CHEM215 Lecture Notes - Lecture 19: Food Additive, Phytol, Olive Oil
Lecture 19 – Food Additives 2
Chlorophyll:
• Composed of two molecules:
-Phytyl chain
-Porphyrin
• The phytyl chain of chlorophyll is a long hydrocarbon chain that makes it
insoluble in water.
• Porphorin has has a ring system that has many conjugated double bonds and a
magnesium atom at the centre —> this is what gives the colour.
• These two molecules are attached by an ester linkage.
• There are two types of chlorophyll molecules —> chlorophyll A and chlorophyll B
Compounds of chlorophyll produced by reactions:
• Pheophytin a and b are formed when the Mg2+ is lost through heat and acid —>
olive oil
• Chlorophyllide a and b are formed by the action of the enzyme chlorophyllose
that cleaves the phytol group —> produces a bright green colour
• Pheophorbide a and b —> grey/brwon colour of canned green beans and brined
cucumber pickles due to loss of both photos and Mg2+
Adding colourants to food:
Why add colours to food?
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Lecture 19 – Food Additives 2
• Make it more visually appealing —> marketing
• Make it loos how consumers perceive it should look. Ie a cherry ripe should look
red inside because it is meant to be cherries.
Food additives are controlled by legislation:
• FSANZ governs what additives are allowed to be used.
Colouring food additives:
Carminic acid:
• red colouring substance that is obtained from coccid insects (ie cochineal). It is a
pale yellow colour that competes readily with tin, aluminium and other metals
into brilliant red pigments. This colour can also be synthetically produced by the
dye alizarin yellow.
• The coloured complexes are relatively stable under food processing conditions but
are easily bleached by sulfur dioxide —> ie cannot use sulfur dioxide as the
preservative agent with foods containing carminic acid.
• Need to be able to recognise the structure of carminic acid
Anthocyanin:
• Widespread throughout nature
• Use of colouring foods and drinks is limited due to:
-sensitivity to bleaching by sulfur dioxide
-limited colouring capacity at pH values above 3.5
• The lack of groups present on the 4th carbon in the anthocyanin molecule in some
naturally occuring products (ie grape skin extract) contributes to its instability and
its easy degradation by sulfur dioxide and high pHs.
• Vitisins (Vitasin A & B, vitisidin A & B) are a new class of anthocyanin that have
recently been discovered. They are found in red wines and are thought to form as
the wine ages and matures - they are not naturally present in the grapes. All four
of these pigments have substituents in their 4th position so are more stable.
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