Presentation is loading. Please wait.

Presentation is loading. Please wait.

Food Chemistry Chapter 17 in Green / Damjii. Homework Read F4 – Colour - pp. 481-486 Do Qs 24-33 on p 491-492 F.4: Colour.

Similar presentations


Presentation on theme: "Food Chemistry Chapter 17 in Green / Damjii. Homework Read F4 – Colour - pp. 481-486 Do Qs 24-33 on p 491-492 F.4: Colour."— Presentation transcript:

1 Food Chemistry Chapter 17 in Green / Damjii

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

3 DYE – 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 F.4.1: Distinguish between a dye and a pigment

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

5 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 F.4.2: Explain the occurrence of colour in naturally occurring pigments

6 F.4.3: Describe the range of colours and sources of the naturally occurring pigments anthocyanins, carotenoids, chlorophyll, and heme. SourceColor(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 [red] Chlorophyllgreen plants; green vegetablesgreen hemered blood cells of higher animals (meat) Red (red w/ oxygen; purple-red w/o oxygen; brown-red when oxidized)

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

8 anthocyanins

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

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

11 carotenoids

12 chlorophyll SourceColor(s) Chlorophyllgreen plants; green vegetablesgreen

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

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

15 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+ ) F.10.1: Compare the similarities and differences in the structures of the natural pigments: anthocyanins, carotenoids, chlorophyll and heme.

16 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 F.10.2: Explain why anthocyanins, carotenoids, chlorophyll and heme form colored compounds while many other organic molecules are colorless.

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

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

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

20 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 F.4.5: Discuss the safety issues associated with the use of synthetic colorants in food.

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

23 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 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 C n (H 2 O)n  n C + n H 2 O

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


Download ppt "Food Chemistry Chapter 17 in Green / Damjii. Homework Read F4 – Colour - pp. 481-486 Do Qs 24-33 on p 491-492 F.4: Colour."

Similar presentations


Ads by Google