

Comprised of two structural groups
1. hydrogen carbon carotenes
2. oxygenated carotenoids (xantophylls)

28
Q

Six types of carotenoids

A
  1. lutein
  2. crocetin
  3. alpha carotene
  4. beta carotene
  5. lycopene
  6. zeaxanthin
29
Q

Chromophore in carotenes

A

Conjugated double bonds

30
Q

How is the red colour in cooked shrimp brought about

A

red ASTAXANTHIN in shrimp exoskeleton is blue when complexed with proteins, which denature during cooking

31
Q

Carotenoids are susceptible to what chemical reaction?

A

Oxidation due to the large number of double bonds, causing colour loss and forming epoxides and carbonyl compounds

32
Q

Oxidative destruction of beta carotene is intensified in the presence of what

A

sulfite, metal ion and lipoxygenase enzyme

33
Q

Antioxidative properties of carotenoids

A
  • easily oxidised
  • quenchs singlet oxygen
  • photochemical protectos
  • isomerization from all trans to cis (decreasing activity to 13-53%)
34
Q

Characteristics of oxidation products of carotenoids

A

polymer, volatile, short chain, low Mr, water soluble compounds

35
Q

Difference between oxidation products of beta carotene due to chemical oxidation and light

A

Chemical: beta carotene-5,6-epoxide
Chemical: beta carotene-5,8-epoxide

36
Q

Effect of cooking and canning on beta carotene

A

forms neo beta carotene (38% vit C activity)

37
Q

Degradation products of beta carotene due to high temperature

A

toluene, ionine, 4-methyl-acetophenone

37
Q

Structure of anthocyanin

A

FLAVONOIDS comprise the skeleton of anthocyanins (C3-C6-C6) (A, C, B respectively)

substituents on ring A and B determine the colour

38
Q

Water soluble form of anthocyanins

A

Anthocyanin glycoside (anthocyanidin +sugar)

39
Q

Less water soluble form of anthocyanin

A

Anthocyanidin (rare in nature)

39
Q

Changes in anthocyanin forms and their respective colours

A

(A)
quinonoid: blue

(AH+)
flavylium: red

(B)
carbinol base: colorless

(C)
chalcone: colorless

40
Q

How to increase stability of anthocyanins

A
  • acidic conditions
  • decreased hydroxylation as aglycone substituent
  • increased methylation as aglycone substituent
  • less paelargonidin, cyanidin, or delphinidin aglycones
  • more petunidin or malvidin aglycones (blocks reactive hydroxyl groups)
  • increased glucosylation (as in monoglucosides and diglucosides)
  • high concentrations of sugars due to lower water activity
  • metal complex Ca, Fe, Al, Sn
41
Q

effect of SO2 on anthocyanins

A

Bleaching effect

Reversible: when preserved in 500-2000ppm SO2; can be restored by desulfuring (through washing) before further processing

Irreversible: attachment of SO2 at C4, formation of colorless complex

42
Q

Colour of quinones

A

Darker colours

fungi and lichens: yellow, orange, brown
sea lilies and coccid: red, blue, purplr

43
Q

Colour of xanthones

A

Yellow (e.g. in mangoes)

44
Q

Betalaines betacyanin are similar to what pigments?

A

Flavonoids (yellow) and anthocyanins (red)

45
Q

Types of betalaines

A
  1. Betacyanin (violet-red): betanin, betanidin
  2. Betaxanthins (yellow): vulgaxanthin
46
Q

Pigment found in sappan wood

A

brazillin (isoflavonoid)

47
Q

physical properties of brazillin

A

yellow crystal

becomes brownish-red when oxidised (brazilein, water soluble)
becomes red when exposed to sunlight

48
Q

changes in colour due to pH of brazilein

A

pH 2-5: yellow
pH 6-7: red
pH > 8: red-purple

49
Q

Degradation of brazilein affected by what factors

A

temperature, UV light, oxidator, reductor. metal

50
Q

Permitted natural colorants

A

caramel
beta carotene
chlorophyll
curcumin

51
Q

Permitted synthetic colorants

A

Brilliant blue
Tartrazine
Indogotine
Sunset yellow
Erythrosine
Allura red
Orange B
Citrus red no.2

Food Chemistry (5 decks)

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