Colour-lec 2

Question 1

What is the difference between pigment and dye?

Answer 1

Pigment: natural substance in cells/tissues that give colour
Dye: substance that lends colour to materials

Question 2

What are Lakes in the context of food colour?

Answer 2

Insoluble pigments formed by binding dyes to a base material, ideal for fat-based or powdered food systems.

Question 3

What is Fluorescence?

Answer 3

The emission of visible light from an excited molecule after absorbing energy
- electronic transitions in molecules correspond to the absorption of light

Question 4

What are Chromophores? how are they found?

Answer 4

Parts of molecules responsible for absorbing light and reflecting a colour

They produce coloured compounds as a result of:
1) conjugated double bonds
-carotenoids & anthocyanins
2) metal-coordinated porphorin structures
-chlorophyll & myoglobin

Question 5

What happens when white light hits a coloured substance?

Answer 5

1) Partial absorption and reflection occur, allowing us to see the colour of the reflected light.
OR
2) reflection of the complementary colour to a single colour that is absorbed

Question 6

why is colour assessment done?

Answer 6

1) determine how colour changes with changes in ingredients
2) determine colour change when storage or processing is changed
3) Quality control to ensure consistency
4) Quality control to determin conformance to final product specification

Question 7

How do opaque, translucent and transparent foods differ? provide some examples

Answer 7

Opaque: wholly reflected light
-fruit,crackers, flour, cheese

Translucent: partially reflected / transmitted light
-fruit juices, jams, custard

Transparent
- clear juices, wines, jellies, veg oil

Question 8

What are Artificial food colours? why are they used?

Answer 8

Synthetic chemicals engineered to provide vivid, stable colours in processed foods.

Question 9

What is the structure of artificial colours?

Answer 9

1) extensive conjugateion for wide variety of colours
2) salt for solubility
- a chromophore found in many synthetic food dyes, characterized by the -N=N- structure

Question 10

What factors affect dye stability? how does the stability of natural vs synthetic dyes differ?

Answer 10

• pH * Light exposure * Heat * Interactions with other ingredients
  -synthetic dyes are very stable and soluble compounds, increasing shelf life of the product

Question 11

What is Curcumin?

Answer 11

A yellow-orange polyphenolic compound found in turmeric.

Question 12

What are Carotenoids?

Answer 12

Pigments split into carotenes and xanthophylls, absorbing in the blue-violet spectrum (reflecting orange-yellow)

Question 13

What is the all-trans form of β-Carotene?

Answer 13

The most stable and commonly found isomer of β-Carotene.

Question 14

Why does the change in pigments occur in leaves? what pigments are present when? (chlorophyll, anthocyanin, carotenoid, tannins)

Answer 14

Green (chlorophyll): masks other pigments with high levels of light exposure
Anthocyanin (red): increase with increased sugar levels
Carotenoid (orange/yellow): increase as anthocyanin levels decrease
Tannins (brown): reponsible for oak leaf colour

Question 15

What are examples of natural pigments? what colour are they? where are they found?

Answer 15

Heme (red): meat
Cholorophyll (blue-green): lettuce
Carotenoids (yellow-orange): carrot
Flavonoid/phenolic (orange,red,blue): berries, apple
Betalilns (purple-red): beets, pear

Question 16

what is the basic structure of anthocyanins?

Answer 16

flavylium ion

Question 17

What does the visible absorption spectrum of β-Carotene indicate?

Answer 17

Each isomer absorbs light at slightly different wavelengths due to alterations in the conjugated double bond system.

Question 18

What are betalains?

Answer 18

Yellow / red water soluble pigments from beets
-Used as natural food colorants and for their antioxidant properties

Question 19

How do betalains differ from carotenoids?

Answer 19

Betalains are water-soluble, while carotenoids are not.

Question 20

What are examples of tetrapyrroles?

Answer 20

• Porphyrins (e.g., heme, chlorophyll)
• Bind metal ions at the center (e.g., Fe²⁺ in heme, Mg²⁺ in chlorophyll).

Question 21

What is the structure of chlorophyll? what are its attributes?

Answer 21

Composed of a porphyrin ring with Mg²⁺ at the center and a phytol tail
-soluble in moderately polar solvents

Question 22

What is the chlorophyll a/b ratio in green plants?

Answer 22

Approximately 3:1.

Question 23

What factors impact chlorophyll degradation?

Answer 23

• Heat
• pH
• Enzyme chlorophyllase.

Question 24

What is pheophytin? what colour is produced? what happens with further oxidation and loss of phytol?

Answer 24

Loss of Mg²⁺ leads to an olive green color
-further oxidation produces pyropheophorbide

Question 25

What is pyropheophytin?

Answer 25

Further breakdown of pheophytin due to heat, resulting in a dull brown color.

Question 26

What is the Blue/Red absorption ratio for chlorophyll a? what about pheophytin a?

Answer 26

1.3 2.1 -loss of Mg -> increased blue absorption

Question 27

What happens when Mg(II) in chlorophyll is replaced?

Answer 27

Dull colors form, and substitutions with Cu²⁺ or Zn²⁺ can create bright green stable complexes.

Question 28

what do you expect of chlorophyll content when spinach is blanched, canned, fresh or frozen?

Answer 28

Blanched: chlorophyll retained- generation of a' and b' isomers Fresh: high levels of chlorophyll a/b (vibrant green) Frozen: Chl a/b still present- generation of pheophytin a may cause colour change Canned: no Chl a/b; high levels of Phe a /b and pyro a/b (olive brown/dull brown) - loss of vibrant green

Question 29

What is nitrosomyoglobin?

Answer 29

Formed when nitrites convert Mb to Mb-NO, leading to stabilization and a bright pink color.

Question 29

What are the different states of myoglobin?

Answer 29

* Deoxymyoglobin (purple-red) -Fe2+, no O2 bound (myoglobin) * Oxymyoglobin (bright red) -Fe2+ with O2 bound * Metmyoglobin (brown) -Fe3+, H2O bound