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Food Chemistry > 11 Colorants > Flashcards

11 Colorants Flashcards

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
Methods of preserving chlorophyll colour
1. HTST 2. Base addition 3. Commercial application of metallocomplex
26
Mechanism of chlorophyllin manufacture to retain chlorophyll colour
Addition of NaOH and CuSO4, in which the Cu oil replaces Mg and phytol tail is removed
27
Mechanism of regreening in chlorophyll
Addition of Zn2+ with head and acid ro replace central Mg with Zn
28
Basic structure of carotenoids
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
Six types of carotenoids
1. lutein 2. crocetin 3. alpha carotene 4. beta carotene 5. lycopene 6. zeaxanthin
29
Chromophore in carotenes
Conjugated double bonds
30
How is the red colour in cooked shrimp brought about
red ASTAXANTHIN in shrimp exoskeleton is blue when complexed with proteins, which denature during cooking
31
Carotenoids are susceptible to what chemical reaction?
Oxidation due to the large number of double bonds, causing colour loss and forming epoxides and carbonyl compounds
32
Oxidative destruction of beta carotene is intensified in the presence of what
sulfite, metal ion and lipoxygenase enzyme
33
Antioxidative properties of carotenoids
- easily oxidised - quenchs singlet oxygen - photochemical protectos - isomerization from all trans to cis (decreasing activity to 13-53%)
34
Characteristics of oxidation products of carotenoids
polymer, volatile, short chain, low Mr, water soluble compounds
35
Difference between oxidation products of beta carotene due to chemical oxidation and light
Chemical: beta carotene-5,6-epoxide Chemical: beta carotene-5,8-epoxide
36
Effect of cooking and canning on beta carotene
forms neo beta carotene (38% vit C activity)
37
Degradation products of beta carotene due to high temperature
toluene, ionine, 4-methyl-acetophenone
37
Structure of anthocyanin
FLAVONOIDS comprise the skeleton of anthocyanins (C3-C6-C6) (A, C, B respectively) substituents on ring A and B determine the colour
38
Water soluble form of anthocyanins
Anthocyanin glycoside (anthocyanidin +sugar)
39
Less water soluble form of anthocyanin
Anthocyanidin (rare in nature)
39
Changes in anthocyanin forms and their respective colours
(A) quinonoid: blue (AH+) flavylium: red (B) carbinol base: colorless (C) chalcone: colorless
40
How to increase stability of anthocyanins
- 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
effect of SO2 on anthocyanins
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
Colour of quinones
Darker colours fungi and lichens: yellow, orange, brown sea lilies and coccid: red, blue, purplr
43
Colour of xanthones
Yellow (e.g. in mangoes)
44
Betalaines betacyanin are similar to what pigments?
Flavonoids (yellow) and anthocyanins (red)
45
Types of betalaines
1. Betacyanin (violet-red): betanin, betanidin 2. Betaxanthins (yellow): vulgaxanthin
46
Pigment found in sappan wood
brazillin (isoflavonoid)
47
physical properties of brazillin
yellow crystal becomes brownish-red when oxidised (brazilein, water soluble) becomes red when exposed to sunlight
48
changes in colour due to pH of brazilein
pH 2-5: yellow pH 6-7: red pH > 8: red-purple
49
Degradation of brazilein affected by what factors
temperature, UV light, oxidator, reductor. metal
50
Permitted natural colorants
caramel beta carotene chlorophyll curcumin
51
Permitted synthetic colorants
Brilliant blue Tartrazine Indogotine Sunset yellow Erythrosine Allura red Orange B Citrus red no.2

Food Chemistry (5 decks)

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