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Food Chemistry

Food Chemistry . Chapter 17 in Green / Damjii. Homework. F.4: Colour. Read F4 – Colour - pp. 481-486 Do Qs 24-33 on p 491-492. F.4.1: Distinguish between a dye and a pigment. DYE Colouring materials that are synthetic or from other natural sources Food dye =

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Food Chemistry

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  1. Food Chemistry Chapter 17 in Green / Damjii

  2. Homework F.4: Colour • Read F4 – Colour - pp. 481-486 • Do Qs 24-33 • on p 491-492

  3. F.4.1: Distinguish between a dye and a pigment • 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

  4. F.4.1: Distinguish between a dye and a pigment • 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.

  7. anthocyanins

  8. anthocyanins

  9. carotenoids

  10. carotenoids

  11. carotenoids

  12. chlorophyll

  13. heme

  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 caramelisationthat 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 • aldehydegroup (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 • Cn(H2O)n  n C + n H2O

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

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