1. Chapter 17 in Green / Damjii
Food Chemistry
Chapter 17 in Green / Damjii

2. F.4: Colour Homework Read F4 – Colour - pp. 481-486 Do Qs 24-33
on p

3. F.4.1: Distinguish between a dye and a pigment
Colouring materials that are synthetic or from other natural sources
Food dye =
food grade, water soluble colour
Natural ex = saffron, paprika, caramel
Artificial = tartrazine (see right)
aka Yellow 5

4. F.4.1: Distinguish between a dye and a pigment
Colouring materials naturally present in cells of plants and animals (… in foods)
Examples:
Anthocyanins
Carotenoids
Chlorophyll
Heme
melanin, hemoglobin, myoglobin

5. F.4.2: Explain the occurrence of colour in naturally occurring pigments
COLOUR (aka COLOR) is due to …
absorption of certain frequencies of visible light
by the extensive delocalized pi bonds
reflection of other frequencies of light that stimulate the retina in the eye
EX – Spinach
red and blue light are absorbed
green light is reflected

6. F.4.3: Describe the range of colours and sources of the naturally occurring pigments anthocyanins, carotenoids, chlorophyll, and heme.
Source
Color(s)
Anthocyanins
[flavanones]
berries; beetroot ; red cabbage; flowers
[red grapes; berries]
Red – pink – purple – blue
[red]
Carotenoids
[Astaxanthin]
All living things; algae; carrots, bananas ; tomatoes; saffron
[lobsters; crabs; salmon]
Yellow – orange – red
Chlorophyll
green plants; green vegetables
green
heme
red blood cells of higher animals (meat)
Red
(red w/ oxygen; purple-red w/o oxygen; brown-red when oxidized)

7. anthocyanins Anthocyanins [flavanones]
Source
Color(s)
Anthocyanins
[flavanones]
berries; beetroot ; red cabbage; flowers
[red grapes; berries]
Red – pink – purple – blue
[red]

8. anthocyanins

9. carotenoids Carotenoids [Astaxanthin]
Source
Color(s)
Carotenoids
[Astaxanthin]
All living things; algae; carrots, bananas ; tomatoes; saffron
[lobsters; crabs; salmon]
Yellow – orange – red
[red]

10. carotenoids Carotenoids [Astaxanthin]
Source
Color(s)
Carotenoids
[Astaxanthin]
All living things; algae; carrots, bananas ; tomatoes; saffron
[lobsters; crabs; salmon]
Yellow – orange – red
[red]

11. carotenoids

12. chlorophyll Chlorophyll green plants; green vegetables green Source
Color(s)
Chlorophyll
green plants; green vegetables
green

13. heme heme red blood cells of higher animals (meat) Red
Source
Color(s)
heme
red blood cells of higher animals (meat)
Red
(red w/ oxygen; purple-red w/o oxygen; brown-red when oxidized)

14. F.10.1: Compare the similarities and differences in the structures of the natural pigments: anthocyanins, carotenoids, chlorophyll and heme.
Similarities:
all have extensive delocalized pi bonds
most have ring systems – some fused
many have –OH groups attached

15. F.10.1: Compare the similarities and differences in the structures of the natural pigments: anthocyanins, carotenoids, chlorophyll and heme.
Differences:
Overall shape
Anthocyanins, Chlorophyll, heme – more compact
Carotenoids – long and stringy
some contain N and are capable of forming metal complex ions
Chlorophyll (Mg 2+)
Heme (Fe 2+)

16. F.10.2: Explain why anthocyanins, carotenoids, chlorophyll and heme form colored compounds while many other organic molecules are colorless.
COLOUR (aka COLOR) is due to …
absorption of certain frequencies of visible light
by the extensive delocalized pi bonds
(alternating single and double bonds)
As delocalization increases, the energy split between the bonding and anti-bonding pi orbitals becomes smaller, shifting the absorbed light into the visible region.
reflection of other frequencies of light that stimulate the retina in the eye

17. F.10.3: Deduce whether anthocyanins and carotenoids are water- or fat-soluble from their structures.
Anthocyanins – water soluble
Multiple –OH groups
can hydrogen bond with water
Carotenoids – fat soluble
Long hydrocarbon chains
Insufficient –OH groups to overcome HC chain

18. F.4.4: Describe the factors that affect the color stability of anthocyanins, carotenoids, chlorophyll and heme. pH
impacts anthocyanins & chlorophyll (H+ replaces magnesium)
Formation of complex ions
impacts anthocyanins (cooking in metal pans),

19. F.4.4: Describe the factors that affect the color stability of anthocyanins, carotenoids, chlorophyll and heme.
Temperature
can impact all groups – particularly denaturing proteins
Oxidation
Impact carotenoids (saturation of chain); heme (binding to oxygen and oxidation of iron)

20. F.4.5: Discuss the safety issues associated with the use of synthetic colorants in food.
Concerns:
Synthetic dyes are biochemically active
Can negatively impact health
toxicity is easy to prove
chronic health effects are difficult to determine
Special concern about carcinogenic effects
Most are NOT typically used in foods
Standards vary from country to country
Malachite green and sudan red are generally banned

21. F.4.6: Compare the two processes of non-enzymatic browning (Maillard reaction) and caramelisation that cause the browning of food.
NOTE: Browning usually involves BOTH processes… except for those foods that do not have amino acids or proteins
sugar  toffee
sugar  crème brulee

22. Occur at temperatures > 140°C
Maillard Reaction
Grilling meat, toasting bread, malting barley, making fudge
(also self-tanning treatments – imagine that !)
Occur at temperatures > 140°C

23. aldehyde group (from sugar) reacts with
Maillard Reaction
aldehyde group (from sugar) reacts with
amino group (from AA, peptide, or protein)
Rate depends on particular amino acids used
Lysine is more reactive
(found in milk – so it browns readily – fudge)
Cysteine is less reactive
MANY products
smaller molecules = aromas & flavors
initial products then polymerize to form brown pigments
melanoidins

24. Occurs in foods with high carbohydrate concentration
Caramelization
Occurs in foods with high carbohydrate concentration
Sugars

25. Caramelization When heated…
Carbohydrate molecules dehydrate and form polymers
many products
polymers have brownish color
With continued heating…
form carbon and water
Cn(H2O)n  n C + n H2O

26. Rate varies depending on sugar
Caramelization
Rate varies depending on sugar
Fructose (in fruits) is easiest to caramelize
Extreme pH (high and low) promotes caramelization