1. Pigments in fruits and vegetables
Fat soluble/ lipophilic pigments
Water soluble/ lipophobic pigments
Chlorophyll
Anthocyanin (red/blue/purple)
Carotenoids (red, orange and yellow)
Flavones & flavanols (yellow)
Flavanals etc.

2. Classification based on chemical structure and property
Tetrapyrrole = Chlorophyll
Isoprenoid derivatives =Carotenoids
Benzopyran = Anthocyanin and flavonoids

3. CHLOROPHYLL Found in green leaves & unripe fruits
Required for photosynthesis
Present in chloroplastids/chromaplastids
2 types of chlorophyll
Chlorophyll a (blue green)
Chlorophyll b (dull green-yellow)

4. Structure
Tetrapyrrole pigments consists of four 5-membered pyrrole group joined together to form basic porphyrin ring
A Mg atom coordinated in the centre and chelate by the 4 N of the pyrrole groups.
Chlorophyll is metalloporphyrin
A phytol group is attached at position 7. It is responsible for the solubility of the chlorophylls in organic fat solvents.

6. Degradation of chlorophyll
3 major reaction
Loss of Mg
Removal of phytol
Oxidation & ring splitting (not in the syllabus)
Chlorophyll molecules are sensitive to acid degradation, particularly carboxylic acids present in fruits and vege eg. Citric acid and malic acid.
In fresh raw tissues, chlorophyll pigments and carboxylic acid are kept separate.
Protected by lipoprotein in the chloroplasts
Carboxylic acid do not have any effect on chlorophyll

7. Treatments such as cutting, blending, heat treatment can alter the permeability of cell membrane, allowing contact between acid and pigment
This contact causes the Mg atom in the chlorophyll molecules to be displaced & is replaced by 2H atoms
Chlorophyll Pheophytin (Mg free molecules)
Chlorophyll a Pheophytin a ( dull-olive green)
Chlorophyll b Pheophytin b (dull- yellow green)

8. Colour change is irreversible
Chlorophyll a > sensitive than chlorophyll b
Formation of pheophytin depends on;
Presence of H+/ pH – low pH encourages formation
Type of processing- high temp & prolonged time encourage formation
Certain ion present (eg. Fe3+, Zn2+) can replace the colour lost to form stable complex colour

9. Hydrolysis of phytol group
Catalyzed by enzyme chlorophyllase (an esterase) with an optimum activity at 77C
Chlorophyllase catalyses hydrolysis of phytyl ester linkage at C7, forming methyl chlorophyllides
Methyl chlorophyllide can lose its Mg2+ to form pheophorbides, a type of pheophytin, H2O- soluble, dull olive-green colour

10. The effect of acid and heat treatment on chlorophyll
Chlorophyll chlorophyllase chlorophyllide
+acid, heat phytol +acid, heat
- Mg -Mg
Pheophytin Pheophorbide
+heat heat
-CO2CH3 -CO2CH3
Pyropheophytin Pyropheophorbide
*Murano, P.S.,Understanding Food Science & Technology, pg 160