Pigments

FOOD SCIENCE AND PROCESSING 3 (2+1)
Lesson 27 : Processing and Preservation of Fruits - I

Pigments

Like vegetables, fruits also contain different pigments.

  1. Chlorophyll : Guava, gooseberry, country apple.

  2. Carotenoids : Mango, papaya, orange, watermelon (lycopene), musk melon (β- carotene), jackfruit, peaches, (violaxanthin) tomatoes, grape pink (lycopene, b- carotene) pine apple (violaxanthin b- carotene)

  3. Anthocyanins : Grapes, blueberries, plums, cherries.

  4. Anthoxanthins: Guava, apple, gooseberry, pears, custard apple, banana.

  5. Anthocyanins: Sometimes, strawberry jam changes gradually from the pleasing red to a dull reddish brown occurs if such factors as a high pH, oxygen in the head space and or a high storage temperature are present.
    The metal iron precipitates anthocyanin. This reaction may cause ‘pin-holing’ of cans used for foods containing anthocyanins.

  6. Effect of canning or preserving: Whether canned in tin or glass, the colour of the fruits containing anthocyanins deteriorate on storage for extended periods. Deterioration is delayed by storage in a cool dark place.

  7. Effect of sulphur dioxide: Potassium metabisulphite is routinely used as an antimicrobial preservative in squashes and crushes. At high concentrations (1.0 - 1.5 %) it causes a total irreversible bleaching of anthocyanins. Foods containing anthocyanins should not be preserved by potassium metabisulphite. Ex. grape squash or crush.

  8. Water: Fruits contain 75 – 90% water. Dissolved in the water, the bulk of which is found in the vacuoles are soluble substances like sugar, salts, organic acids and water-soluble pigments. Substances unable to dissolve in water are colloidally dispersed in it.

  9. Cellulose and pectic substances: The framework of the fruit is made of cellulose which forms the walls of the plant cells and in which large amounts of water are held.

    Apart from cellulose and hemicelluloses, pectic substances are found in cell walls and between the cells. They act as a cementing substance and bind cells together. Pectic substances include protopectin, the insoluble parent molecule, pectinic acid or pectin and pectic acid. The change in solubility of the pectic substances occurs because of ripening or the influence of heat. This makes tissues disintegrate. Acids make the structure more firm where as alkalies tend to disintegrate the fibres.
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Last modified: Tuesday, 13 December 2011, 8:18 AM