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International Baccalaureate Chemistry Higher level programme class notes for the Option F chapter for food dyes and pigments
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Dyes and pigments
Why are colours important for food?-atractive-indication of ripeness-indication of toxicity\
dyes: synthetic compounds which are food grade water soluble substances and added to improve colours
-coloured because-absorbs light in the visible region of the electromagnetic spectrum, transmit remaining light-appears as complementary colour
poppies are red: absorbs light at 375nm and 530nm-375 nmneed to know approximate values-530nm blue green region of the visible light spectrum-complementary colour to green blue is red
Pigments3 main types: anthicyanins C6-most widely occurring in plantspink red purple blue in fruits and vegetables-cranberries, blueberries, strawberries, raspberries-conjugated double carbon bonds-3 rings 6-3-6 structurecarotenoids-widespread, major produced by algaeprecursor for VA-similarly: conjugated double bondsREASON DOUBLE BONDS CAN EMIT COLOUR-more conjugation, more resonance, more energy
chlorophyllheme-red, haemoglobin: from animals
cooking lobster=> not reversible: some changechemical stability
oxidation=oxidised pigment moleules
pineapple-discolouratuion due to formation of complex with FE3+
delocalised e-s on the ring
carotenoid-extremely reactive allylic bonds due to high hnumber of unsaturated carbon carbon double bondsheating: natural trans isomer rearranges to cis isomer
chlorophjyllstability: heat and phMg2+ ions (stable complex)Baking soda-extremely green (9)Chlorophyll stableOlive greenVinegar –light colour(3)Yellowish brown colourh h Chlorophyll: degrade during heating-no longer can form coordinate bonds w/ magnesium ions-myoglobin+heme is hemogkobinbasis: oxygen can form reversible dative bonds with iron ionsoxyhemoglobin: red in colourautooxidation
foods containing lysine browns readilyheating foods with high carbohydrate content
mr szeto: buffet toniteYH:fraid-cant see toes?
Mr szeto:hes just jealous
Amino acids -sugar only