Homework Read F4 – Colour - pp. 481-486 Do Qs 24-33 on p 491-492 F.4: Colour
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
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
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
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)
anthocyanins SourceColor(s) Anthocyanins [flavanones] berries; beetroot ; red cabbage; flowers [red grapes; berries] Red – pink – purple – blue [red]
chlorophyll SourceColor(s) Chlorophyllgreen plants; green vegetablesgreen
heme SourceColor(s) hemered blood cells of higher animals (meat) Red (red w/ oxygen; purple-red w/o oxygen; brown-red when oxidized)
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.
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.
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.
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.
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.
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.
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.
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
Maillard Reaction Grilling meat, toasting bread, malting barley, making fudge – (also self-tanning treatments – imagine that !) Occur at temperatures > 140°C
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
Caramelization Occurs in foods with high carbohydrate concentration – Sugars
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
Caramelization Rate varies depending on sugar – Fructose (in fruits) is easiest to caramelize Extreme pH (high and low) promotes caramelization